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The first substituted boranonucleic acids: a novel synthetic route
Inorganic Chemistry Communications 4 (2001) 629±631
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The ®rst substituted boranonucleic acids: a novel synthetic route Kamesh Vyakaranam a, Geeta Rana a, Bernard F. Spielvogel b, Narayan S. Hosmane a
a,*
Department of Chemistry and Biochemistry, The Michael Faraday Laboratories, Northern Illinois University, DeKalb, IL 60115-2862, USA b Metallo-Biotech International, Inc., 663 Teal Court, DeKalb, IL 60115-6201, USA Received 12 July 2001; accepted 31 July 2001
Abstract Diethylchlorophosphite-cyanoborane (1) was prepared in 65% yield by the reaction of sodium cyanoborohydride and bromine followed by re¯uxing with diethylchlorophosphite. Compound 1 was reacted further with several commercially available nucleosides to give substituted boranonucleic acids in 46±91% yields. Ó 2001 Elsevier Science B.V. All rights reserved. Keywords: Boranophosphate; Borane; Cyanoboranes; Nucleic acids; Derivatized boranes
There is increasing evidence that boron containing biomolecules can play a much greater role in the areas of life sciences such as pharmacology, medicine, biochemistry and nutrition than previously thought and, consequently, it has been shown in model studies that boron analogues of amino acids, nucleosides and nucleic acids have potent anti-cancer, anti-in¯ammatory, hypolipidemic, anti-osteoporotic, anti-viral, and other promising pharmacological activity [1]. Furthermore, important new diagnostic applications have been reported in the areas of PCR sequencing and DNA diagnostics using boronated DNA [2]. Substitution of a hydride with amine in the boranocarbonate structure would produce isoelectronic and isostructural analogues of the a-amino acids. Synthetic methodologies were developed and led to the ®rst boronated analog of glycine, H3 NBH2 C(O)OH with a pKa for the carboxylic proton of 8.3, some six log units higher than the analogous proton in glycine [3]. The incorporation of BH3 moiety in these species led to signi®cant problems in the chemical synthesis of boronated DNA in which highly reducing borane in¯uenced base-degradation. Consequently, base-degradation has been observed in all of the known boronated nucleosides except the one with the base, thymidine [4]. In addition, base-borane adducts of the nucleosides are generally quite toxic due to the presence of the borane * Corresponding author. Tel.: +1-815-753-3556; fax: +1-815-7534802. E-mail address: [email protected] (N.S. Hosmane).
moiety. Thus, borohydrides, boranocarbonates, and amine-boranes typically have LD50 values in the tens of mg/kg by intraperitoneal (IP) injection in mice. However, substitution of hydride, with ammonia as in the boron analog of glycine, H3 NBH2 COOH, produces a compound of very low toxicity, LD50 >2000 mg/kg [5]. In view of the above noted problems that are associated with the underivatized borane unit linked to the phosphorus in the phosphodiester backbone, we have embarked on an intensive eort in replacing the BH3 unit with much less toxic and less reducing moiety, such as derivatized boranes, BH2 X (X COOH, COOR, C(O)NHR, CN, etc.) [6]. Here we report hitherto unknown nucleosides incorporating derivatized borane moiety such as diethylchlorophosphite-cyanoborane (1), 50 -(diethylphosphite-cyanoborano)-30 , N6 -o-dibenzoyl20 -deoxyadenosine (2a), 50 -(diethylphosphite-cyanoborano)-30 -acetylthymidine (2b), 50 -(diethylphosphite0 2 cyanoborano)-3 -acetyl-N -isobutryl-20 -deoxyguanosine (2c), 50 (-diethylphosphite-cyanoborano)-30 , N4 -dibenzoyl-20 -deoxycytidine (2d), that are envisioned to exhibit properties ideal for use as new therapeutics. Diethylchlorophosphite-cyanoborane (1) was prepared in 65% yield by the reaction of sodium cyanoborohydride and bromine followed by re¯uxing with diethylchlorophosphite as a colorless oil (Scheme 1) that decomposed at 107 °C [7]. The proton-decoupled 11 B NMR spectra showed a doublet at d 42.18 ppm and the proton-decoupled 31 P NMR spectra showed a quartet at d 90.2 ppm that are consistent with the molecular geometry of 1. The IR spectra showed two
1387-7003/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 1 3 8 7 - 7 0 0 3 ( 0 1 ) 0 0 2 8 9 - 1
630
K. Vyakaranam et al. / Inorganic Chemistry Communications 4 (2001) 629±631
NaBH3CN
Br2 / DME
OEt
OEt EtO P Cl (BH2CN)X
P
EtO
DME
Cl
BH2CN 1 OEt
HO
P
EtO
1. 1
B
O
OR 2a 2b 2c 2d
NHBz
B=
N 2a = Ade
N H
R = Bz R = Ac R = Ac R = Bz NHBz
O
O N
N
B
O BH2CN
2. Et3N
OR
O
N
O
N
HN
NH
Buti-HN
2b = Thy
N
N H
2c = Gua
N N
O
2d = Cyt
Scheme 1.
