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Application of epimerisation-free amide coupling conditions to the synthesis of matrix metalloprotease inhibitor intermediates
TETRAHEDRON Pergamon
Tetrahedron 54 (1998) 13825-13832
Application of Epimerisation-Free Amide Coupling Conditions to the Synthesis of Matrix Metalloprotease Inhibitor Intermediates.
M. Jonathan Fray* and David Ellis
Departmentof DiscoveryChemistry, PfizerCentralResearch, Sandwich,KentCT13 9NJ, U.K.
Received 3 June 1998; revised 11 August 1998; accepted 3 September 1998
Abstract: Couplingof the N-awl tert-leucinederivative2 with a varietyof amines3a-g gave amides 4a-g in good to excellent yields (75-95%) with minimal epimerisation(_< 3%) at the tert-leucinestereogenic centre. Limitationsof the method are discussed. © 1998 ElsevierScienceLtd. All rights reserved.
INTRODUCTION
Inhibition of matrix metaUoproteases has been postulated as a possible therapeutic approach to a number of disease states, t In connection with a project to investigate the matrix metalloprotease inhibitor potency of a series of succinyl hydroxamates 1, we became interested in the possibility of preparing these compounds more rapidly via amide coupling between the P2' and P3' groups, 2 2 and 3, (Route A, Scheme 1) to give 4. Matrix metalloprotease inhibitors of this structural type are almost always prepared by an alternative method (illustrated for 1 by Route B, Scheme 1), comprising amide coupling of N-tert-butoxycarbonyl (N-Boc) or Nbenzyloxycarbonyl (N-Cbz) protected P2' amino-acid (here tert-leucine) with 3 followed by deprotection to give 5 and subsequent amide coupling with 6 to give 4. Route A would have operational advantages for the synthesis of a large number of derivatives due to the lower total number of reactions involved, but would also be expected to cause difficulties, due to the likelihood of 2 epimerising upon activation by the amide coupling reagent. However, we were prompted to examine Route A in the light of the recent developments in epimerisation-free segment-type amide couplings of peptides reported by Carpino and co-workers. 3 We describe here how Route A may be successfully implemented, without incurring epimerisation, as long as the amine 3 is sufficiently nucleophilic or sterically unhindered.
0040-4020/98/$ - see front matter © 1998 Elsevier Science Ltd. All rights reserved. PII: S0040-4020(98)00836-9
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M. J. Fray. D. Ellis/Tetrahedron 54 (1998) 13825-13832
, PI'
o
f"
H
0
HONH/JL~~ .~N.R OM /~Me e Me 1 P2'
MeOO
P3'
MeO
,
h, Me
O /~'"Me 4
RouteA
Me
Me
~ RouteB
Me
0
~
0
Me-/]L-..o.~J~ H. ' ~ OH + H2N-R M~/le'~O'~~O OH +H2N" 'R~- " H N" 3 Me OMe~MMe Me~MMe 6
5
RESULTS AND DISCUSSION
The enantiomericaUy pure succinic acid mono-ester derivative 64 was coupled to L-tert-leucine benzyl ester 75 (85% yield) followed by hydrogenolysis of the benzyl ester (99% yield) to give the acid 2 (Scheme 2). The amines used in the coupling reactions with 2 are shown in the Figure. We first examined the amide coupling of 2 with a representative amine, (S)-(1-phenyl)ethylamine (3a) under a variety of conditions (see Table, entries 1-3) in an attempt to minimise epimerisation of the tert-leucine chiral centre. As can be seen from the Table (entry 1), coupling using EDC in the presence of hydroxybenzotriazole and Htinig's base led to an almost quantitative yield of product but 4a was contaminated with 29% of the epimer. The amount of epimer was measured from the relative integration of the signals corresponding to the methine hydrogen next to the tert-butyl group at 400 MHz in deuterochloroform solvent. Signals for the major and minor isomers were observed at 8u 4.17 and at 8H 4.26, respectively. The identity of the major isomer was
13827
M. J. Fray. D. Ellis/Tetrahedron 54 (1998) 13825-13832
Scheme 2
Me
O
i
f
"
MeO
O a,b
Me
O
Me
Me
O
¢
H2N-R 3a-i 4a-i
Me
H
Me
_1
0
/ ~ " Me
Me
• ,'~Me
6
C
II 7
Me
2
Reagents and Conditions:
O
(a) N-dimethylaminopropyI-N'-ethylcarbodiimide, 1-hydroxy-1,2,3-benzotriazole,N-melhylmorpholine, 0H2CI2, 0-20°0, 16h. (b) H2 (4 bar), 10% Pd/C, EtOH/H20 = 9:1,20°C, lh. (c) see Table 2.
II H O / ~ " Me Me Me
Figure: Structures of Amines 3a-i
:Me H2N
H2N
H2N'~~
3a
3b
(-)- c/s isomer
(+)- c/s isomer
3f
3g
3e
NH2 3h
Me H2N ' / ~
3d
.© 3e
Me 3i
confu-rned by preparing it using Route B. This result demonstrated the highly sensitive nature of this coupling, which is similar to the coupling between N-benzoylvaline and valine methyl ester (45% epimer formed using the same reagents, DMF solvent). 3g Switching to the coupling agent PyAOP, with coUidine as base led to a significant reduction in epimerisation (entry 2), but, as Carpino has reported, 3c optimal results were obtained by omitting the DMF (entry 3).
13828
M. J. Fray, D. Ellis / Tetrahedron 54 (1998) 13825-13832
Table: Yields and Isomeric Purity of Coupling Products 4a-i
Entry
.. Reaction Conditions
Amine
1
3a
4
EDC, HOBt, i-Pr2NEt, CH2C12, 020°C, 17-24h PyAOP, collidine, CHzC12/DMF (2:1), 0-20°C, 16h PyAOP, collidine, CH2C12, 0-20°C, 16h "
3b
5
"
3c
6
3d
9
PyAOP, collidine, CH2C12, 0°C lh, 20°C 6h. PyAOP, collidine, CH2C12, 0°C lh, 20°C 3h. PyAOP, collidine, CH2CIz, 0-20°C, 16h "
10
"
3h
11
"
3i
2 3
7 8
" "
3e 3f 3g
Product (Yield) 4a (96%) 4a (86%) 4a (86%) 4b (87%) 4c (89%) 4d (87%) 4e (75%) 4f (93%) 4g (95%) 4h (60%)
% Epimer 29% t 8%* < 1% <1% <1% 3% <1% <1% <1% 50%
4i
(0%) Notes to Table. EDC (N-ethyI-N'-dimethyh'uninopropyl-carbodiimide), HOBt (l-hydroxy-l,2,3-benzotriazole),coUidine (2,4,6trimcthylpyridine), PyAOP (7-azabenzotriazol-l-yloxytris(pyrrolidino)phosphonium hexafluorophosphate), DMF (N,N-
dimethylformamide); t Mean of 2 experiments Encouraged by these results, we examined the coupling of 2 with a variety of other amines (entries 4-11). The couplings proceeded in excellent yield and with very little epimerisation, except in three cases, p-Tohiidine (entry 6), having relatively low nucleophilicity, generated slightly more epimer than the alkylamines examined. 9-Aminofluorene (entry 10) afforded a l: 1 mixture of epimers in lower yield.6 Tert-butylamine (entry l 1) gave none of the desired coupling product. Thus, we have shown that the conditions described by Carpino for the segment-type coupling of acylprotected t~-amino acids can be successfully applied to epimerisation-prone couplings of the unnatural aminoacid tert-leucine, with the limitation that the amine partner must be reasonably nucleophilic and unhindered. This methodology may be of use in the parallel synthesis of compound libraries where high diastereomeric purity is preferred to aid interpretation of screening results. One limitation of using PyAOP for amide couplings in
M. J. Fray, D. Ellis / Tetrahedron 54 (I 998) 13825-13832
13829
solution is the necessity to remove the tr/s(pyrrolidino)phosphoramide side product by chromatography, since it is not readily removed by aqueous extraction. The products 4 were converted into the corresponding hydroxamic acids 1 and were screened for inhibitory activity against matrix metalloproteases. The screening results for these compounds will be reported elsewhere.
