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Enzymatic preparation of optically active 7-oxabicyclo[2.2.1] heptane derivatives
oo4o-4o20/88 s3.oo+m Pcrgamon hlm& Ltd.
mmkdrm~ vol. 44. No. 2, pp. 389 to 39Z1988 Printed in Great Britain.
WZYMATIC PREPARATION OF OPTICALLY ACTIVZ 'I-OZARICYCLO[ 2.2.13RZPTANZ DERIVATIVES
R.Saf, K.Faber,
G.Penn and H.Griengl*
Institute of Organic Chemistry, Technical Dnfverzity Graz, Stremayrgazse 16, A-0010 Gxaz, Austria (Receiaed in Germany 2 1September 1987)
endo-7-oxabicyclo - Enzymatic resolution of hept-2-yl'butyratea 3 aud 5 wing lipaze from bicyclic Candfde cylfndracea led to optically alcohols and e&era being impcwtant inteskm for the eynthesi~~of biologically active compounda.
INTRODUCTION 7-Oxabicyclol2.2.11heptane derivatives have gained increasing importance as starting material for the preparation of "naked sugars"1,2 themselves being valuable intermediates for the syntheeiz of biologically active compounds such 2,4 and C-nucleoeides5 . Their versatility as as nonactic acid3, dsiinozamine synthetic tools has recently been demonstrated by regio- and stereospecific functionalisation of 'I-oxabicyclol2.2.11hept-5-en-a-one (1)6 Qwolving carbon atoms C-27, C-33 and C-S/C-6*. Although practical and efficient syntheses for racemic ketone 1 have'been developed1,9, the preparation of optically pure material still involves resolution methods requiring chiral auxiliary reagents1,lO. We wish to report here the application of enzymatic methodize on the preparation of both enantiomers of 'I-oxanorbornane derivatives.
RRSULTB AND DISCUSSION Synthe~ir of Subztrates 'I-Oxabicyclol2.2.ilhept-S-en-?-one (1) was synthezized according to the method of Black and Vogel'. Sodium borohydride reduction at low temperature led to the ucluzive forration of ezd+alcohol 212#13. R8terification with 14 butyxic acid anhydrido following a ztandard proceduxo gave ester 3 which was 15,16 expected fxcm &revfouz experiences to be well suited for' eizymatic resolutfen. St&orpecific nodificatioz of the double bond in substrate 3 to obtain the hi&r functionalizod &b&rate 5 wae accomplished by ozzdua tetroxitiac&alyxed cfm-dihydmxyl.tiaA1' and 8tabzequenttranzacet.alltiUon of the crude dial 4. 389
390
R. SAPet al.
SCHW
I: Synthesis of substrates6.
1 ;$j"
" G',
5
3
2
R’
H
-co-wH2p~
4
3
-CO-KH2)2CHI
-CCNH2)2CH~
Ii
:>=c(ctls)2
I;:C(CH+2
R2
OH
6
ir NaBW, MeOH. ii: (n-0IV-CO)rO/PyfD)IAP, CIWD. iii4 N-methylmorpholineN-oxide*lDO/OeW, acetone. iv, 2,2-dimethoxy$ropdne/H-. VI NaOMe/MeOH. Enzymatic
Bxperimente
For the enzymatic resolution of substrates 3 and 5 using lipase from 18,19 a strategy previously described15,16 was applied: The Candfda cylindracea course of hydrolysis rpasmonitored by consumption of 1N sodium hyckoxide using a pH-stat2' and was stopped at an appropriate point to obtain an optimum in chemical and optical yield of products21 E40% conversion for alcohols (2*,6*) and 60% for the corresponding ent-esters (ent-3*,ent-S*)]. SCHNHN II: Knzymatic remolution6.
UC-3
CandikclJ~e4z lipase
c
2'
+
e&-3*
+
et&-s*
A &G Rb
TAELN Ia Nnantiomei-icexcems of products. Substrate
Cmvermim Product
laolateda 3
P
5
&.*
e.e.
a?
[Zl
[*I
9w
+I42
Wf
Emmaim
bo%
-Y.O
c
broduct
"lib
[g/100
e&-3-
2.29 16.1
ieolsts8
'
u&r
e.e.