singlets, at 2470 and 2395 cm 1 due to BH stretches and the one at 2192 cm 1 was assigned to a C±N bond. This compound was hydrolytically stable for few days but slowly decomposed to dimethylphosphate over a period of days. The borano-phosphate nucleosides (2(a±d)) were prepared by the reaction of 1 with suitable 30 protected nucleosides according to Scheme 1 [8]. The reactions were carried out in anhydrous THF at room temperature using one equivalent of triethyl amine that was used to quench the hydrogen chloride produced during the reaction. The nucleosides were obtained as colorless oils by puri®cation using ¯ash chromatography on silica gel with a solvent mixture of ethyl acetate:hexane (9:1). The yields obtained were 91%, 47%, 46% and 88%, for the deoxy-adenosine, deoxy-thymidine, deoxyguanosine and deoxy-cytidine derivatives, respectively. The yields for the deoxy-thymidine and deoxy-guanosine derivatives were less and were expected due to degradation of the compounds during the puri®cation process. All compounds were characterized by IR spectra, 1 H, 11 B and 13 C NMR spectra and elemental analysis. The most important information, that were found in the spectra, are worthy of further comments; for example, the proton-decoupled 31 P NMR spectra of (2(a±d)) showed a quartet corresponding to a cyanoborane phosphate group in each molecule [9]. The protondecoupled 11 B NMR spectrum of each corresponding species contained a doublet due to the cyanoborane phosphate group [9]. The IR spectra of each compound showed two singlets; one for the BH unit and another as a broad singlet for a CN moiety. The formulations of compounds (2(a±d)) are further supported by their mi-
croanalytical data [8]. The 13 C NMR spectra of 1 and (2(a±d)) showed no surprises and, therefore, deserve no special comments. This work presents the ®rst report on a novel phosphitylating agent and a set of boronated nucleosides. Nevertheless, further exploration of these species in the nucleic acid backbone modi®cation is therefore warranted in order to greatly increase the scope and application of this novel class of nucleic acids. The pharmacological properties and further chemistry of these compounds are currently underway in our laboratories. Acknowledgements This work was supported by grants from the National Science Foundation (CHE-9988045), the donors of the Petroleum Research Fund, administered by the American Chemical Society, and Northern Illinois University through Presidential Research Professorship (to NSH). References [1] [a] A. Hasan, H. Li, J. Tomasz, B.R. Shaw, Nucl. Acid Res. 24 (1996) 2150±2157; [b] H. Li, K. Porter, F. Huang, B.R. Shaw, Nucl. Acid Res. 23 (1995) 4495±4501; [c] A. Sood, B.R. Shaw, B.F. Spielvogel, J. Am. Chem. Soc. 112 (1990) 9000±9001; [d] A. Sood, B.F. Spielvogel, B.R. Shaw, J. Am. Chem. Soc. 111 (1989) 9234±9235;
K. Vyakaranam et al. / Inorganic Chemistry Communications 4 (2001) 629±631
[2] [3] [4]
[5] [6]
[7]
[8]
