Synthesis of Anomeric Sulfur Analogues of CMP-Neu5Ac Containing Tethered Alkane or Arene

Abstract

A new approach to the synthesis of anomeric sulfur analogues of CMP-Neu5Ac containing alkane or arene linkage 1a-d is described. The procedure involves the high β-stereoselectivity in sialylation of the peracetylated sialic acid methyl ester 4 with mercaptoalkyl (aryl) trichloroacetate 5a-d, followed by selective deprotection of the trichloroacetyl group to the corresponding hydroxyalkyl and hydroxyaryl thioglycosides 2a-d. Subsequent O-phosphitylation of 2a-d with respective 3a or 3c, followed by oxidation and deprotection led to the isolation of the target compounds 1a-d in good yields.

sialylation - hydroxyalkyl (aryl) thioglycosides - selective deprotection - sialyltransferase

References

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For example, treatment of 4 and 2-mercaptoethyl trimethylsilyl ether (or 2-mercaptoethyl tert-butyldiphenylsilyl ether) with boron trifluoride in dichloromethane gave the desired thioglycoside in low yield, along with the formation of large amounts of bis-(2-trimethylsilyloxyethyl) disulfide or bis-(2-tert-butyldiphenylsilyloxyethyl) disulfide. Condensation of the 2-chlorosialic acid with the 2-mercaptoethyl benzoate gave the thioglycoside in low yield. The products were contaminated with the sialic acid 2,3-elimination product, see:

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9

The required compounds 5a-d were prepared from corresponding mercaptoalkyl(aryl) alcohols, respectively, by treating them with trichloroacetyl chloride in dichloromethane at 0 °C for 4 h.

The configuration of 6a-d was determined by measuring the chemical shifts of H_3eq and H₄. The formation of β-anomer 6a caused an upfield shift of H_3eq to δ = 2.52 ppm while the chemical shift of H_3eq of α-anomer 6a remained δ = 2.72 ppm. In addition, H₄ is shifted in the other direction. Thus H₄ in the β-anomer 6a occurs at δ = 5.41 ppm in contrast to the chemical shift of α-anomer at δ = 4.84 ppm. Several reports demonstrated that H_3eq of a β-linked alkyl thioglycoside of sialic acid diplayed a signal upfield relative to that of the corresponding α-anomer, see:

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12

CMP-Neu5Ac mimetics that contain a spiro-ring.