60% 20 OD
[Xl
[Ol
)97'
-149
d'g
4.2
c cgm?o
nd
6.58 lb.J
a: For abmolutfbcopfiguration mee lchmm I and II‘. br CHCla lolutioq. Determined by P-NMN spectroscopy of the mA-ester. dr Detetined by H-g spectromcopy using Nu(hfc)m. er Determined by nteasur~t.of,optlcal rotation aft= transesterification to the corresponding alcohol.ent-2 fr Determined by F4!4R spectrorcopy of $JreIPlVA-eater after trkr&&erif&ation to the correeponding alcohol ent-6 . gt Determined by m*(~s wt?.of opFica1 rotation by comparison with material independently synthesized f&m ent-3 .
391
7-Oxabicyclo[2.2.l]hqxacptanc derivatives AE shown in table I both substrates are hydrolyzed enzymatically with high enantioepecif,ity. To determine the absolute configuration of products alcohol 22 to give ketone l* whore absolute 2* was oxidized by Swern oxidation configuration ia uell establiehed'. Rnt-S* was correlated via aenae and magnitude of optical rotation with material independently eynthesired from m&-3*.
_.. An attempt to hydrolyze enantiospecificallycyanoester 72', itself being a 24 was precursor in the eyntheeie of 11, using lipaze from A~pergfllus 8~. unsuccessful: Although the acetoxy moiety of 7 was readily cleaved, liberating '1 which in turn could be converted to ketone ent-1 , the cyanohydrin ent-8*, enantiomeric exceee'did not exceed 20%. SCHEMP 1111 Enzymatic hydrolyeie of cyanoeeter 7. 0
Ax
CM
ww?-
11pS3e
WX-1
4
0
0
CM
eat-
NaOMdMeOH CHyO
lP
-4
0 ent-
I*
EXPERIMXNTAL
Helting points are uncorrected. Optical r,otatQne were wsured on a Perkin F-NMR spectra w8re Elmer 141 polarimeter in CHClz solution. Ii-, C- and recorded in CDClz on a Bruker Wfi 90 spectrometer. Chemical shifts are reported t-triplet and in 6 from TUS ae internal standard. emsinglet, ddublet, mloultfplet. GLC analyeee were performed on a Dani 8500 chromatograph equipped with FID using a 25 m capillary column (CP-sil-5 CB). Elemental analyses H, N) for all novel compounds were within 0.4% of calculated values. COlk chromatography wa8 performed on Merck 60 silica gel. Syntheria
of rub&rater
(lRS,2RS,4RS)-7-Oxabicyclo~2.2.11hept-5-en-2-o1(2): Reduction of ketone l* using NaBW in MeOH p& O-5 C (internal temperature) following a procedure previously describe$ yielded,719 of,l. p exe-alcohol could be detected by GLC-analysis. Mp 25 C, bp 94-9 C/lOmm . ?I-NMR: 0,92(dd, J-2.5 and 12H2, lH), 2.03-2.35(m, lH), 3.15(6, lH, IZO-exchangeable), 4.23-4.46(m, lH), A;4&98(m, ZH), 6.3O(dd, J=1.5 and 6H2, lH), 6.57(dd, Jp1.5 and 6H2, 1H). : 35.9(C-3), 68.8(C-2), 79.5 and 79.7(C-1 and C-4), 132.O(C-6), 137.O(C-5). (lRS,2RS,4RS)-7-Gxablcyclo[ 2.2.l]hept-5-en-a-y1 butyrate (3): &terification of 3 using butyricoacid anheride following a standard procedure gave 94% of eater 3. Bp 112-4 C/llzza. H-NHR: 0.97(t, J=7Hz, 3H), 1.38-1.78(m, 2H), 2.00-2.47(m, 4H), 4.81(dd, J-l.5 and 7H2, lH), 4.88-5.03(m, 2H), 6.02(d, J=6Hz, lH), 6.34(dd, J-1.5 and 6Hz, 1H). (lRS,2RS,6SR,7RS,8RS)-4,4-Dinuthyl-3,5,10-trioxatricycloC 5.2.1.0x'dldec-8-yl butyrate (5): cis-D&hydroxylation using N-methylmorpholine-N-oxide-Hz0 and cat. OeOI in acetone and aubeecuent transacetaliaationof the crude diol 4 in 2,2-dimethoxypropane/p-toluexieaulfo&c ac$Q.TO as described in ref. 15 led to dioxolane 5 in 53% yield. Bp 130-40 C/2mm . H-NMR: 0.91(t, J=7Hz, 3H), 1.13-1.85(m, 4H), 1.35(8, 3H), 1.52(s, 3H), 2.10-2.52(m, 3H), 4.35(d, J=SHz, lH), 4.48(d, J=2Hz, lH), 4.57(m, lH), 4.74(d, J=SHz, lH), 4.87-5.17(m, 1H). (lRS,2RS,6SR,7W,8RS)-4,4-DiUthyl-3,5,lO-trio~~~~~lo~