[e] B.F. Spielvogel, A. Sood, J. Tomasz, B.R. Shaw, S. Karthikeyan, Neutron Capture Ther. (1993) 361±365; [f] I.H. Hall, E.S. Hall, L. Chi, B.R. Shaw, A. Sood, B.F. Spielvogel, Anticancer Res. 12 (1992) 1091±1098; [g] A. Sood, B.R. Shaw, B.F. Spielvogel, E.S. Hall, L.K. Chi, I.H. Hall, Pharmazie 47 (1992) 833±838; [h] J. Tomasz, B.R. Shaw, K.W. Porter, B.F. Spielvogel, A. Sood, Angew. Chem. Int. Ed., Engl. 31 (1992) 1373±1375. K.W. Porter, J.D. Briley, B.R. Shaw, Nucl. Acid Res. 25 (1997) 1611±1617. K.H. Scheller, B.R. Martin, B.F. Spielvogel, A.T. McPhail, Inorg. Chim. Acta 57 (1982) 227. [a] B.F. Spielvogel, A. Sood, B.R. Shaw, I.H. Hall, R.G. Fairchild, B.H. Laster, C. Gordon, Prog. Neutron Capture Ther. Cancer (1992) 211±213; [b] A.P. Higson, A. Sierzchala, H. Brummel, Z. Zhao, M.H. Caruthers, Tetrahedron Lett. 39 (1998) 3899±3902. B.F. Spielvogel, M.K. Das, A.T. McPhail, K.D. Onan, I.H. Hall, J. Am. Chem. Soc. 102 (1980) 6343±6344. [a] A.T. McPhail, K.D. Onan, B.F. Spielvogel, P. Wisian-Neilson, J. Chem. Res. (1978) 205; [b] P. Wisian-Neilson, M.K. Das, B.F. Spielvogel, Inorg. Chem. 17 (1978) 2327±2329; [c] B.F. Spielvogel, F. Harchelroad, P. Wisian-Neilson, J. Inorg. Nucl. Chem. 41 (1979) 1223±1227. Bromine (6.24 g, 39.9 mmol) was added drop-wise with stirring to a solution of sodium cyanoborohydride (5 g, 79.0 mmol) in anhydrous dimethoxy ethane (80 ml). The ®ltrate was mixed with diethylchlorophosphite (12.52 g, 80 mmol) under nitrogen and heated at re¯ux for 2 days. After ®ltration the solvent was removed under reduced pressure to give an oil. The oil was dissolved in ether (50 ml), washed with pentane (3´50 ml) and the solvent was removed under reduced pressure to give diethylchlorophosphitecyanoborane (1) as colorless oil in 65% yield 1 H NMR (200 MHz, DMSO reference to TMS): d 1.34 (t, 6H, CH3 ), 4.22 (m, 4H, CH2 ); 13 C NMR (50.32 MHz; DMSO reference to TMS): d 17.5 (CH3 ), 63.7 (OCH2 ); 31 P NMR (81.01 MHz; DMSO reference to H3 PO4 ): d 90.2 (q of t, JPB 141.80 Hz, JPH unresolved); 11 B NMR (64.21 MHz; DMSO reference to BF3 áOEt2 ) d 42.18 (t of d, JBP 139.6 Hz, JBH 99.52 Hz); IR (KBr pellet) 2470, 2395 cm 1 m(BH); 2192 cm 1 m(CN); Anal. calcd for C5 H12 O2 NBPCl: C, 30.42; H, 6.09; N, 7.09. Found: C, 31.01; H, 5.99; N, 6.98. N6 , 30 -o-Dibenzoyl-20 -deoxyadenosine (10.0 mg, 0.06 mmol), 30 acetylthymidine (0.35 g, 1.24 mmol), N2 -isobutryl-30 -acetyl-20 deoxyguanosine (50.0 mg, 0.13 mmol), or N4 , 30 -o-dibenzoyl-20 deoxycytidine (25.0 mg, 0.06 mmol), respectively, diethylchlorophosphite-cyanoborane (12.0 mg, 0.06 mmol), (0.24 g, 1.24 mmol), (26.0 mg, 0.13 mmol) and (12.0 mg, 0.06 mmol), respectively and triethylamine (6.0 mg, 0.06 mmol), (0.5 mg, excess), (13.3 mg, 0.13 mmol), (6.0 mg, 0.06 mmol), respectively, were dissolved in anhydrous THF and the mixture was stirred at room temperature for 6 h. After ®ltration to remove insoluble materials, the solvent was removed under reduced pressure. The residue was taken up in dichloromethane (20 ml) and was washed with water (5´15 ml). The organic layer was dried, ®ltered and concentrated under reduced pressure. The residue was puri®ed by ¯ash chromatography on silica gel using ethyl acetate: hexane (9:1) to give 50 -(diethylphosphite-cyanoborano)-30 , N6 -o-dibenzoyl-20 deoxyadenosine (2a, 31 mg, 90.7%, anal. calcd. for C29 H32 O7 N6 BP: C, 56.09; H, 5.16; N, 13.54. Found: C, 55.89; H, 5.09;
631