Acknowledgement. We wish to thank Mr. M. Sproates for his able technical assistance.
EXPERIMENTAL
Melting points were determined using open glass capillary tubes and a Gallenkamp melting point apparatus and are uncorrected. Nuclear magnetic resonance data were obtained using Varian Unity Inova-400 and Varian Unity Inova-300 spectrometers and are quoted in parts per million from tetramethylsilane. Mass spectral data were obtained on a Finnigan Mat. TSQ 7000 or a Fisons Instruments Trio 1000. Infra red spectra were measured using a Nicolet Magna 550 Fourier transform infra-red spectrometer. Combustion analyses were performed by Exeter Analytical (UK) Limited, Uxbridge. Flash chromatography refers to column chromatography on silica gel (Kieselgel 60, 230-400 mesh) from E. Merck, Darmstadt. Kieselgel 60 Fz.~ plates from E. Merck were used for TLC, and compounds were visualised using UV light, 5% aqueous potassium permanganate or Dragendorff's reagent (oversprayed with aqueous sodium nitrite). Hexane refers to a mixture of hexanes (hplc grade) b.p. 65-70°C. Ether refers to diethyl ether. Collidine was dried over potassium hydroxide pellets and distilled. 7-Azabenzotriazol-l-yloxytris(pyrrolidino)phosphonium hexafluorophosphate (PyAOP) was purchased from PerSeptive Biosystems U.K. Ltd. The amines 3a-e and 3h-i were obtained commercially and used without purification. Amines 3f and 3g were prepared according to the literature method, via chromatographic separation of the (S)-O-methylmandelamide derivatives on silica gel] The absolute stereochemistry of 3f ((-) isomer derived from the higher R~ mandelamide) and 3g ((+) isomer derived from the lower Rf mandelamide) has not been assigned, thus the physical data listed for 4f (below) may in fact belong to 4g, and vice versa. tert-Butyl (3R)•3•({[(•S)-••carb•xy•(2•2-dimethy•)pr•py•]amin•}carb•ny•)•6-pheny•-hexan•ate (2). a) N-(Dimethylaminopropyl)-N'-ethylcarbodiimide (88 ! rag, 4.60 mmol) was added to a stirred mixture of tertbutyl (3R)-3-carboxy-6-phenylhexanoic acid (1.22 g, 4.18 mmol), L-tert-leucine benzyl ester hydrochloride (1.077 g, 4.18 mmol), N-methylmorpholine (91 ! gL, 8.36 retool) and 1-hydroxybenzotriazole (704 mg, 4.60 mmol) in dichloromethane (20 mL) under nitrogen at 0°C. After 2 h, the mixture was allowed to warm to room temperature. After 17 h at room temperature, the mixture was poured into ethyl acetate (150 mL) and washed with 5% aqueous citric acid (2 x 75 mL), saturated aqueous sodium bicarbonate (2 x 75 mL), brine (50 mL), dried (MgSO4), and concentrated under reduced pressure. The oily residue was dissolved in cold hexane (20 mL) and the product crystallised as fine colourless needles, which were collected by filtration and dried to give tert-butyl (3R)-3-({ [( IS)-( l-benzyloxycarbonyl)-2,2-dimethylpropyl]amino}carbonyl)-6-phenylhexanoate (1.435 g, 69%), m.p. 86-87 °C. Rf 0.47 (hexane:ethyl acetate= 4:1). The mother liquors were evaporated and recrystallised from hot hexane to afford a further 326 mg (16%) of product. (300 MHz, CDCI3) 0.94 (9H, s), 1.26 (9H, s and IH, m, overlapping), 1.60 (IH, m), 1.69 (2H, m), 2.32 (IH, m,), 2.60 (3H, m), 4.50 (IH, d, J = 9 Hz), 5.09 (1H, d, J = 13 Hz), 5.!4 (1H, d, J = 13 Hz), 6.32 (1H, br d),
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M. J. Fray, D. Ellis / Tetrahedron 54 (1998) 13825-13832
7.15 (3H, m), 7.26 (2H, m), 7.32 (SH, br s). LRMS (APCI) m/z = 496 (MH+), 440 (base peak, MH ÷ - t-Bu). b'TIR v,~. (KBr disc) 3410, 2970, 2940, 1730, 1711, 1680, 1529, 1160, 700 cm ~ Found: C, 72.54; H, 8.35; N, 2.79; C3oH41NO5 requires C, 72.70; H, 8.34; N, 2.83% /
b) A solution of tert-butyl (3R)-3-({[(Is)-(I-benzyloxycarbonyl)-2,2-dimethylpropyl]amino}carbonyl)-6phenylhexanoate (1.60 g, 3.23 mmol) in ethanol:water = 9:1 (55 mL) was hydrogenated over 10% palladium on charcoal (160 mg) at 4 bar and 20°C for lh. The mixture was filtered through Arbocel filter aid and the filter pad was washed with ethanol (50 mL). The filtrate was concentrated under reduced pressure, and the residue passed through a 5 cm plug of silica gel (eluting with ether:hexane:acetic acid = 50:50:1) to remove traces of catalyst. Fractions containing product were concentrated under reduced pressure, redissolved and evaporated sequentially with toluene (3 x 20 mL), ether (2 x 20 mL) and hexane (20 mL) to give (2) as a colourless hygroscopic foam (1.291 g, 99%). Rt 0.61 (hexane:ether:acetic acid = 30:70:1), 8n (400 MHz, CDCI3) 1.01 (9H, s), 1.42 (9H, s and IH, m, overlapping), 1.61 (2H, m), 1.71 (IH, m), 2.33 (1H, m,), 2.61 (4H, m), 4.47 (IH, d, J = 9 Hz), 6.40 (IH, br d, J = 9 Hz), 7.13 (3H, m), 7.26 (2H, m). LRMS (APCI) m/z = 406 (MH+). FTIR v,~,. (KBr disc)2970, 2940, 1729, 1639, 1540, 1370, 1157,700 cm t Found: C, 67.40; H, 8.77; N, 3.43: C23H35NOso0.25HzO requires C, 67.37; H, 8.73; N, 3.42%.