5.2.1.0"d]docan-8-ol transezteri&ication Mp 105-7 C (i
R. Sls et al.
392
ltnrymnticresolution To a solution of lipase from Csndida cylindracea""O (2.5g) in phosphate buffer (O:lN), psi7.2, 25Oml) was added substrate ester 3 (20.0s) or 5 (lO.Og); Whiie vigorous stirring was maintained the pH was kept‘ constant at 1.2 by addition of N NaOH from an autoburette, When the appropriate degrge of conversion was accomplished (40% for 2 and 6 , 60% for ent-3 and ent-9,) the products were extracted with ClbCls. Kvaporatiop of vganic solvents and subsequent cqlumn chrox+ography gave alcohols 2 and 6 (70-80% yield) and esters ent-3 and ent-5 (SO-900 yield).
ACKNOWLEDGEMENT
The authors wish to express their cordial thanks to Amano Pharm.Co.Ltd. and Meito Sangyo Co.Ltd. (both Japan) who kindly provided the enrymes. This work was supported by Fonda zur wrderung der wissenechaftlichen Forschung (project no. 6030). REFERENCE8
: 3a
b 4 :
; 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
AND
NOTES
K.A.Black and P.Vogel, Helv.Chfm.Acta 67, 1612 (1984). A.Warm and P.Vogel, J.Org.Cben1.51,5348 (1986). A.Wann and P.Vogel, Tetrahedron Lett. 1986, 5615. A.Warm and P.Vogel, Helv.Chim.Acta 70, 690 (1987). A.Warm and P.Vogel, Tetrahedron Lett. 1985, 5127. K.R.Schmidt, C.Beitske and A.K.Porrest, J.Chem.Soc.,Chem.Conmun.909,1982. Throughout this paper all enantiomerically enriched compounds are designated with an asterisk (*), the other enantiomer is indicated by the prefix "ent". Compounds without it are racemic. The absolute configuration of the enantfomer drawn in scheme I corresponds to the starred series. P.-A.CarruDt and P.Voael. Tetrahedron L-ett.1986, 5505. K.A.Black and P.Vogel; J~Org.Chesf.51,5341 (1986). E.Vieira and P.Voqel, ?ielv.Chixn.Acta 65, 1700 (1982). E.Vieira and P.Vo⪙ Helv.Chfm.Acta 66. 1865 i1983i. 3351 (1986): ' ' J.B.Jones, TetraJ&&42, J.Woursounidis and D.Weae, Aust.J.Chem.36, 2473 (1983). Dn preparations of comp&nds 1 and 2 all solvents were removed by distillation at atmospheric pressure since the products exhibited a remarkable volatility upon evaporation in vacua. G.tifle, W.Steglich and H.VorbrQggen, Angew.CAem.90, 602 (1978); Int.Ed.Engl.17, 569 (1978). Th.Oberhauser, M.Bodenteich, K.Paber, G.Penn and Ii.Griengl,Tetrahedron, in press (1987). G.Eichberger, G.Penn, K.Faber and H.Griengl, Tetrahedron Lett. 1986, 2843. V.Van Rheenan, R.C.Kelly and D.Y.Cha, Tetrahedron Lett.1976, 1973. Lipase MY, 30,000 u/g, obtained from Weito Sangyo Co.Ltd. Lipase from Pseudomonas sp. (Lipase P, 31,000 u/g, obtained from Amano Phann.Co.Ltd.) was unable to cleave esters 3 and 5. J.B.Jones and'Y.Y.Lin, Can.J.Chem.50, 2053 (1972): C.-S.Chen. Y.Pulimoto, G.Girdaukas and C.J.Sih, J.Am.C!hem.Soc.lO4,7294 (1982). . A.J.Mancuso and D.Swern, Syntieafs 1981, 165. For a similar conversion see: N.Watsuo and N.Ohno, Tetrahedron Lett.1985, 5533. Lipase AP6, 60,000 u/g, obtained from Amano Pharm.Co.Ltd. Kugelrohr distillation.
mmkdrm~ vol. 44. No. 2, pp. 389 to 39Z1988 Printed in Great Britain.
