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Synlett 2007(2): 0239-0242  
DOI: 10.1055/s-2007-968002
LETTER
© Georg Thieme Verlag Stuttgart · New York

Synthesis of Sugar-Lysine Chimera with Integrated gluco-Configured 1,3-Hydroxyamine Motif

Kaidong Zhang, Jialiang Wang, Zhizhi Sun, Dung-Huang Nguyen, Frank Schweizer*
Department of Chemistry, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada
Fax: +1(204)4747608; e-Mail: schweize@cc.umanitoba.ca;
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Publikationsverlauf

Received 4 July 2006
Publikationsdatum:
24. Januar 2007 (online)

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Abstract

The paper describes the synthesis of glucose-configured sugar-lysine chimeras in which the side chain of lysine is conformationally constrained via incorporation into a d-glucose scaffold. Key step in the synthesis is a high-yielding, reductive ring opening of an exocyclic glucose-derived epoxide to form an α-hydroxyester that can be converted into chimeric sugar-lysine analogues. To demonstrate the use of these novel chimeric sugar-lysine building blocks in peptide coupling, we replaced d-lysine in the antimicro­bial dipeptide sequence kW by a d-glucose-d-lysine chimera.

Key words

sugar-lysine chimera - reductive ring opening - epoxides

16

Synthetic Procedures for Compounds 12-17.
Synthesis of Compounds 12-15.
Ester 11 (60 mg, 0.16 mmol) was treated with LiOH (7 mg, 0.31 mmol) for 8 h at r.t. in aq THF (1:1), and then acidified with formic acid (100 µL). The solution was extracted with EtOAc (6 × 10 mL) and the combined organic layer solvent was dried (Na2SO4) and concentrated to afford inseparable mixture of crude acids 12 and 13 (59 mg, quant.), which was treated with Cs2CO3 (61 mg, 0.18 mmol) and MeI (30 µL, 0.48 mmol) in DMF. The reaction was worked up with H2O and extracted with EtOAc (4 × 15 mL); the combined organic phases were dried (Na2SO4) and concentrated. The crude was acetylated by dissolving it in a 1:1 mixture containing Ac2O (0.5 mL) and pyridine (0.5 mL). The crude mixture was purified by the flash chromatography (EtOAc-hexane, 1:2) to afford compound 14 (61 mg, 80%) and 15 (15 mg, 20%). Compound 14 was identical to the product obtained by acetylation of compound 11.
Synthesis of Compound 16.
Acid 12 (46 mg, 0.12 mmol) was dissolved in MeOH (4 mL) and hydrogentated for 20 min using 20 wt% Pd/C. The solution was filtered and the solvent was evaporated in vacuo. The solid residue was dissolved in aq acetone (3 mL, 1:1) and treated with 9-fluorenylmethyl pentafluorophenyl carbonate (91 mg, 0.24 mmol) and NaHCO3 (31 mg, 0.37 mmol) for 4 h at r.t. Then, H2O (10 mL) was added and the aqueous layer was extracted with EtOAc (6 × 10 mL). Finally, the solvent was dried (Na2SO4) and concentrated. The crude product was purified by flash column chromatography (MeOH-EtOAc, 1:1) to afford compound 16 (45 mg, 63%).