Amide coupling procedure using EDC/HOBt. N-(Dimethylaminopropyl)-N'-ethylcarbodiimidehydrochloride (51.5 mg, 0.269 mmol) was added to a stirred (2) mixture of tert-butyl (3R)-3-({•(IS)-•-carb•xy-(2'2-dim•thy•)pr•py••amin•}carb•ny•)-6-pheny••hexan•ate (99 mg, 0.244 mmol), (S)-(l-phenyl)ethylamine (3a) (32 laL, 0.244 mmol), 1-hydroxy-l,2,3-benzotriazole monohydrate (41 mg, 0.269 mmol) and diisopropylethylamine (42 IlL, 0.244 mmol) in anhydrous dichloromethane (2 mL) under nitrogen at 0°C (ice-water bath). The mixture was allowed to warm to room temperature overnight (17 h) with the cooling bath in place. The mixture was poured into ethyl acetate (50 mL) and washed sequentially with 5% aqueous citric acid (2 x 20 mL), saturated aqueous sodium bicarbonate (2 x 20 mL) and brine (20 mL). The organic solution was dried (MgSO4) and concentrated under reduced pressure to give a mixture of epimeric amides, tert-butyl (3R)-3-({[(1S and 1R))-2,2-dimethyl-l-({[(1S)-lphenylethyl]amino}earbonyl)propyl]amino}carbonyi)-6-(phenyl)hexanoates (121 rag, 98%, isomer ratio 2.75:1), as a colourless foam. Rf 0.26 (hexane:ethyl acetate = 4:1). Spectroscopic and analytical data for pure major isomer (4a): ~ (400 MHz, CDC13) 0.95 (9H, s), 1.39 (3H, d, J = 7 Hz), 1.41 (9H, s and 1H, m, overlapping), 1.65 (3H, m), 2.32 (1H, m,), 2.61 (4H, m), 4.19 (IH, d, J = 9 Hz), 5.06 (1H, pentet, J = 7 Hz), 6.03 (IH, br d, J = 9 Hz), 6.63 (IH, br d, J = 7 Hz), 7.15 (3H, m), 7.29 (7H, m). LRMS (APCI) m/z = 509 (MH+). Found: C, 72.90; H, 8.75; N, 5.51; C31H44N204 requires C, 73.20; H, 8.72; N, 5.50%.
Amide coupling procedure using PyAOP/collidine. 7-Azabenzotriazol-l-yloxytris(pyrrolidino)phosphonium hexafluorophosphate was added in one portion as a
solid to a solution of tert-butyl (3R)-3-({ [(IS)- 1-carboxy-(2,2-dimethyl)propyl]amino}carbonyl)-6-phenylhexanoate (2) (1.0 equiv.), amine (3a-i) (1.0 equiv.) and coUidine (2.0 equiv.) in dry dichloromethane (typically
M. J. Fray, D. Ellis/Tetrahedron 54 (1998) 13825-13832
13831
5-10 ml_Jmmol of 2) under nitrogen at 0°C (ice-water bath). For entry 2 (Table 2) a mixture of anhydrous dimethylformamide and dichloromethane was used. The reactions were stirred for the times indicated in Table 2. 0-20°C, 16h refers to slow warming to room temperature with the ice-water bath in place over a total reaction time of 16 h. The reaction mixture was submitted to the same work-up procedure as described above. Yields in Table 2 refer to isolated yields after column chromatography on silica gel (eluting with hexane/ethyl acetate).
}carb•nyl)pr•pyl]amin•}carb•nyl)tert-Butyl (3R )-3-( {[( •S)-2•2-dimethyl-•-( {[( •S)- •-phenylpr•pyl]amin• 6-(phenyl)hexanoate (4b), colourless foam. Rf 0.7 (toluene:ethyl acetate = 1:1). ~ (400 MHz, CDC13) 0.80 (3H, t, J =7 Hz), 0.92 (9H, s), 1.42 (9H, s), 1.60 (3H, m), 1.73 (3H, m), 2.32 (1H, m), 2.60 (4H, m), 4.20 (1H, d, J = l0 Hz), 5.82 (IH, q, J = 7 Hz), 6.03 (1H, br d, J = 10 Hz), 6.47 (IH, br d, J = 7 Hz), 7.16 (3H, m), 7.29 (7H, m). LRMS (thermospray) m/z = 523 (MH*). Found: C, 73.33; H, 8.86; N, 5.26; C32H46N204requires C, 73.52; H, 8.87; N, 5.36%. tert-Butyl (3R )-3-( {[( •S)-2•2-dimethyl- •-( {[( •R )- •-phenylpr•py•]amin•
}carb•nyl)pr•pyl]amin•
}car••nyl)
-6,(phenyl)hexanoate (4c), colourless foam. Rf 0.64 (toluene:ethyl acetate = 1:1). ~ (400 MHz, CDCI3) 0.90 (3H, t, J = 7 Hz), 1.02 (9H, s), 1.39 (9H, s) 1.48 (4H, m), 1.82 (2H, m), 2.27 (IH, m), 2.52 (4H, m), 4.20 (1H, d, J = 10 Hz), 5.80 (1H, q, J = 7 Hz), 6.03 (IH, br d, J = 10 Hz), 6.37 (IH, br d, J = 7 Hz), 7.06 (3H, m), 7.22 (7H, m). LRMS (thermospray) m/z = 523 (MH+).