13

Selected physical data. Compound 2a: TLC (100% EtOAc): R_f = 0.40. ¹H NMR (500 MHz, CDCl₃): δ = 5.89 (d, J = 9.3 Hz, 1 H), 5.44 (s, 1 H), 5.26 (td, J = 4.5, 11.0 Hz, 1 H), 5.21(m, 1 H), 4.96 (dd, J = 2.1, 12.2 Hz, 1 H), 4.42 (d, J = 10.4 Hz, 1 H), 4.05 (m, 2 H), 3.77 (s, 3 H), 3.75 (m, 1 H), 3.62 (m, 1 H), 2.84 (m, 1 H), 2.76 (m, 1 H), 2.58 (br s, 1 H), 2.50 (dd, J = 4.7, 13.8 Hz, 1 H), 2.12 (m, 1 H), 2.10 (s, 3 H), 2.05 (s, 3 H), 2.00 (s, 3 H), 1.98 (s, 3 H), 1.84 (s, 3 H). ¹³C NMR (125 MHz, CDCl₃): δ = 171.44, 170.89, 170.85, 170.36, 170.16, 168.47, 84.43, 72.73, 72.19, 69.33, 68.81, 62.52, 60.92, 52.90, 48.96, 36.97, 31.13, 22.99, 20.93, 20.85, 20.75, 20.65. HRMS-FAB: calcd for C₂₂H₃₄NO₁₃S (M + H)⁺: 552.1951. Found: 552.1961. Compound 2b: TLC (100% EtOAc): R_f = 0.40. ¹H NMR (400 MHz, CDCl₃): δ = 5.85 (d, J = 10.2 Hz, 1 H), 5.44 (t, J = 2.3 Hz, 1 H), 2.59 (m, 1 H), 5.23 (m, 1 H), 4.96 (dd, J = 2.5, 12.3 Hz, 1 H), 4.36 (dd, J = 2.3, 10.4 Hz, 1 H), 4.08 (m, 2 H), 3.80 (s, 3 H), 3.67 (m, 2 H), 2.72 (m,2 H), 2.51 (dd, J = 4.9, 13.8 Hz, 1 H), 2.46 (br s, 1 H), 2.17 (m, 1 H), 2.13 (s, 3 H), 2.06 (s, 3 H), 2.02 (s, 3 H), 2.01 (s, 3 H), 1.86 (s, 3 H), 1.77 (m, 2 H). ¹³C NMR (100 MHz, CDCl₃): δ = 171.24, 170.98, 170.86, 170.36, 170.12, 168.35, 84.70, 72.67, 62.22, 69.31, 68.74, 62.52, 60.77, 52.84, 49.10, 37.04, 31.75, 24.83, 22.92, 20.91, 20.79, 20.72, 20.64. HRMS-FAB: calcd for C₂₃H₃₆NO₁₃S (M + H)⁺: 556.1907. Found: 556.1911. Anal. Calcd for C₂₃H₃₅NO₁₃S: C, 48.84; H, 6.24; N, 2.48; S, 5.67. Found: C, 48.59; H, 7.02; N, 2.37; S, 5.61. Compound 2c: TLC (100% EtOAc): R_f = 0.40. ¹H NMR (400 MHz, CDCl₃): δ = 7.40 (d, J = 8.2 Hz, 2 H), 7.32 (d, J = 8.2 Hz, 2 H), 5.79 (d, J = 10.2 Hz, 1 H), 5.42 (t, J = 2.5 Hz, 1 H), 5.39 (m, 1 H), 4.79 (td, J = 2.2, 8.5 Hz, 1 H), 4.66 (s, 2 H), 4.53 (dd, J = 2.5, 5.5 Hz, 1 H), 4.49 (dd, J = 2.4, 7.2 Hz, 1 H), 4.09 (m, 1 H), 4.01 (m, 1 H), 3.63 (s, 3 H), 2.63 (dd, J = 4.8, 13.9 Hz, 1 H), 2.52 (br s, 1 H), 2.10 (dd, J = 11.7, 13.9 Hz, 1 H), 2.08 (s, 3 H), 2.04 (s, 3 H), 2.03 (s, 3 H), 1.98 (s, 3 H), 1.87 (s, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 171.10, 170.92, 170.34, 170.10, 168.31, 143.06, 135.86, 127.60, 127.51, 88.28, 73.09, 72.80, 69.04, 68.81, 64.40, 62.56, 52.67, 49.27, 37.34, 23.05, 20.99, 20.82, 20.66. HRMS-FAB: calcd for C₂₇H₃₆NO₁₃S (M + H)⁺: 614.1907. Found: 614.1910. Compound 2d: TLC (100% EtOAc): R_f = 0.50. ¹H NMR (400 MHz, CDCl₃): δ = 7.53 (m, 1 H), 7.36 (m, 2 H), 7.20 (m, 1 H), 5.93 (d, J = 10.2 Hz, 1 H), 5.41 (m, 2 H), 4.90 (d, J = 12.9 Hz, 1 H), 4.78 (d, J = 12.9 Hz, 1 H), 4.71 (td, J = 2.2, 8.3 Hz, 1 H), 4.67 (dd, J = 2.5, 10.5 Hz, 1 H), 4.58 (dd, J = 2.2, 12.3 Hz, 1 H), 4.09 (m, 2 H), 3.56 (s, 3 H), 2.73 (dd, J = 4.7, 13.8 Hz, 1 H), 2.63 (br s, 1 H), 2.15 (dd, J = 11.6, 13.8 Hz, 1 H), 2.11 (s, 3 H), 2.05 (s, 3 H), 2.04 (s, 3 H), 2.02 (s, 3 H), 1.86 (s, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 171.36, 171.00, 170.36, 170.25, 170.17, 168.49, 144.64, 136.84, 129.79, 129.25, 127.88, 89.29, 73.24, 73.13, 69.11, 68.76, 62.79, 62.54, 52.74, 48.92, 38.13, 22.93, 20.97, 20.80, 20.72, 20.62. HRMS-FAB: calcd for C₂₇H₃₆NO₁₃S (M + H)⁺: 614.1907. Found: 614.1913. Compound 1a: ¹H NMR (400 MHz, D₂O): δ = 8.21 (d, J = 7.6 Hz, 1 H), 6.34 (d, J = 7.6 Hz, 1 H), 5.98 (d, J = 7.6 Hz, 1 H), 4.40-4.35 (m, 3 H), 4.28 (m, 1 H), 4.22 (d, J = 7.6 Hz, 1 H), 4.15 (m, 2 H), 4.04 (m, 2 H), 3.91-3.84 (m, 3 H), 3.70 (dd, J = 7.6 Hz, 1 H), 3.62 (d, J = 7.6 Hz, 1 H), 2.88 (m, 2 H), 2.54 (dd, J = 7.6 Hz, 1 H), 2.09 (s, 3 H), 2.06 (m, 1 H). ¹³C NMR (100 MHz, D₂O): δ = 175.01, 173.43, 159.28, 148.55, 144.24, 95.34, 89.94, 85.17, 83.37 (d, J = 8.7 Hz), 74.40, 71.19, 69.99, 69.28, 68.12, 67.42, 64.87 (d, J = 4.0 Hz), 64.16 (d, J = 4.7 Hz), 63.50, 52.27, 39.59, 28.82 (d, J = 7.4 Hz), 22.25. ³¹P NMR (D₂O, H₃PO₄ reference): δ = 0.12. HRMS-MALDI: calcd for C₂₂H₃₅N₄O₁₆PSNa (M + 2 H + Na)⁺: 697.1403. Found: 697.1387. Compound 1b: ¹H NMR (400 MHz, D₂O): δ = 8.00 (d, J = 7.6 Hz, 1 H), 6.17 (d, J = 7.6 Hz, 1 H), 6.03 (d, J = 4.0 Hz, 1 H), 4.37 (m, 2 H), 4.31 (m, 1 H), 4.22 (m, 1 H), 4.16 (d, J = 10.5 Hz, 1 H), 4.12 (m, 1 H), 4.03 (m, 1 H), 4.00-3.84 (m, 5 H), 3.70 (m, 1 H), 3.57 (d, J = 9.0 Hz, 1 H), 2.62 (m, 2 H), 2.50 (dd, J = 4.8, 13.6 Hz, 1 H), 2.10 (s, 3 H), 1.90 (m, 3 H). ¹³C NMR (100 MHz, D₂O): δ = 176.46, 174.89, 165.72, 157.06, 141.69, 96.55, 89.49, 87.54, 82.86 (d, J = 8.7 Hz), 74.37, 71.08, 70.18, 69.42, 68.46, 67.96, 65.08 (d, J = 5.5 Hz), 64.25 (d, J = 4.8 Hz), 63.52, 52.45, 40.98, 29.47 (d, J = 7.2 Hz), 24.63, 22.26. ³¹P NMR (D₂O, H₃PO₄ reference): δ = 0.36. HRMS-MALDI: calcd for C₂₃H₃₇N₄O₁₆PSNa (M + 2 H + Na)⁺: 711.1559. Found: 711.1566. Compound 1c: ¹H NMR (400 MHz, D₂O): δ = 8.02 (d, J = 7.9 Hz, 1 H), 7.56 (d, J = 8.1 Hz, 2 H), 7.43 (d, J = 8.1 Hz, 2 H), 6.10 (d, J = 7.9 Hz, 1 H), 5.88 (d, J = 3.7 Hz, 1 H), 4.96 (d, J = 8.1 Hz, 2 H), 4.50 (d, J = 10.4 Hz, 1 H), 4.30-4.17 (m, 5 H), 4.03 (m, 1 H), 3.95 (t, J = 10.2 Hz, 1 H), 3.84-3.77 (m, 2 H), 3.69-3.63 (m, 2 H), 2.72 (dd, J = 4.7, 13.7 Hz, 1 H), 2.12 (m, 1 H), 2.11 (s, 3 H). ¹³C NMR (100 MHz, D₂O): δ = 174.97, 171.92, 158.97, 148.26, 144.00, 139.14 (d, J = 6.3 Hz), 135.39, 12911, 128.26, 95.04, 89.95, 89.91, 83.17 (d, J = 8.2 Hz), 74.24, 71.75, 70.20, 68.09, 68.53, 67.22 (d, J = 4.5 Hz), 66.95, 64.17 (d, J = 4.1 Hz), 63.18, 52.34, 39.95, 22.27. ³¹P NMR (D₂O, H₃PO₄ reference): δ = 0.15. HRMS-MALDI: calcd for C₂₇H₃₇N₄O₁₆PSNa (M + 2 H + Na)⁺: 759.1559. Found: 759.1567. Compound 1d: ¹H NMR (400 MHz, D₂O): δ = 7.94 (d, J = 7.7 Hz, 1 H), 7.63 (m, 1 H), 7.50 (m, 1 H), 7.34 (m, 2 H), 6.00 (d, J = 7.7 Hz, 1 H), 5.92 (d, J = 3.7 Hz, 1 H), 5.19 (m, 1 H), 5.05 (m, 1 H), 4.28-4.19 (m, 6 H), 4.07 (m, 1 H), 3.94 (t, J = 10.2 Hz, 1 H), 3.77 (dd, J = 1.7, 11.4 Hz, 1 H), 3.66-3.60 (m, 2 H), 3.53 (d, J = 8.9 Hz, 1 H), 2.68 (dd, J = 4.6, 13.7 Hz, 1 H), 2.10 (s, 3 H), 1.97 (m, 1 H). ¹³C NMR (100 MHz, D₂O): δ = 175.39, 174.91, 163.51, 154.25, 142.26, 138.00 (d, J = 6.9 Hz), 132.58, 132.06, 129.41, 128.89, 127.92, 95.98, 91.09, 89.80, 82.99 (d, J = 8.6 Hz), 74.47, 72.08, 70.31, 69.20, 68.64, 67.69, 66.50 (d, J = 4.7 Hz), 64.02 (d, J = 4.5 Hz), 63.27, 52.38, 41.67, 22.29. ³¹P NMR (D₂O, H₃PO₄ reference): δ = 0.17. HRMS-MALDI: calcd for C₂₇H₃₇N₄O₁₆PSNa (M + 2 H + Na)⁺: 759.1559. Found: 759.1545.