N, 13.01), 50 -(diethylphosphite-cyanoborano)-30 -acetylthymidine (2b, 260 mg, 46.5%, anal. calcd. for C17 H27 O8 N3 BP: C, 45.82; H, 6.06; N, 9.43. Found: C, 45.74; H, 5.98; N, 9.01), 50 -(diethylphosphite-cyanoborano)-30 -acetyl-N2 -isobutryl-20 -deoxyguanosine (2c, 35 mg, 45.8%, anal. calcd. for C21 H32 O8 N6 BP: C, 46.64; H, 5.92; N, 15.55. Found: C, 46.02; H, 5.81; N, 15.12) and 50 (diethylphosphite-cyanoborano)-30 , N4 -dibenzoyl-20 -deoxycytidine (2d, 28 mg, 87.7%, anal. calcd. for C28 H32 O8 N4 BP: C, 56.35; H, 5.37; N, 9.39. Found: C, 55.99; H, 5.24; N, 10.01) as colorless oil, respectively. [9] The spectroscopic data for 2a: 1 H NMR (200 MHz, DMSO reference to TMS): d 1.39, 1.40 (t, 6H, CH3 ), 1.0±1.6 (br, 2H, BH2 ), 2.41±2.6 (m, 2H, H-20 ), 3.2 (s, 3H, OCH3 ), 3.91±4.12 (m, 2H, H-50 ), 4.12±4.14 (m, 1H, H-40 ), 4.26 (m, 4H, OCH2 ), 4.81±5.0 (m, 1H, H30 ), 6.46 (m, 1H, H-10 ), 8.11 (s, 1H, H-8), 8.35 (s, 1H, H-2), 8.62 (m, 5H, Ar±H), 9.01 (br, s, NH); 13 C NMR (50.32 MHz; DMSO reference to TMS): d 14.4 (CH3 ), 17.3 (CH2 ), 60.4 (OCH2 ), 58.1, 56.3 (OCH), 53 (OCH3 ), 129 (C±Ar), 170.7 (C@O); 31 P NMR (81.01 MHz; DMSO reference to H3 PO4 ): d 89.7 (q of t, JPB 161.20 Hz, JPH unresolved); 11 B NMR (64.21 MHz; DMSO reference to BF3 áOEt2 ) d 41.8 (t of d, JBP 169.4 Hz, JBH 111.95 Hz); IR (KBr pellet) 2408, 2359 cm 1 m(BH); 2200 cm 1 m(CN). 2b: 1 H NMR (200 MHz, DMSO reference to TMS): d 1.41, 1.44 (t, 6H, CH3 ), 1.0±1.8 (br, 2H, BH2 ), 1.95 (s, 3H, CH3 ), 2.30±2.41 (m, 2H, H-20 ), 3.2 (s, 3H, OCH3 ), 4.18±4.24 (m, 2H, H50 ), 4.13±4.15 (m, 1H, H-40 ), 4.28 (m, 4H, OCH2 ), 5.26 (m, 1H, H30 ), 6.41 (m, 1H, H-10 ), 6.71 (s, 1H, H-3), 7.36 (d, 1H, H-6), 9.21 (br, s, NH); 13 C NMR (50.32 MHz; DMSO reference to TMS): d 14.2 (CH3 ), 18.4 (CH2 ), 60.9 (OCH2 ), 57.9, 56.1 (OCH), 52.8 (OCH3 ), 169.7 (C@O); 31 P NMR (81.01 MHz; DMSO reference to H3 PO4 ): d 91.4 (q of t, JPB 161.25 Hz, JPH unresolved); 11 B NMR (64.21 MHz; DMSO reference to BF3 áOEt2 ) d 40.58 (t of d, JBP 168.5 Hz, JBH 105.56 Hz); IR (KBr pellet) 2412, 2361 cm 1 m(BH); 2224 cm 1 m(CN). 2c: 1 H NMR (200 MHz, DMSO reference to TMS): d 1.2, 1.3 (d, 6H, CH3 ), 1.38, 1.39 (t, 6H, CH3 ), 1.0±1.3 (br, 2H, BH2 ), 2.39±2.4 (m, 2H, H-20 ), 3.12 (m, 1H, CH), 3.2 (s, 3H, OCH3 ), 3.91±4.21 (m, 2H, H-50 ), 4.06±4.13 (m, 1H, H-40 ), 4.22 (m, 4H, OCH2 ), 4.72±4.95 (m, 1H, H-30 ), 6.01 (br, s, NH), 6.53 (m, 1H, H-10 ), 8.01 (s, 1H, H-8), 8.21 (s, 1H, H-3); 13 C NMR (50.32 MHz; DMSO reference to TMS): d 14.1, 16.5 (CH3 ), 17.9 (CH2 ), 34.1 (CH attached to C@O), 59.2 (OCH2 ), 57.1, 56.5 (OCH), 51.7 (OCH3 ), 172.1 (C@O); 31 P NMR (81.01 MHz; DMSO reference to H3 PO4 ): d 90.8 (q of t, JPB 160.80 Hz, JPH unresolved); 11 B NMR (64.21 MHz; DMSO reference to BF3 áOEt2 ) d 41.28 (t of d, JBP 166.4 Hz, JBH 108.89 Hz); IR (KBr pellet) 2421, 2361 cm 1 m(BH); 2209 cm 1 m(CN). 2d: 1 H NMR (200 MHz, DMSO reference to TMS): d 1.37, 1.39 (t, 6H, CH3 ), 1.0±1.4 (br, 2H, BH2 ), 2.30±2.38 (m, 2H, H-20 ), 3.38 (s, 3H, OCH3 ), 3.72 (m, 2H, H-50 ), 3.91±4.11 (m, 1H, H-40 ), 4.24 (m, 4H, OCH2 ), 4.58±4.71 (m, 1H, H-30 ), 6.01 (d, 1H, H-5), 6.46 (m, 1H, H-10 ), 7.91 (d, 1H, H-6), 8.47 (m, 5H, Ar±H), 9.21 (br, s, NH); 13 C NMR (50.32 MHz, DMSO reference to BF3 áOEt2 ): d 14.6 (CH3 ), 16.7 (CH2 ), 61.4 (OCH2 ), 57.1, 57.1 (OCH), 52.8 (OCH3 ), 127.7 (C±Ar), 130.1, 128.7 (CH@CH), 168.9 (C@O); 31 P NMR (81.01 MHz; DMSO reference to H3 PO4 ): d 91.4 (q of t, JPB 161.89 Hz, JPH unresolved); 11 B NMR (64.21 MHz; DMSO reference to BF3 áOEt2 ) d 42.02 (t of d, JBP 167.4 Hz, JBH 110.32 Hz); IR (KBr pellet) 2398, 2349 cm 1 m(BH); 2219 cm 1 m(CN).