tert-Butyl (3R)-3-({ [(1S)-2,2-dimethyl-l-({[4-methylphenyl]amino}carbonyl)propyl]amino}carbonyi) -6-(phenyl)hexanoate (4d), colourless foam. Rf 0.54 (hexane:ethyl acetate = 3:1). ~ (400 MHz, CDC13) 1.06 (9H, s), 1.41 (9H, s and IH, m, overlapping), 1.57 (2H, m), 1.68 (IH, m), 2.31 (3H, s), 2.33 (IH, m), 2.55 (2H, m), 2.63 (2H, m), 4.36 (IH, d, J = l0 Hz), 6.55 (IH, brd, J = 10 Hz), 7.09 (5H, m), 7.16 (2H, m), 7.35 (2H, d, J = 8 Hz), 7.64 (IH, br s). LRMS (thermospray) m/z = 495 (MH~). FFIR v~,~ (KBr disc) 2970, 2930, 1731, 1644, 1539, 1513, 1156, 700 cm a Found: C, 72.80; H, 8.62; N, 5.65; C~oI-h2N~O4requires C, 72.84; H, 8.56; N, 5.66%. tert-Butyl (3R)-3-({[(1S)-2,2-dimethyl- 1-({ 1-pyrrolidinyl}carbonyl)propyl]amino}carbonyl).6-(phenyl)hexanoate (4e), colourless viscous gum. Rf 0.20 (hexane:ethyl acetate = 3: 1). ~l (300 MHz, CDCI3) 1.03 (9H, s), 1.44 (9H, s), 1.58 (3H, m), 1.87 (4H, m), 2.32 (1H, m,), 2.59 (4H, m), 3.39 (2H, m), 3.48 (1H, m), 3.71 (1H, m), 4.67 (1H, d, J = 10 Hz), 6.43 (IH, brd, J = 10 Hz), 7.14 (3H, m), 7.26 (2H, m). LRMS (thermospray) m/z = 459 (MH~. F~'IR v ~ (Nujol mull) 2960, 2930, 2870, 1731, 1635, 1448, 1367, 1158, 700 cm ~ Found: C, 70.45; H, 9.31; N, 6.08; C27H42NzO4requires C, 70.71; H, 9.23; N, 6.11%. tert-Butyl (3R)-3-({[(1S)-2,2-dimethyl-l-({[(1S, 2S)-2-phenylcyclopropyl]amino}carbonyl)propyl]amino}carbonyl)-6-(phenyl)hexanoate (4f), colourless foam. Rr 0.6 (toluene:ethyl acetate = 1:1). ~ (400 MHz, CDCI3) 0.69 (9H, s), 1.00 (1H, m), 1,29 (1H, m), 1.40 (9H, s and IH, m, overlapping), 1.60 (3H, m), 2.31 (2H, m), 2.58 (4H, m), 3.15 (1H, m), 3.90 (1H, d, J = 10 Hz), 5.33 (1H, br s), 6.39 (1H, br d, J = 10 Hz), 7.22 (10H, m). LRMS (APCI) m/z = 521 (MH+). Found: C, 73.65; H, 8.61; N, 5.38; C32H44N204 requires C, 73.81; H, 8.52; N, 5.38%. tert-Butyl (3R)-3-({[(1S)-2,2-dimethyl-l.({[(1R, 2R)-2-phenylcyclopropyl]amino}carbonyl)propyl]amino}carbonyl)-6-(phenyl)hexanoate (4g), colourless solid, m.p. 161-163.5°C. Rf 0.6 (toluene:ethyl acetate = 1:1).
13832
M. J. Fray, D. Ellis/Tetrahedron 54 (I 998) 13825-13832
(300 MHz, CDC13) 0.80 (9H, s), 1.00 (IH, m), 1.40 (9H, s and 1H, m, overlapping), 1.59 (4H, m), 2.29 (2H, m), 2.55 (4H, m), 2.98 (1H, m), 3.87 (IH, d, J = I0 Hz), 5.16 (IH, br s), 6.29 (1H, br d, J = 10 Hz), 7.20 (10H, m). LRMS (thermospray) ndz =,' 521 (MI-V). Found: C, 73.86; H, 8.55; N, 5.38; C32I"~N204 requires C, 73.81; H, 8.52; N, 5.38%.
tert-Butyl (3R)-3-({[(1R and lS)-2,2-dimethyl-l-({[9-fluorenyl]amino}carbonyl)propyl]amino}carbonyl)6-(phenyl)hexanoate (4h), colourless foam. Rf 0.73 (toluene:ethyl acetate = 1:1). ~ (400 MHz, DMSO-~) 0.97 (9H, s), 1.34 (9H, s and 1H, m, overlapping), 1.55 (3H, m), 2.20 (IH, dd, J = 5 and 15 Hz), 2.42 (1H, m), 2.56 (2H, m), 2.87 (IH, m), 4.33 (1H, d, J = 10 Hz), 6.03 (IH, d), 7.15 (4H, m), 7.27 (4H, m), 7.40 (3H, m), 7.84 (2H, d, J = 8 Hz and 1H, br d, overlapping), 8.53 (2 x 0.5H overlapping, each d, J = 8 Hz). LRMS (thermospray) m/z = 569 (MH'). Found: C, 75.93; H, 7.90; N, 4.80; C36I-t44N:O4 requires C, 76.02; H, 7.80; N, 4.93%.
REFERENCES 1. (a) Beckett, R.P.; Whittaker, M.; Expert Opin. Ther. Pat., 1998, 8, 259-82. (b) Denis, L.J.; Verweij, J.; Invest New Drugs, 1997, 15, 175-185. (c) Wojtowicz-Praga, S.M.; Dickson, R.B.; Hawkins, M.J.; Invest New Drugs, 1997, 15, 61-75. (d) Davidson, A.; Drummond, A.H.; Galloway, W.A.; Whittaker, M.; Che~ Ind. (London), 1997, 258-261. (e) Beckett, R.P.; Expert Opin. Ther. Pat., 1996, 6, 1305-15. (1) Hagmann, W.K.; Larkk, M.W.; Becker, J.W.;Annu. Rep. Med. Chem., 1996, 31,231-40. (g) Beckett, R.P.; Davidson, A.; Drummond, A.H.; Huxley, P.; Whittaker, M.; Drug Discovery Today, 1996, 1, 16-26. (h) Zask, A.; Levin, J.I.; Killar, L.M.; Skotnicki, LS.; Curr. Pharra. Design, 1996, 2, 624. 2. Berger, A.; Schechter, I.; Phil. Trans. R. Soc. London B, 1970, 257, 249-64. 3. (a) Albercio, F.; Cases, M.; Alsina, J.; Triolo, S.A.; Carpino, L.A.; Kates, S.A.; Tetrahedron Lett., 1997, 38, 4853-6. (b) Ehrlich, A.; Heyne, H-U.; Winter, R.; Beyermann, M.; Haber, H.; Carpino, L.A.; Bienert, M.; J. Org. ChertL, 1996, 61, 8831-8. (c) Carpino, L.A.; lonescu, D.; EI-Faham, A.; J. Org. Chem., 1996, 61, 2460-5. (d) Carpino, L.A.; El-Faham, A.; Albcrcio, F.; J. Org. Chem., 1995, 60, 3561-4. (e) Carpino, L.A.; E1-Faham, A.; Albercio, F.; Tetrahedron Lett., 1994, 35, 2279-82. (f) Carpino, L.A.; EI-Faham, A.; Minor, C.A.; Albercio, F.; J. Chem. Soc. Chem. Commun., 1994, 210-3. (g) Carpino, L.A.; J. Am. Chem. Soc., 1993, 115, 4397-8. For two recent reviews on peptide coupling reactions see: Albercio, F.; Carpino, L.A.; Methods Enzymol., 1997, 289 (Solid-Phase Peptide Synthesis), 104-126 and Lloyd-Williams, P.; Albercio, F.; Giralt, E.; Tetrahedron, 1993, 48, 11065. 4. Porter, J.R.; Beeley, N.R.A.; Boyce, B.; Mason, B.; Millican, A.; Millar, K.; Leonard, J.; Morphy, J.R.; O'Connell, J.P.; Bioorg. Med. Chem. Lett., 1994, 4, 2741-6. 5. Moss, N.; Beaulieu, P.; Duceppe, J-S.; Ferland, J-M.; Gauthier, J.; Ghiro, E.; Goulet, S.; Guse, I.; LlinasBrunet, M.; et al., J. Med. Chera., 1996, 39, 2178-87. 6. In the case of 4h the diastereomeric ratio was measured using the fluorenylamide NH signal (DMSO-~ solvent). 7. Lind, P.T.; Morin, J.M.; Noreen, R.; Ternansky, R.J.; World Patent Application WO 9303022.