WZYMATIC PREPARATION OF OPTICALLY ACTIVZ 'I-OZARICYCLO[ 2.2.13RZPTANZ DERIVATIVES
R.Saf, K.Faber,
G.Penn and H.Griengl*
Institute of Organic Chemistry, Technical Dnfverzity Graz, Stremayrgazse 16, A-0010 Gxaz, Austria (Receiaed in Germany 2 1September 1987)
endo-7-oxabicyclo - Enzymatic resolution of hept-2-yl'butyratea 3 aud 5 wing lipaze from bicyclic Candfde cylfndracea led to optically alcohols and e&era being impcwtant inteskm for the eynthesi~~of biologically active compounda.
INTRODUCTION 7-Oxabicyclol2.2.11heptane derivatives have gained increasing importance as starting material for the preparation of "naked sugars"1,2 themselves being valuable intermediates for the syntheeiz of biologically active compounds such 2,4 and C-nucleoeides5 . Their versatility as as nonactic acid3, dsiinozamine synthetic tools has recently been demonstrated by regio- and stereospecific functionalisation of 'I-oxabicyclol2.2.11hept-5-en-a-one (1)6 Qwolving carbon atoms C-27, C-33 and C-S/C-6*. Although practical and efficient syntheses for racemic ketone 1 have'been developed1,9, the preparation of optically pure material still involves resolution methods requiring chiral auxiliary reagents1,lO. We wish to report here the application of enzymatic methodize on the preparation of both enantiomers of 'I-oxanorbornane derivatives.
RRSULTB AND DISCUSSION Synthe~ir of Subztrates 'I-Oxabicyclol2.2.ilhept-S-en-?-one (1) was synthezized according to the method of Black and Vogel'. Sodium borohydride reduction at low temperature led to the ucluzive forration of ezd+alcohol 212#13. R8terification with 14 butyxic acid anhydrido following a ztandard proceduxo gave ester 3 which was 15,16 expected fxcm &revfouz experiences to be well suited for' eizymatic resolutfen. St&orpecific nodificatioz of the double bond in substrate 3 to obtain the hi&r functionalizod &b&rate 5 wae accomplished by ozzdua tetroxitiac&alyxed cfm-dihydmxyl.tiaA1' and 8tabzequenttranzacet.alltiUon of the crude dial 4. 389
390
R. SAPet al.
SCHW
I: Synthesis of substrates6.
1 ;$j"
" G',
5
3
2
R’
H
-co-wH2p~
4
3
-CO-KH2)2CHI
-CCNH2)2CH~
Ii
:>=c(ctls)2
I;:C(CH+2
R2
OH
6
ir NaBW, MeOH. ii: (n-0IV-CO)rO/PyfD)IAP, CIWD. iii4 N-methylmorpholineN-oxide*lDO/OeW, acetone. iv, 2,2-dimethoxy$ropdne/H-. VI NaOMe/MeOH. Enzymatic
Bxperimente
For the enzymatic resolution of substrates 3 and 5 using lipase from 18,19 a strategy previously described15,16 was applied: The Candfda cylindracea course of hydrolysis rpasmonitored by consumption of 1N sodium hyckoxide using a pH-stat2' and was stopped at an appropriate point to obtain an optimum in chemical and optical yield of products21 E40% conversion for alcohols (2*,6*) and 60% for the corresponding ent-esters (ent-3*,ent-S*)]. SCHNHN II: Knzymatic remolution6.
UC-3
CandikclJ~e4z lipase
c
2'
+
e&-3*
+
et&-s*
A &G Rb
TAELN Ia Nnantiomei-icexcems of products. Substrate
Cmvermim Product
laolateda 3
P
5
&.*
e.e.
a?
[Zl
[*I
9w
+I42
Wf
Emmaim
bo%
-Y.O
c
broduct
"lib
[g/100
e&-3-
2.29 16.1
ieolsts8
'
u&r
e.e.