www.elsevier.com/locate/inoche
The ®rst substituted boranonucleic acids: a novel synthetic route Kamesh Vyakaranam a, Geeta Rana a, Bernard F. Spielvogel b, Narayan S. Hosmane a
a,*
Department of Chemistry and Biochemistry, The Michael Faraday Laboratories, Northern Illinois University, DeKalb, IL 60115-2862, USA b Metallo-Biotech International, Inc., 663 Teal Court, DeKalb, IL 60115-6201, USA Received 12 July 2001; accepted 31 July 2001
Abstract Diethylchlorophosphite-cyanoborane (1) was prepared in 65% yield by the reaction of sodium cyanoborohydride and bromine followed by re¯uxing with diethylchlorophosphite. Compound 1 was reacted further with several commercially available nucleosides to give substituted boranonucleic acids in 46±91% yields. Ó 2001 Elsevier Science B.V. All rights reserved. Keywords: Boranophosphate; Borane; Cyanoboranes; Nucleic acids; Derivatized boranes
There is increasing evidence that boron containing biomolecules can play a much greater role in the areas of life sciences such as pharmacology, medicine, biochemistry and nutrition than previously thought and, consequently, it has been shown in model studies that boron analogues of amino acids, nucleosides and nucleic acids have potent anti-cancer, anti-in¯ammatory, hypolipidemic, anti-osteoporotic, anti-viral, and other promising pharmacological activity [1]. Furthermore, important new diagnostic applications have been reported in the areas of PCR sequencing and DNA diagnostics using boronated DNA [2]. Substitution of a hydride with amine in the boranocarbonate structure would produce isoelectronic and isostructural analogues of the a-amino acids. Synthetic methodologies were developed and led to the ®rst boronated analog of glycine, H3 NBH2 C(O)OH with a pKa for the carboxylic proton of 8.3, some six log units higher than the analogous proton in glycine [3]. The incorporation of BH3 moiety in these species led to signi®cant problems in the chemical synthesis of boronated DNA in which highly reducing borane in¯uenced base-degradation. Consequently, base-degradation has been observed in all of the known boronated nucleosides except the one with the base, thymidine [4]. In addition, base-borane adducts of the nucleosides are generally quite toxic due to the presence of the borane * Corresponding author. Tel.: +1-815-753-3556; fax: +1-815-7534802. E-mail address: [email protected] (N.S. Hosmane).
moiety. Thus, borohydrides, boranocarbonates, and amine-boranes typically have LD50 values in the tens of mg/kg by intraperitoneal (IP) injection in mice. However, substitution of hydride, with ammonia as in the boron analog of glycine, H3 NBH2 COOH, produces a compound of very low toxicity, LD50 >2000 mg/kg [5]. In view of the above noted problems that are associated with the underivatized borane unit linked to the phosphorus in the phosphodiester backbone, we have embarked on an intensive eort in replacing the BH3 unit with much less toxic and less reducing moiety, such as derivatized boranes, BH2 X (X COOH, COOR, C(O)NHR, CN, etc.) [6]. Here we report hitherto unknown nucleosides incorporating derivatized borane moiety such as diethylchlorophosphite-cyanoborane (1), 50 -(diethylphosphite-cyanoborano)-30 , N6 -o-dibenzoyl20 -deoxyadenosine (2a), 50 -(diethylphosphite-cyanoborano)-30 -acetylthymidine (2b), 50 -(diethylphosphite0 2 cyanoborano)-3 -acetyl-N -isobutryl-20 -deoxyguanosine (2c), 50 (-diethylphosphite-cyanoborano)-30 , N4 -dibenzoyl-20 -deoxycytidine (2d), that are envisioned to exhibit properties ideal for use as new therapeutics. Diethylchlorophosphite-cyanoborane (1) was prepared in 65% yield by the reaction of sodium cyanoborohydride and bromine followed by re¯uxing with diethylchlorophosphite as a colorless oil (Scheme 1) that decomposed at 107 °C [7]. The proton-decoupled 11 B NMR spectra showed a doublet at d 42.18 ppm and the proton-decoupled 31 P NMR spectra showed a quartet at d 90.2 ppm that are consistent with the molecular geometry of 1. The IR spectra showed two
1387-7003/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 1 3 8 7 - 7 0 0 3 ( 0 1 ) 0 0 2 8 9 - 1
630
K. Vyakaranam et al. / Inorganic Chemistry Communications 4 (2001) 629±631
NaBH3CN
Br2 / DME
OEt
OEt EtO P Cl (BH2CN)X
P
EtO
DME
Cl
BH2CN 1 OEt
HO
P
EtO
1. 1
B
O
OR 2a 2b 2c 2d
NHBz
B=
N 2a = Ade
N H
R = Bz R = Ac R = Ac R = Bz NHBz
O
O N
N
B
O BH2CN
2. Et3N
OR
O
N
O
N
HN
NH
Buti-HN
2b = Thy
N
N H
2c = Gua
N N
O
2d = Cyt
Scheme 1.