Tetrahedron 54 (1998) 13825-13832
Application of Epimerisation-Free Amide Coupling Conditions to the Synthesis of Matrix Metalloprotease Inhibitor Intermediates.
M. Jonathan Fray* and David Ellis
Departmentof DiscoveryChemistry, PfizerCentralResearch, Sandwich,KentCT13 9NJ, U.K.
Received 3 June 1998; revised 11 August 1998; accepted 3 September 1998
Abstract: Couplingof the N-awl tert-leucinederivative2 with a varietyof amines3a-g gave amides 4a-g in good to excellent yields (75-95%) with minimal epimerisation(_< 3%) at the tert-leucinestereogenic centre. Limitationsof the method are discussed. © 1998 ElsevierScienceLtd. All rights reserved.
INTRODUCTION
Inhibition of matrix metaUoproteases has been postulated as a possible therapeutic approach to a number of disease states, t In connection with a project to investigate the matrix metalloprotease inhibitor potency of a series of succinyl hydroxamates 1, we became interested in the possibility of preparing these compounds more rapidly via amide coupling between the P2' and P3' groups, 2 2 and 3, (Route A, Scheme 1) to give 4. Matrix metalloprotease inhibitors of this structural type are almost always prepared by an alternative method (illustrated for 1 by Route B, Scheme 1), comprising amide coupling of N-tert-butoxycarbonyl (N-Boc) or Nbenzyloxycarbonyl (N-Cbz) protected P2' amino-acid (here tert-leucine) with 3 followed by deprotection to give 5 and subsequent amide coupling with 6 to give 4. Route A would have operational advantages for the synthesis of a large number of derivatives due to the lower total number of reactions involved, but would also be expected to cause difficulties, due to the likelihood of 2 epimerising upon activation by the amide coupling reagent. However, we were prompted to examine Route A in the light of the recent developments in epimerisation-free segment-type amide couplings of peptides reported by Carpino and co-workers. 3 We describe here how Route A may be successfully implemented, without incurring epimerisation, as long as the amine 3 is sufficiently nucleophilic or sterically unhindered.
0040-4020/98/$ - see front matter © 1998 Elsevier Science Ltd. All rights reserved. PII: S0040-4020(98)00836-9
13826
M. J. Fray. D. Ellis/Tetrahedron 54 (1998) 13825-13832
, PI'
o
f"
H
0
HONH/JL~~ .~N.R OM /~Me e Me 1 P2'
MeOO
P3'
MeO
,
h, Me
O /~'"Me 4
RouteA
Me
Me
~ RouteB
Me
0
~
0
Me-/]L-..o.~J~ H. ' ~ OH + H2N-R M~/le'~O'~~O OH +H2N" 'R~- " H N" 3 Me OMe~MMe Me~MMe 6
5
RESULTS AND DISCUSSION
The enantiomericaUy pure succinic acid mono-ester derivative 64 was coupled to L-tert-leucine benzyl ester 75 (85% yield) followed by hydrogenolysis of the benzyl ester (99% yield) to give the acid 2 (Scheme 2). The amines used in the coupling reactions with 2 are shown in the Figure. We first examined the amide coupling of 2 with a representative amine, (S)-(1-phenyl)ethylamine (3a) under a variety of conditions (see Table, entries 1-3) in an attempt to minimise epimerisation of the tert-leucine chiral centre. As can be seen from the Table (entry 1), coupling using EDC in the presence of hydroxybenzotriazole and Htinig's base led to an almost quantitative yield of product but 4a was contaminated with 29% of the epimer. The amount of epimer was measured from the relative integration of the signals corresponding to the methine hydrogen next to the tert-butyl group at 400 MHz in deuterochloroform solvent. Signals for the major and minor isomers were observed at 8u 4.17 and at 8H 4.26, respectively. The identity of the major isomer was
13827
M. J. Fray. D. Ellis/Tetrahedron 54 (1998) 13825-13832
Scheme 2
Me
O
i
f
"
MeO
O a,b
Me
O
Me
Me
O
¢
H2N-R 3a-i 4a-i
Me
H
Me
_1
0
/ ~ " Me
Me
• ,'~Me
6
C
II 7
Me
2
Reagents and Conditions:
O
(a) N-dimethylaminopropyI-N'-ethylcarbodiimide, 1-hydroxy-1,2,3-benzotriazole,N-melhylmorpholine, 0H2CI2, 0-20°0, 16h. (b) H2 (4 bar), 10% Pd/C, EtOH/H20 = 9:1,20°C, lh. (c) see Table 2.
II H O / ~ " Me Me Me
Figure: Structures of Amines 3a-i
:Me H2N
H2N
H2N'~~
3a
3b
(-)- c/s isomer
(+)- c/s isomer
3f
3g
3e
NH2 3h
Me H2N ' / ~
3d
.© 3e
Me 3i
confu-rned by preparing it using Route B. This result demonstrated the highly sensitive nature of this coupling, which is similar to the coupling between N-benzoylvaline and valine methyl ester (45% epimer formed using the same reagents, DMF solvent). 3g Switching to the coupling agent PyAOP, with coUidine as base led to a significant reduction in epimerisation (entry 2), but, as Carpino has reported, 3c optimal results were obtained by omitting the DMF (entry 3).
13828
M. J. Fray, D. Ellis / Tetrahedron 54 (1998) 13825-13832
Table: Yields and Isomeric Purity of Coupling Products 4a-i
Entry
.. Reaction Conditions
Amine
1
3a
4
EDC, HOBt, i-Pr2NEt, CH2C12, 020°C, 17-24h PyAOP, collidine, CHzC12/DMF (2:1), 0-20°C, 16h PyAOP, collidine, CH2C12, 0-20°C, 16h "
3b
5
"
3c
6
3d
9
PyAOP, collidine, CH2C12, 0°C lh, 20°C 6h. PyAOP, collidine, CH2C12, 0°C lh, 20°C 3h. PyAOP, collidine, CH2CIz, 0-20°C, 16h "
10
"
3h
11
"
3i
2 3
7 8
" "
3e 3f 3g
Product (Yield) 4a (96%) 4a (86%) 4a (86%) 4b (87%) 4c (89%) 4d (87%) 4e (75%) 4f (93%) 4g (95%) 4h (60%)
% Epimer 29% t 8%* < 1% <1% <1% 3% <1% <1% <1% 50%
4i
(0%) Notes to Table. EDC (N-ethyI-N'-dimethyh'uninopropyl-carbodiimide), HOBt (l-hydroxy-l,2,3-benzotriazole),coUidine (2,4,6trimcthylpyridine), PyAOP (7-azabenzotriazol-l-yloxytris(pyrrolidino)phosphonium hexafluorophosphate), DMF (N,N-
dimethylformamide); t Mean of 2 experiments Encouraged by these results, we examined the coupling of 2 with a variety of other amines (entries 4-11). The couplings proceeded in excellent yield and with very little epimerisation, except in three cases, p-Tohiidine (entry 6), having relatively low nucleophilicity, generated slightly more epimer than the alkylamines examined. 9-Aminofluorene (entry 10) afforded a l: 1 mixture of epimers in lower yield.6 Tert-butylamine (entry l 1) gave none of the desired coupling product. Thus, we have shown that the conditions described by Carpino for the segment-type coupling of acylprotected t~-amino acids can be successfully applied to epimerisation-prone couplings of the unnatural aminoacid tert-leucine, with the limitation that the amine partner must be reasonably nucleophilic and unhindered. This methodology may be of use in the parallel synthesis of compound libraries where high diastereomeric purity is preferred to aid interpretation of screening results. One limitation of using PyAOP for amide couplings in
M. J. Fray, D. Ellis / Tetrahedron 54 (I 998) 13825-13832
13829
solution is the necessity to remove the tr/s(pyrrolidino)phosphoramide side product by chromatography, since it is not readily removed by aqueous extraction. The products 4 were converted into the corresponding hydroxamic acids 1 and were screened for inhibitory activity against matrix metalloproteases. The screening results for these compounds will be reported elsewhere.