60% 20 OD
[Xl
[Ol
)97'
-149
d'g
4.2
c cgm?o
nd
6.58 lb.J
a: For abmolutfbcopfiguration mee lchmm I and II‘. br CHCla lolutioq. Determined by P-NMN spectroscopy of the mA-ester. dr Detetined by H-g spectromcopy using Nu(hfc)m. er Determined by nteasur~t.of,optlcal rotation aft= transesterification to the corresponding alcohol.ent-2 fr Determined by F4!4R spectrorcopy of $JreIPlVA-eater after trkr&&erif&ation to the correeponding alcohol ent-6 . gt Determined by m*(~s wt?.of opFica1 rotation by comparison with material independently synthesized f&m ent-3 .
391
7-Oxabicyclo[2.2.l]hqxacptanc derivatives AE shown in table I both substrates are hydrolyzed enzymatically with high enantioepecif,ity. To determine the absolute configuration of products alcohol 22 to give ketone l* whore absolute 2* was oxidized by Swern oxidation configuration ia uell establiehed'. Rnt-S* was correlated via aenae and magnitude of optical rotation with material independently eynthesired from m&-3*.
_.. An attempt to hydrolyze enantiospecificallycyanoester 72', itself being a 24 was precursor in the eyntheeie of 11, using lipaze from A~pergfllus 8~. unsuccessful: Although the acetoxy moiety of 7 was readily cleaved, liberating '1 which in turn could be converted to ketone ent-1 , the cyanohydrin ent-8*, enantiomeric exceee'did not exceed 20%. SCHEMP 1111 Enzymatic hydrolyeie of cyanoeeter 7. 0
Ax
CM
ww?-
11pS3e
WX-1
4
0
0
CM
eat-
NaOMdMeOH CHyO
lP
-4
0 ent-
I*
EXPERIMXNTAL
Helting points are uncorrected. Optical r,otatQne were wsured on a Perkin F-NMR spectra w8re Elmer 141 polarimeter in CHClz solution. Ii-, C- and recorded in CDClz on a Bruker Wfi 90 spectrometer. Chemical shifts are reported t-triplet and in 6 from TUS ae internal standard. emsinglet, ddublet, mloultfplet. GLC analyeee were performed on a Dani 8500 chromatograph equipped with FID using a 25 m capillary column (CP-sil-5 CB). Elemental analyses H, N) for all novel compounds were within 0.4% of calculated values. COlk chromatography wa8 performed on Merck 60 silica gel. Syntheria
of rub&rater
(lRS,2RS,4RS)-7-Oxabicyclo~2.2.11hept-5-en-2-o1(2): Reduction of ketone l* using NaBW in MeOH p& O-5 C (internal temperature) following a procedure previously describe$ yielded,719 of,l. p exe-alcohol could be detected by GLC-analysis. Mp 25 C, bp 94-9 C/lOmm . ?I-NMR: 0,92(dd, J-2.5 and 12H2, lH), 2.03-2.35(m, lH), 3.15(6, lH, IZO-exchangeable), 4.23-4.46(m, lH), A;4&98(m, ZH), 6.3O(dd, J=1.5 and 6H2, lH), 6.57(dd, Jp1.5 and 6H2, 1H). : 35.9(C-3), 68.8(C-2), 79.5 and 79.7(C-1 and C-4), 132.O(C-6), 137.O(C-5). (lRS,2RS,4RS)-7-Gxablcyclo[ 2.2.l]hept-5-en-a-y1 butyrate (3): &terification of 3 using butyricoacid anheride following a standard procedure gave 94% of eater 3. Bp 112-4 C/llzza. H-NHR: 0.97(t, J=7Hz, 3H), 1.38-1.78(m, 2H), 2.00-2.47(m, 4H), 4.81(dd, J-l.5 and 7H2, lH), 4.88-5.03(m, 2H), 6.02(d, J=6Hz, lH), 6.34(dd, J-1.5 and 6Hz, 1H). (lRS,2RS,6SR,7RS,8RS)-4,4-Dinuthyl-3,5,10-trioxatricycloC 5.2.1.0x'dldec-8-yl butyrate (5): cis-D&hydroxylation using N-methylmorpholine-N-oxide-Hz0 and cat. OeOI in acetone and aubeecuent transacetaliaationof the crude diol 4 in 2,2-dimethoxypropane/p-toluexieaulfo&c ac$Q.TO as described in ref. 15 led to dioxolane 5 in 53% yield. Bp 130-40 C/2mm . H-NMR: 0.91(t, J=7Hz, 3H), 1.13-1.85(m, 4H), 1.35(8, 3H), 1.52(s, 3H), 2.10-2.52(m, 3H), 4.35(d, J=SHz, lH), 4.48(d, J=2Hz, lH), 4.57(m, lH), 4.74(d, J=SHz, lH), 4.87-5.17(m, 1H). (lRS,2RS,6SR,7W,8RS)-4,4-DiUthyl-3,5,lO-trio~~~~~lo~