singlets, at 2470 and 2395 cm 1 due to BH stretches and the one at 2192 cm 1 was assigned to a C±N bond. This compound was hydrolytically stable for few days but slowly decomposed to dimethylphosphate over a period of days. The borano-phosphate nucleosides (2(a±d)) were prepared by the reaction of 1 with suitable 30 protected nucleosides according to Scheme 1 [8]. The reactions were carried out in anhydrous THF at room temperature using one equivalent of triethyl amine that was used to quench the hydrogen chloride produced during the reaction. The nucleosides were obtained as colorless oils by puri®cation using ¯ash chromatography on silica gel with a solvent mixture of ethyl acetate:hexane (9:1). The yields obtained were 91%, 47%, 46% and 88%, for the deoxy-adenosine, deoxy-thymidine, deoxyguanosine and deoxy-cytidine derivatives, respectively. The yields for the deoxy-thymidine and deoxy-guanosine derivatives were less and were expected due to degradation of the compounds during the puri®cation process. All compounds were characterized by IR spectra, 1 H, 11 B and 13 C NMR spectra and elemental analysis. The most important information, that were found in the spectra, are worthy of further comments; for example, the proton-decoupled 31 P NMR spectra of (2(a±d)) showed a quartet corresponding to a cyanoborane phosphate group in each molecule [9]. The protondecoupled 11 B NMR spectrum of each corresponding species contained a doublet due to the cyanoborane phosphate group [9]. The IR spectra of each compound showed two singlets; one for the BH unit and another as a broad singlet for a CN moiety. The formulations of compounds (2(a±d)) are further supported by their mi-
croanalytical data [8]. The 13 C NMR spectra of 1 and (2(a±d)) showed no surprises and, therefore, deserve no special comments. This work presents the ®rst report on a novel phosphitylating agent and a set of boronated nucleosides. Nevertheless, further exploration of these species in the nucleic acid backbone modi®cation is therefore warranted in order to greatly increase the scope and application of this novel class of nucleic acids. The pharmacological properties and further chemistry of these compounds are currently underway in our laboratories. Acknowledgements This work was supported by grants from the National Science Foundation (CHE-9988045), the donors of the Petroleum Research Fund, administered by the American Chemical Society, and Northern Illinois University through Presidential Research Professorship (to NSH). References [1] [a] A. Hasan, H. Li, J. Tomasz, B.R. Shaw, Nucl. Acid Res. 24 (1996) 2150±2157; [b] H. Li, K. Porter, F. Huang, B.R. Shaw, Nucl. Acid Res. 23 (1995) 4495±4501; [c] A. Sood, B.R. Shaw, B.F. Spielvogel, J. Am. Chem. Soc. 112 (1990) 9000±9001; [d] A. Sood, B.F. Spielvogel, B.R. Shaw, J. Am. Chem. Soc. 111 (1989) 9234±9235;
K. Vyakaranam et al. / Inorganic Chemistry Communications 4 (2001) 629±631
[2] [3] [4]
[5] [6]
[7]
[8]