Acknowledgement. We wish to thank Mr. M. Sproates for his able technical assistance.
EXPERIMENTAL
Melting points were determined using open glass capillary tubes and a Gallenkamp melting point apparatus and are uncorrected. Nuclear magnetic resonance data were obtained using Varian Unity Inova-400 and Varian Unity Inova-300 spectrometers and are quoted in parts per million from tetramethylsilane. Mass spectral data were obtained on a Finnigan Mat. TSQ 7000 or a Fisons Instruments Trio 1000. Infra red spectra were measured using a Nicolet Magna 550 Fourier transform infra-red spectrometer. Combustion analyses were performed by Exeter Analytical (UK) Limited, Uxbridge. Flash chromatography refers to column chromatography on silica gel (Kieselgel 60, 230-400 mesh) from E. Merck, Darmstadt. Kieselgel 60 Fz.~ plates from E. Merck were used for TLC, and compounds were visualised using UV light, 5% aqueous potassium permanganate or Dragendorff's reagent (oversprayed with aqueous sodium nitrite). Hexane refers to a mixture of hexanes (hplc grade) b.p. 65-70°C. Ether refers to diethyl ether. Collidine was dried over potassium hydroxide pellets and distilled. 7-Azabenzotriazol-l-yloxytris(pyrrolidino)phosphonium hexafluorophosphate (PyAOP) was purchased from PerSeptive Biosystems U.K. Ltd. The amines 3a-e and 3h-i were obtained commercially and used without purification. Amines 3f and 3g were prepared according to the literature method, via chromatographic separation of the (S)-O-methylmandelamide derivatives on silica gel] The absolute stereochemistry of 3f ((-) isomer derived from the higher R~ mandelamide) and 3g ((+) isomer derived from the lower Rf mandelamide) has not been assigned, thus the physical data listed for 4f (below) may in fact belong to 4g, and vice versa. tert-Butyl (3R)•3•({[(•S)-••carb•xy•(2•2-dimethy•)pr•py•]amin•}carb•ny•)•6-pheny•-hexan•ate (2). a) N-(Dimethylaminopropyl)-N'-ethylcarbodiimide (88 ! rag, 4.60 mmol) was added to a stirred mixture of tertbutyl (3R)-3-carboxy-6-phenylhexanoic acid (1.22 g, 4.18 mmol), L-tert-leucine benzyl ester hydrochloride (1.077 g, 4.18 mmol), N-methylmorpholine (91 ! gL, 8.36 retool) and 1-hydroxybenzotriazole (704 mg, 4.60 mmol) in dichloromethane (20 mL) under nitrogen at 0°C. After 2 h, the mixture was allowed to warm to room temperature. After 17 h at room temperature, the mixture was poured into ethyl acetate (150 mL) and washed with 5% aqueous citric acid (2 x 75 mL), saturated aqueous sodium bicarbonate (2 x 75 mL), brine (50 mL), dried (MgSO4), and concentrated under reduced pressure. The oily residue was dissolved in cold hexane (20 mL) and the product crystallised as fine colourless needles, which were collected by filtration and dried to give tert-butyl (3R)-3-({ [( IS)-( l-benzyloxycarbonyl)-2,2-dimethylpropyl]amino}carbonyl)-6-phenylhexanoate (1.435 g, 69%), m.p. 86-87 °C. Rf 0.47 (hexane:ethyl acetate= 4:1). The mother liquors were evaporated and recrystallised from hot hexane to afford a further 326 mg (16%) of product. (300 MHz, CDCI3) 0.94 (9H, s), 1.26 (9H, s and IH, m, overlapping), 1.60 (IH, m), 1.69 (2H, m), 2.32 (IH, m,), 2.60 (3H, m), 4.50 (IH, d, J = 9 Hz), 5.09 (1H, d, J = 13 Hz), 5.!4 (1H, d, J = 13 Hz), 6.32 (1H, br d),
13830
M. J. Fray, D. Ellis / Tetrahedron 54 (1998) 13825-13832
7.15 (3H, m), 7.26 (2H, m), 7.32 (SH, br s). LRMS (APCI) m/z = 496 (MH+), 440 (base peak, MH ÷ - t-Bu). b'TIR v,~. (KBr disc) 3410, 2970, 2940, 1730, 1711, 1680, 1529, 1160, 700 cm ~ Found: C, 72.54; H, 8.35; N, 2.79; C3oH41NO5 requires C, 72.70; H, 8.34; N, 2.83% /
b) A solution of tert-butyl (3R)-3-({[(Is)-(I-benzyloxycarbonyl)-2,2-dimethylpropyl]amino}carbonyl)-6phenylhexanoate (1.60 g, 3.23 mmol) in ethanol:water = 9:1 (55 mL) was hydrogenated over 10% palladium on charcoal (160 mg) at 4 bar and 20°C for lh. The mixture was filtered through Arbocel filter aid and the filter pad was washed with ethanol (50 mL). The filtrate was concentrated under reduced pressure, and the residue passed through a 5 cm plug of silica gel (eluting with ether:hexane:acetic acid = 50:50:1) to remove traces of catalyst. Fractions containing product were concentrated under reduced pressure, redissolved and evaporated sequentially with toluene (3 x 20 mL), ether (2 x 20 mL) and hexane (20 mL) to give (2) as a colourless hygroscopic foam (1.291 g, 99%). Rt 0.61 (hexane:ether:acetic acid = 30:70:1), 8n (400 MHz, CDCI3) 1.01 (9H, s), 1.42 (9H, s and IH, m, overlapping), 1.61 (2H, m), 1.71 (IH, m), 2.33 (1H, m,), 2.61 (4H, m), 4.47 (IH, d, J = 9 Hz), 6.40 (IH, br d, J = 9 Hz), 7.13 (3H, m), 7.26 (2H, m). LRMS (APCI) m/z = 406 (MH+). FTIR v,~,. (KBr disc)2970, 2940, 1729, 1639, 1540, 1370, 1157,700 cm t Found: C, 67.40; H, 8.77; N, 3.43: C23H35NOso0.25HzO requires C, 67.37; H, 8.73; N, 3.42%.