5.2.1.0"d]docan-8-ol transezteri&ication Mp 105-7 C (i
R. Sls et al.
392
ltnrymnticresolution To a solution of lipase from Csndida cylindracea""O (2.5g) in phosphate buffer (O:lN), psi7.2, 25Oml) was added substrate ester 3 (20.0s) or 5 (lO.Og); Whiie vigorous stirring was maintained the pH was kept‘ constant at 1.2 by addition of N NaOH from an autoburette, When the appropriate degrge of conversion was accomplished (40% for 2 and 6 , 60% for ent-3 and ent-9,) the products were extracted with ClbCls. Kvaporatiop of vganic solvents and subsequent cqlumn chrox+ography gave alcohols 2 and 6 (70-80% yield) and esters ent-3 and ent-5 (SO-900 yield).
ACKNOWLEDGEMENT
The authors wish to express their cordial thanks to Amano Pharm.Co.Ltd. and Meito Sangyo Co.Ltd. (both Japan) who kindly provided the enrymes. This work was supported by Fonda zur wrderung der wissenechaftlichen Forschung (project no. 6030). REFERENCE8
: 3a
b 4 :
; 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
AND
NOTES
K.A.Black and P.Vogel, Helv.Chfm.Acta 67, 1612 (1984). A.Warm and P.Vogel, J.Org.Cben1.51,5348 (1986). A.Wann and P.Vogel, Tetrahedron Lett. 1986, 5615. A.Warm and P.Vogel, Helv.Chim.Acta 70, 690 (1987). A.Warm and P.Vogel, Tetrahedron Lett. 1985, 5127. K.R.Schmidt, C.Beitske and A.K.Porrest, J.Chem.Soc.,Chem.Conmun.909,1982. Throughout this paper all enantiomerically enriched compounds are designated with an asterisk (*), the other enantiomer is indicated by the prefix "ent". Compounds without it are racemic. The absolute configuration of the enantfomer drawn in scheme I corresponds to the starred series. P.-A.CarruDt and P.Voael. Tetrahedron L-ett.1986, 5505. K.A.Black and P.Vogel; J~Org.Chesf.51,5341 (1986). E.Vieira and P.Voqel, ?ielv.Chixn.Acta 65, 1700 (1982). E.Vieira and P.Vo⪙ Helv.Chfm.Acta 66. 1865 i1983i. 3351 (1986): ' ' J.B.Jones, TetraJ&&42, J.Woursounidis and D.Weae, Aust.J.Chem.36, 2473 (1983). Dn preparations of comp&nds 1 and 2 all solvents were removed by distillation at atmospheric pressure since the products exhibited a remarkable volatility upon evaporation in vacua. G.tifle, W.Steglich and H.VorbrQggen, Angew.CAem.90, 602 (1978); Int.Ed.Engl.17, 569 (1978). Th.Oberhauser, M.Bodenteich, K.Paber, G.Penn and Ii.Griengl,Tetrahedron, in press (1987). G.Eichberger, G.Penn, K.Faber and H.Griengl, Tetrahedron Lett. 1986, 2843. V.Van Rheenan, R.C.Kelly and D.Y.Cha, Tetrahedron Lett.1976, 1973. Lipase MY, 30,000 u/g, obtained from Weito Sangyo Co.Ltd. Lipase from Pseudomonas sp. (Lipase P, 31,000 u/g, obtained from Amano Phann.Co.Ltd.) was unable to cleave esters 3 and 5. J.B.Jones and'Y.Y.Lin, Can.J.Chem.50, 2053 (1972): C.-S.Chen. Y.Pulimoto, G.Girdaukas and C.J.Sih, J.Am.C!hem.Soc.lO4,7294 (1982). . A.J.Mancuso and D.Swern, Syntieafs 1981, 165. For a similar conversion see: N.Watsuo and N.Ohno, Tetrahedron Lett.1985, 5533. Lipase AP6, 60,000 u/g, obtained from Amano Pharm.Co.Ltd. Kugelrohr distillation.