[e] B.F. Spielvogel, A. Sood, J. Tomasz, B.R. Shaw, S. Karthikeyan, Neutron Capture Ther. (1993) 361±365; [f] I.H. Hall, E.S. Hall, L. Chi, B.R. Shaw, A. Sood, B.F. Spielvogel, Anticancer Res. 12 (1992) 1091±1098; [g] A. Sood, B.R. Shaw, B.F. Spielvogel, E.S. Hall, L.K. Chi, I.H. Hall, Pharmazie 47 (1992) 833±838; [h] J. Tomasz, B.R. Shaw, K.W. Porter, B.F. Spielvogel, A. Sood, Angew. Chem. Int. Ed., Engl. 31 (1992) 1373±1375. K.W. Porter, J.D. Briley, B.R. Shaw, Nucl. Acid Res. 25 (1997) 1611±1617. K.H. Scheller, B.R. Martin, B.F. Spielvogel, A.T. McPhail, Inorg. Chim. Acta 57 (1982) 227. [a] B.F. Spielvogel, A. Sood, B.R. Shaw, I.H. Hall, R.G. Fairchild, B.H. Laster, C. Gordon, Prog. Neutron Capture Ther. Cancer (1992) 211±213; [b] A.P. Higson, A. Sierzchala, H. Brummel, Z. Zhao, M.H. Caruthers, Tetrahedron Lett. 39 (1998) 3899±3902. B.F. Spielvogel, M.K. Das, A.T. McPhail, K.D. Onan, I.H. Hall, J. Am. Chem. Soc. 102 (1980) 6343±6344. [a] A.T. McPhail, K.D. Onan, B.F. Spielvogel, P. Wisian-Neilson, J. Chem. Res. (1978) 205; [b] P. Wisian-Neilson, M.K. Das, B.F. Spielvogel, Inorg. Chem. 17 (1978) 2327±2329; [c] B.F. Spielvogel, F. Harchelroad, P. Wisian-Neilson, J. Inorg. Nucl. Chem. 41 (1979) 1223±1227. Bromine (6.24 g, 39.9 mmol) was added drop-wise with stirring to a solution of sodium cyanoborohydride (5 g, 79.0 mmol) in anhydrous dimethoxy ethane (80 ml). The ®ltrate was mixed with diethylchlorophosphite (12.52 g, 80 mmol) under nitrogen and heated at re¯ux for 2 days. After ®ltration the solvent was removed under reduced pressure to give an oil. The oil was dissolved in ether (50 ml), washed with pentane (3´50 ml) and the solvent was removed under reduced pressure to give diethylchlorophosphitecyanoborane (1) as colorless oil in 65% yield 1 H NMR (200 MHz, DMSO reference to TMS): d 1.34 (t, 6H, CH3 ), 4.22 (m, 4H, CH2 ); 13 C NMR (50.32 MHz; DMSO reference to TMS): d 17.5 (CH3 ), 63.7 (OCH2 ); 31 P NMR (81.01 MHz; DMSO reference to H3 PO4 ): d 90.2 (q of t, JPB 141.80 Hz, JPH unresolved); 11 B NMR (64.21 MHz; DMSO reference to BF3 áOEt2 ) d 42.18 (t of d, JBP 139.6 Hz, JBH 99.52 Hz); IR (KBr pellet) 2470, 2395 cm 1 m(BH); 2192 cm 1 m(CN); Anal. calcd for C5 H12 O2 NBPCl: C, 30.42; H, 6.09; N, 7.09. Found: C, 31.01; H, 5.99; N, 6.98. N6 , 30 -o-Dibenzoyl-20 -deoxyadenosine (10.0 mg, 0.06 mmol), 30 acetylthymidine (0.35 g, 1.24 mmol), N2 -isobutryl-30 -acetyl-20 deoxyguanosine (50.0 mg, 0.13 mmol), or N4 , 30 -o-dibenzoyl-20 deoxycytidine (25.0 mg, 0.06 mmol), respectively, diethylchlorophosphite-cyanoborane (12.0 mg, 0.06 mmol), (0.24 g, 1.24 mmol), (26.0 mg, 0.13 mmol) and (12.0 mg, 0.06 mmol), respectively and triethylamine (6.0 mg, 0.06 mmol), (0.5 mg, excess), (13.3 mg, 0.13 mmol), (6.0 mg, 0.06 mmol), respectively, were dissolved in anhydrous THF and the mixture was stirred at room temperature for 6 h. After ®ltration to remove insoluble materials, the solvent was removed under reduced pressure. The residue was taken up in dichloromethane (20 ml) and was washed with water (5´15 ml). The organic layer was dried, ®ltered and concentrated under reduced pressure. The residue was puri®ed by ¯ash chromatography on silica gel using ethyl acetate: hexane (9:1) to give 50 -(diethylphosphite-cyanoborano)-30 , N6 -o-dibenzoyl-20 deoxyadenosine (2a, 31 mg, 90.7%, anal. calcd. for C29 H32 O7 N6 BP: C, 56.09; H, 5.16; N, 13.54. Found: C, 55.89; H, 5.09;
631