Amide coupling procedure using EDC/HOBt. N-(Dimethylaminopropyl)-N'-ethylcarbodiimidehydrochloride (51.5 mg, 0.269 mmol) was added to a stirred (2) mixture of tert-butyl (3R)-3-({•(IS)-•-carb•xy-(2'2-dim•thy•)pr•py••amin•}carb•ny•)-6-pheny••hexan•ate (99 mg, 0.244 mmol), (S)-(l-phenyl)ethylamine (3a) (32 laL, 0.244 mmol), 1-hydroxy-l,2,3-benzotriazole monohydrate (41 mg, 0.269 mmol) and diisopropylethylamine (42 IlL, 0.244 mmol) in anhydrous dichloromethane (2 mL) under nitrogen at 0°C (ice-water bath). The mixture was allowed to warm to room temperature overnight (17 h) with the cooling bath in place. The mixture was poured into ethyl acetate (50 mL) and washed sequentially with 5% aqueous citric acid (2 x 20 mL), saturated aqueous sodium bicarbonate (2 x 20 mL) and brine (20 mL). The organic solution was dried (MgSO4) and concentrated under reduced pressure to give a mixture of epimeric amides, tert-butyl (3R)-3-({[(1S and 1R))-2,2-dimethyl-l-({[(1S)-lphenylethyl]amino}earbonyl)propyl]amino}carbonyi)-6-(phenyl)hexanoates (121 rag, 98%, isomer ratio 2.75:1), as a colourless foam. Rf 0.26 (hexane:ethyl acetate = 4:1). Spectroscopic and analytical data for pure major isomer (4a): ~ (400 MHz, CDC13) 0.95 (9H, s), 1.39 (3H, d, J = 7 Hz), 1.41 (9H, s and 1H, m, overlapping), 1.65 (3H, m), 2.32 (1H, m,), 2.61 (4H, m), 4.19 (IH, d, J = 9 Hz), 5.06 (1H, pentet, J = 7 Hz), 6.03 (IH, br d, J = 9 Hz), 6.63 (IH, br d, J = 7 Hz), 7.15 (3H, m), 7.29 (7H, m). LRMS (APCI) m/z = 509 (MH+). Found: C, 72.90; H, 8.75; N, 5.51; C31H44N204 requires C, 73.20; H, 8.72; N, 5.50%.
Amide coupling procedure using PyAOP/collidine. 7-Azabenzotriazol-l-yloxytris(pyrrolidino)phosphonium hexafluorophosphate was added in one portion as a
solid to a solution of tert-butyl (3R)-3-({ [(IS)- 1-carboxy-(2,2-dimethyl)propyl]amino}carbonyl)-6-phenylhexanoate (2) (1.0 equiv.), amine (3a-i) (1.0 equiv.) and coUidine (2.0 equiv.) in dry dichloromethane (typically
M. J. Fray, D. Ellis/Tetrahedron 54 (1998) 13825-13832
13831
5-10 ml_Jmmol of 2) under nitrogen at 0°C (ice-water bath). For entry 2 (Table 2) a mixture of anhydrous dimethylformamide and dichloromethane was used. The reactions were stirred for the times indicated in Table 2. 0-20°C, 16h refers to slow warming to room temperature with the ice-water bath in place over a total reaction time of 16 h. The reaction mixture was submitted to the same work-up procedure as described above. Yields in Table 2 refer to isolated yields after column chromatography on silica gel (eluting with hexane/ethyl acetate).
}carb•nyl)pr•pyl]amin•}carb•nyl)tert-Butyl (3R )-3-( {[( •S)-2•2-dimethyl-•-( {[( •S)- •-phenylpr•pyl]amin• 6-(phenyl)hexanoate (4b), colourless foam. Rf 0.7 (toluene:ethyl acetate = 1:1). ~ (400 MHz, CDC13) 0.80 (3H, t, J =7 Hz), 0.92 (9H, s), 1.42 (9H, s), 1.60 (3H, m), 1.73 (3H, m), 2.32 (1H, m), 2.60 (4H, m), 4.20 (1H, d, J = l0 Hz), 5.82 (IH, q, J = 7 Hz), 6.03 (1H, br d, J = 10 Hz), 6.47 (IH, br d, J = 7 Hz), 7.16 (3H, m), 7.29 (7H, m). LRMS (thermospray) m/z = 523 (MH*). Found: C, 73.33; H, 8.86; N, 5.26; C32H46N204requires C, 73.52; H, 8.87; N, 5.36%. tert-Butyl (3R )-3-( {[( •S)-2•2-dimethyl- •-( {[( •R )- •-phenylpr•py•]amin•
}carb•nyl)pr•pyl]amin•
}car••nyl)
-6,(phenyl)hexanoate (4c), colourless foam. Rf 0.64 (toluene:ethyl acetate = 1:1). ~ (400 MHz, CDCI3) 0.90 (3H, t, J = 7 Hz), 1.02 (9H, s), 1.39 (9H, s) 1.48 (4H, m), 1.82 (2H, m), 2.27 (IH, m), 2.52 (4H, m), 4.20 (1H, d, J = 10 Hz), 5.80 (1H, q, J = 7 Hz), 6.03 (IH, br d, J = 10 Hz), 6.37 (IH, br d, J = 7 Hz), 7.06 (3H, m), 7.22 (7H, m). LRMS (thermospray) m/z = 523 (MH+).