Synthesis of Compound 17. To the mixture of Fmoc-Trp(Boc)-OH (205 mg, 0.39 mmol) and benzylamine (165 µL, 1.51 mmol) in DMF (5 mL) was added TBTU (249 mg, 0.77 mmol) and DIPEA (340 µL, 1.95 mmol). The reaction was stirred for 2 h at r.t. The solvent was removed in vacuo and the residue was purified by flash column silica gel chromatography (2:1, hexane-EtOAc) to yield the Fmoc-Trp(Boc)-NHBn (151 mg, 63%). The solution of Fmoc-Trp(Boc)-NHBn (151 mg, 0.25 mmol) and piperidine (0.5 mL) in DMF (2 mL) was stirred for 1 h at r.t. The solvent was removed in vacuo and the crude product was purified by flash column silica gel chromatography (from EtOAc to 5% MeOH in EtOAc) to afford the NH2-Trp(Boc)-NHBn (81 mg, 80%). Compound 16 (23 mg, 0.04 mmol) was dissolved in DMF (2 mL) and NH2-Trp(Boc)-NHBn (72 mg, 0.18 mmol), TBTU (33 mg, 0.10 mmol), and DIPEA (37 µL, 0.21 mmol). The mixture was stirred for 4 h at r.t. before removing the solvent under reduced pressure. The crude product was purified by flash chromatography using EtOAc as eluent to afford 17 (24 mg, 63%).
Characteristic Spectroscopic Data for Compounds 14-17. Compound 14: 1H NMR (300 MHz, CDCl3, r.t., TMS): δ = 1.45 (s, 9 H), 2.00 (s, 3 H), 2.02 (s, 3 H), 2.05 (s, 3 H), 3.20-3.33 (m, 2 H), 3.64-3.70 (m, 1 H, H-7), 3.77 (s, 3 H), 3.87 (dd, 1 H, H-3, J = 9.9, 1.7 Hz), 4.66 (dd, 1 H, H-2, J = 9.2, 1.7 Hz), 5.02 (dd, 1 H, H-6, J = 9.3, 9.7 Hz), 5.16 (dd, 1 H, H-5, J = 9.3, 9.1 Hz), 5.25 (dd, 1 H, H-4, J = 9.9, 9.1 Hz), 5.46 (d, 1 H, N-H, J = 9.2 Hz). 13C NMR (100 MHz, CDCl3, r.t.): δ = 20.57, 20.58, 20.66, 28.27 (3 C), 50.83, 52.73, 53.47, 68.77, 69.03, 74.21, 77.77, 78.76, 80.46, 168.78, 168.80, 169.39, 169.51, 170.29. MS (ES): m/z calcd for C20H30N4NaO11 [M + Na]+: 525.18; found: 525.32. Anal. Calcd (%) for C20H30N4O11: C, 47.81; H, 6.02; N, 11.15. Found: C, 48.08; H, 6.15; N, 10.77.
Compound 15: 1H NMR (300 MHz, CDCl3, r.t., TMS): δ = 1.44 (s, 9 H), 1.98 (s, 3 H), 2.03 (s, 3 H), 2.04 (s, 3 H), 3.13-3.29 (m, 2 H, H-8a, H-8b), 3.64-3.71 (m, 1 H, H-7), 3.78 (s, 3 H), 4.16 (dd, 1 H, H-3, J = 9.9, 2.3 Hz), 4.70 (dd, 1 H, H-2, J = 10.5, 2.3 Hz), 5.00 (dd, 1 H, H-6, J = 9.5, 9.5 Hz), 5.06 (dd, 1 H, H-4, J = 9.9, 9.5 Hz), 5.20 (dd, 1 H, H-5, J = 9.5, 9.5 Hz), 5.13 (d, 1 H, N-H, J = 10.5 Hz). 13C NMR (100 MHz, CDCl3, r.t.): δ = 21.23, 21.34 (2 C), 28.88 (3 C), 51.30, 53.02, 53.46, 68.12, 69.84, 74.59, 78.04, 78.47, 79.82, 167.63, 168.12, 168.84, 169.37, 169.72. MS (ES): m/z calcd for C20H30N4NaO11 [M + Na]+: 525.18; found: 525.27. Anal. Calcd (%) for C20H30N4O11: C, 47.81; H, 6.02; N, 11.15. Found: C, 47.98; H, 6.25; N, 11.55.
Compound 16: 1H NMR (300 MHz, CD3OD, r.t., TMS): δ = 1.43 (s, 9 H), 2.98-3.13 (m, 2 H, H-6 and H-8a), 3.18 (m, 1 H, H-7), 3.22-3.44 (m, 2 H, H-3, H-5), 3.62-3.80 (m, 2 H, H-4, H-8b), 4.23 (t, 1 H, J = 6.8 Hz), 4.32-4.48 (m, 3 H), 7.28-7.87 (m, 8 H). 13C NMR (100 MHz, CDCl3, r.t.): δ = 28.88, 43.42, 48.54, 56.37, 67.78, 72.04, 73.14, 79.03, 80.38, 80.76, 82.97, 120.94-128.78 (arom. C), 142.61-145.43 (arom. C), 157.71, 159.12, 169.46. MS (ES): m/z calcd for C28H33N2O10 [M - H]-: 557.21; found: 557.09.
Compound 17: 1H NMR (300 MHz, CDCl3, r.t., TMS): δ = 1.38 (s, 9 H), 1.63 (s, 9 H), 3.04-3.34 (m, 6 H), 3.37-3.61 (m, 5 H), 3.71-3.83 (m, 1 H), 4.03-4.37 (m, 5 H), 4.45 (dd, 1 H, J = 6.7, 2.2 Hz), 4.75-4.85 (m, 1 H), 5.45-5.56 (br s, 1 H, NH), 6.12-6.29 (br s, 1 H, NH), 6.29-6.46 (br s, 1 H, NH), 6.73-6.91 (m, 2 H), 6.96-7.03 (br, 1 H, NH), 7.08-8.18 (m, 16 H). HRMS (ES): m/z calcd for C51H59N5NaO12 [M + Na]+: 956.40524; found: 956.40537.