N, 13.01), 50 -(diethylphosphite-cyanoborano)-30 -acetylthymidine (2b, 260 mg, 46.5%, anal. calcd. for C17 H27 O8 N3 BP: C, 45.82; H, 6.06; N, 9.43. Found: C, 45.74; H, 5.98; N, 9.01), 50 -(diethylphosphite-cyanoborano)-30 -acetyl-N2 -isobutryl-20 -deoxyguanosine (2c, 35 mg, 45.8%, anal. calcd. for C21 H32 O8 N6 BP: C, 46.64; H, 5.92; N, 15.55. Found: C, 46.02; H, 5.81; N, 15.12) and 50 (diethylphosphite-cyanoborano)-30 , N4 -dibenzoyl-20 -deoxycytidine (2d, 28 mg, 87.7%, anal. calcd. for C28 H32 O8 N4 BP: C, 56.35; H, 5.37; N, 9.39. Found: C, 55.99; H, 5.24; N, 10.01) as colorless oil, respectively. [9] The spectroscopic data for 2a: 1 H NMR (200 MHz, DMSO reference to TMS): d 1.39, 1.40 (t, 6H, CH3 ), 1.0±1.6 (br, 2H, BH2 ), 2.41±2.6 (m, 2H, H-20 ), 3.2 (s, 3H, OCH3 ), 3.91±4.12 (m, 2H, H-50 ), 4.12±4.14 (m, 1H, H-40 ), 4.26 (m, 4H, OCH2 ), 4.81±5.0 (m, 1H, H30 ), 6.46 (m, 1H, H-10 ), 8.11 (s, 1H, H-8), 8.35 (s, 1H, H-2), 8.62 (m, 5H, Ar±H), 9.01 (br, s, NH); 13 C NMR (50.32 MHz; DMSO reference to TMS): d 14.4 (CH3 ), 17.3 (CH2 ), 60.4 (OCH2 ), 58.1, 56.3 (OCH), 53 (OCH3 ), 129 (C±Ar), 170.7 (C@O); 31 P NMR (81.01 MHz; DMSO reference to H3 PO4 ): d 89.7 (q of t, JPB 161.20 Hz, JPH unresolved); 11 B NMR (64.21 MHz; DMSO reference to BF3 áOEt2 ) d 41.8 (t of d, JBP 169.4 Hz, JBH 111.95 Hz); IR (KBr pellet) 2408, 2359 cm 1 m(BH); 2200 cm 1 m(CN). 2b: 1 H NMR (200 MHz, DMSO reference to TMS): d 1.41, 1.44 (t, 6H, CH3 ), 1.0±1.8 (br, 2H, BH2 ), 1.95 (s, 3H, CH3 ), 2.30±2.41 (m, 2H, H-20 ), 3.2 (s, 3H, OCH3 ), 4.18±4.24 (m, 2H, H50 ), 4.13±4.15 (m, 1H, H-40 ), 4.28 (m, 4H, OCH2 ), 5.26 (m, 1H, H30 ), 6.41 (m, 1H, H-10 ), 6.71 (s, 1H, H-3), 7.36 (d, 1H, H-6), 9.21 (br, s, NH); 13 C NMR (50.32 MHz; DMSO reference to TMS): d 14.2 (CH3 ), 18.4 (CH2 ), 60.9 (OCH2 ), 57.9, 56.1 (OCH), 52.8 (OCH3 ), 169.7 (C@O); 31 P NMR (81.01 MHz; DMSO reference to H3 PO4 ): d 91.4 (q of t, JPB 161.25 Hz, JPH unresolved); 11 B NMR (64.21 MHz; DMSO reference to BF3 áOEt2 ) d 40.58 (t of d, JBP 168.5 Hz, JBH 105.56 Hz); IR (KBr pellet) 2412, 2361 cm 1 m(BH); 2224 cm 1 m(CN). 2c: 1 H NMR (200 MHz, DMSO reference to TMS): d 1.2, 1.3 (d, 6H, CH3 ), 1.38, 1.39 (t, 6H, CH3 ), 1.0±1.3 (br, 2H, BH2 ), 2.39±2.4 (m, 2H, H-20 ), 3.12 (m, 1H, CH), 3.2 (s, 3H, OCH3 ), 3.91±4.21 (m, 2H, H-50 ), 4.06±4.13 (m, 1H, H-40 ), 4.22 (m, 4H, OCH2 ), 4.72±4.95 (m, 1H, H-30 ), 6.01 (br, s, NH), 6.53 (m, 1H, H-10 ), 8.01 (s, 1H, H-8), 8.21 (s, 1H, H-3); 13 C NMR (50.32 MHz; DMSO reference to TMS): d 14.1, 16.5 (CH3 ), 17.9 (CH2 ), 34.1 (CH attached to C@O), 59.2 (OCH2 ), 57.1, 56.5 (OCH), 51.7 (OCH3 ), 172.1 (C@O); 31 P NMR (81.01 MHz; DMSO reference to H3 PO4 ): d 90.8 (q of t, JPB 160.80 Hz, JPH unresolved); 11 B NMR (64.21 MHz; DMSO reference to BF3 áOEt2 ) d 41.28 (t of d, JBP 166.4 Hz, JBH 108.89 Hz); IR (KBr pellet) 2421, 2361 cm 1 m(BH); 2209 cm 1 m(CN). 2d: 1 H NMR (200 MHz, DMSO reference to TMS): d 1.37, 1.39 (t, 6H, CH3 ), 1.0±1.4 (br, 2H, BH2 ), 2.30±2.38 (m, 2H, H-20 ), 3.38 (s, 3H, OCH3 ), 3.72 (m, 2H, H-50 ), 3.91±4.11 (m, 1H, H-40 ), 4.24 (m, 4H, OCH2 ), 4.58±4.71 (m, 1H, H-30 ), 6.01 (d, 1H, H-5), 6.46 (m, 1H, H-10 ), 7.91 (d, 1H, H-6), 8.47 (m, 5H, Ar±H), 9.21 (br, s, NH); 13 C NMR (50.32 MHz, DMSO reference to BF3 áOEt2 ): d 14.6 (CH3 ), 16.7 (CH2 ), 61.4 (OCH2 ), 57.1, 57.1 (OCH), 52.8 (OCH3 ), 127.7 (C±Ar), 130.1, 128.7 (CH@CH), 168.9 (C@O); 31 P NMR (81.01 MHz; DMSO reference to H3 PO4 ): d 91.4 (q of t, JPB 161.89 Hz, JPH unresolved); 11 B NMR (64.21 MHz; DMSO reference to BF3 áOEt2 ) d 42.02 (t of d, JBP 167.4 Hz, JBH 110.32 Hz); IR (KBr pellet) 2398, 2349 cm 1 m(BH); 2219 cm 1 m(CN).