tert-Butyl (3R)-3-({ [(1S)-2,2-dimethyl-l-({[4-methylphenyl]amino}carbonyl)propyl]amino}carbonyi) -6-(phenyl)hexanoate (4d), colourless foam. Rf 0.54 (hexane:ethyl acetate = 3:1). ~ (400 MHz, CDC13) 1.06 (9H, s), 1.41 (9H, s and IH, m, overlapping), 1.57 (2H, m), 1.68 (IH, m), 2.31 (3H, s), 2.33 (IH, m), 2.55 (2H, m), 2.63 (2H, m), 4.36 (IH, d, J = l0 Hz), 6.55 (IH, brd, J = 10 Hz), 7.09 (5H, m), 7.16 (2H, m), 7.35 (2H, d, J = 8 Hz), 7.64 (IH, br s). LRMS (thermospray) m/z = 495 (MH~). FFIR v~,~ (KBr disc) 2970, 2930, 1731, 1644, 1539, 1513, 1156, 700 cm a Found: C, 72.80; H, 8.62; N, 5.65; C~oI-h2N~O4requires C, 72.84; H, 8.56; N, 5.66%. tert-Butyl (3R)-3-({[(1S)-2,2-dimethyl- 1-({ 1-pyrrolidinyl}carbonyl)propyl]amino}carbonyl).6-(phenyl)hexanoate (4e), colourless viscous gum. Rf 0.20 (hexane:ethyl acetate = 3: 1). ~l (300 MHz, CDCI3) 1.03 (9H, s), 1.44 (9H, s), 1.58 (3H, m), 1.87 (4H, m), 2.32 (1H, m,), 2.59 (4H, m), 3.39 (2H, m), 3.48 (1H, m), 3.71 (1H, m), 4.67 (1H, d, J = 10 Hz), 6.43 (IH, brd, J = 10 Hz), 7.14 (3H, m), 7.26 (2H, m). LRMS (thermospray) m/z = 459 (MH~. F~'IR v ~ (Nujol mull) 2960, 2930, 2870, 1731, 1635, 1448, 1367, 1158, 700 cm ~ Found: C, 70.45; H, 9.31; N, 6.08; C27H42NzO4requires C, 70.71; H, 9.23; N, 6.11%. tert-Butyl (3R)-3-({[(1S)-2,2-dimethyl-l-({[(1S, 2S)-2-phenylcyclopropyl]amino}carbonyl)propyl]amino}carbonyl)-6-(phenyl)hexanoate (4f), colourless foam. Rr 0.6 (toluene:ethyl acetate = 1:1). ~ (400 MHz, CDCI3) 0.69 (9H, s), 1.00 (1H, m), 1,29 (1H, m), 1.40 (9H, s and IH, m, overlapping), 1.60 (3H, m), 2.31 (2H, m), 2.58 (4H, m), 3.15 (1H, m), 3.90 (1H, d, J = 10 Hz), 5.33 (1H, br s), 6.39 (1H, br d, J = 10 Hz), 7.22 (10H, m). LRMS (APCI) m/z = 521 (MH+). Found: C, 73.65; H, 8.61; N, 5.38; C32H44N204 requires C, 73.81; H, 8.52; N, 5.38%. tert-Butyl (3R)-3-({[(1S)-2,2-dimethyl-l.({[(1R, 2R)-2-phenylcyclopropyl]amino}carbonyl)propyl]amino}carbonyl)-6-(phenyl)hexanoate (4g), colourless solid, m.p. 161-163.5°C. Rf 0.6 (toluene:ethyl acetate = 1:1).
13832
M. J. Fray, D. Ellis/Tetrahedron 54 (I 998) 13825-13832
(300 MHz, CDC13) 0.80 (9H, s), 1.00 (IH, m), 1.40 (9H, s and 1H, m, overlapping), 1.59 (4H, m), 2.29 (2H, m), 2.55 (4H, m), 2.98 (1H, m), 3.87 (IH, d, J = I0 Hz), 5.16 (IH, br s), 6.29 (1H, br d, J = 10 Hz), 7.20 (10H, m). LRMS (thermospray) ndz =,' 521 (MI-V). Found: C, 73.86; H, 8.55; N, 5.38; C32I"~N204 requires C, 73.81; H, 8.52; N, 5.38%.
tert-Butyl (3R)-3-({[(1R and lS)-2,2-dimethyl-l-({[9-fluorenyl]amino}carbonyl)propyl]amino}carbonyl)6-(phenyl)hexanoate (4h), colourless foam. Rf 0.73 (toluene:ethyl acetate = 1:1). ~ (400 MHz, DMSO-~) 0.97 (9H, s), 1.34 (9H, s and 1H, m, overlapping), 1.55 (3H, m), 2.20 (IH, dd, J = 5 and 15 Hz), 2.42 (1H, m), 2.56 (2H, m), 2.87 (IH, m), 4.33 (1H, d, J = 10 Hz), 6.03 (IH, d), 7.15 (4H, m), 7.27 (4H, m), 7.40 (3H, m), 7.84 (2H, d, J = 8 Hz and 1H, br d, overlapping), 8.53 (2 x 0.5H overlapping, each d, J = 8 Hz). LRMS (thermospray) m/z = 569 (MH'). Found: C, 75.93; H, 7.90; N, 4.80; C36I-t44N:O4 requires C, 76.02; H, 7.80; N, 4.93%.
REFERENCES 1. (a) Beckett, R.P.; Whittaker, M.; Expert Opin. Ther. Pat., 1998, 8, 259-82. (b) Denis, L.J.; Verweij, J.; Invest New Drugs, 1997, 15, 175-185. (c) Wojtowicz-Praga, S.M.; Dickson, R.B.; Hawkins, M.J.; Invest New Drugs, 1997, 15, 61-75. (d) Davidson, A.; Drummond, A.H.; Galloway, W.A.; Whittaker, M.; Che~ Ind. (London), 1997, 258-261. (e) Beckett, R.P.; Expert Opin. Ther. Pat., 1996, 6, 1305-15. (1) Hagmann, W.K.; Larkk, M.W.; Becker, J.W.;Annu. Rep. Med. Chem., 1996, 31,231-40. (g) Beckett, R.P.; Davidson, A.; Drummond, A.H.; Huxley, P.; Whittaker, M.; Drug Discovery Today, 1996, 1, 16-26. (h) Zask, A.; Levin, J.I.; Killar, L.M.; Skotnicki, LS.; Curr. Pharra. Design, 1996, 2, 624. 2. Berger, A.; Schechter, I.; Phil. Trans. R. Soc. London B, 1970, 257, 249-64. 3. (a) Albercio, F.; Cases, M.; Alsina, J.; Triolo, S.A.; Carpino, L.A.; Kates, S.A.; Tetrahedron Lett., 1997, 38, 4853-6. (b) Ehrlich, A.; Heyne, H-U.; Winter, R.; Beyermann, M.; Haber, H.; Carpino, L.A.; Bienert, M.; J. Org. ChertL, 1996, 61, 8831-8. (c) Carpino, L.A.; lonescu, D.; EI-Faham, A.; J. Org. Chem., 1996, 61, 2460-5. (d) Carpino, L.A.; El-Faham, A.; Albcrcio, F.; J. Org. Chem., 1995, 60, 3561-4. (e) Carpino, L.A.; E1-Faham, A.; Albercio, F.; Tetrahedron Lett., 1994, 35, 2279-82. (f) Carpino, L.A.; EI-Faham, A.; Minor, C.A.; Albercio, F.; J. Chem. Soc. Chem. Commun., 1994, 210-3. (g) Carpino, L.A.; J. Am. Chem. Soc., 1993, 115, 4397-8. For two recent reviews on peptide coupling reactions see: Albercio, F.; Carpino, L.A.; Methods Enzymol., 1997, 289 (Solid-Phase Peptide Synthesis), 104-126 and Lloyd-Williams, P.; Albercio, F.; Giralt, E.; Tetrahedron, 1993, 48, 11065. 4. Porter, J.R.; Beeley, N.R.A.; Boyce, B.; Mason, B.; Millican, A.; Millar, K.; Leonard, J.; Morphy, J.R.; O'Connell, J.P.; Bioorg. Med. Chem. Lett., 1994, 4, 2741-6. 5. Moss, N.; Beaulieu, P.; Duceppe, J-S.; Ferland, J-M.; Gauthier, J.; Ghiro, E.; Goulet, S.; Guse, I.; LlinasBrunet, M.; et al., J. Med. Chera., 1996, 39, 2178-87. 6. In the case of 4h the diastereomeric ratio was measured using the fluorenylamide NH signal (DMSO-~ solvent). 7. Lind, P.T.; Morin, J.M.; Noreen, R.; Ternansky, R.J.; World Patent Application WO 9303022.