Facile Formation of Novel Carbohydrate-Amino Acid Conjugates by Reductive Amination

Abstract

Coupling of amino acids with aldehyde functionalised carbohydrate derivatives by reductive amination led to novel carbohydrate-amino acid conjugates.

Key words

ozonolysis - carbohydrate-aldehydes - amino acids - reductive amination - glycosidases

References

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9

All reductive aminations were accomplished as follows: 1 mmol of aldehyde and 1.2 mmol of amine were solved in 8 mL of a 50 mM K₃PO₄ buffer, pH 7.0, and after 1 h 1 mmol NaBH₃CN was added. Stirring at r.t. was continued for 3 d, then the solution was lyophilised and the compounds separated on a biogel P2 column with water as eluent.

13

The enzymatic galactosylation was performed as follows: 0.2 mmol galactosyl donor and 1 mmol allyl 2-acetamido-2-deoxy-α-d-glucopyranoside were dissolved in 4 mL of a 50 mM potassium phosphate buffer. 636 µL (33 U) β-galactosidase from B. circulans were added and after 1 d stirring at r.t., the enzyme was denaturated by heating at 100 °C for 5 min. The reaction mixture was lyophilisised. Purification of the product was achieved by chromatography on biogel P2 with water as eluent.

15

The enzyme-catalysed oxidation was accomplished as follows: 200 mg (0.66 mmol) pNP β-d-galactopyranoside were solved in 10 mL of a 50 mM potassium phosphate buffer, pH 7.0. Then 10 µL of a 500 mM CuSO₄ solution, 90 µL (3120 U) catalase and 90 µL (90 U) galactose oxidase were added subsequently and the reaction mixture stirred under oxygen for 3 d. To this mixture 4 mL methanol were added and after 15 min of stirring the solvent was evaporated. The residue was purified by column chromatography on silica gel with dichloromethane/methanol 9:1 as eluent.

16

Selected spectral data for 29: ¹H NMR (400 MHz, D₂O): δ = 5.87 (ddd, 1 H, CH-All), 5.26 (d, 1 H, = CH₂-All), 5.17 (dd, 1 H, = CH₂-All), 4.84 (d, 1 H, H-1), 4.44 (d, 1 H, H-1′), 4.12 (dd, 1 H, -CH₂-All), 3.95 (dd, 1 H, -CH₂-All), 3.90 (dd, 1 H, H-2), 3.88-3.70 (m, 7 H, H-3, H-4, H-5, H-6a, H-6b, H-4′, H-5′), 3.60 (dd, 1 H, H-3′), 3.47 (dd, 1 H, H-2′), 3.42 [dd (t), 2 H, -CH₂-a], 3.35 (m, 1 H, H-6a′), 3.29 (dd, 1 H, H-6b′), 3.20 [dd (t), 2 H, -CH₂-b], 1.96 (s, 3 H, NHAc)ppm. Coupling constants: J _1,2 = 3.6, J _2,3 = 10.4, J _{1 ′ ,2 ′} = 7.6, J _{2 ′ ,3 ′} = 9.7, J _{3 ′ ,4 ′} = 3.3, J _{5 ′ ,6a ′} = 8.4, J _{5 ′ ,6b ′} = 3.1, J _{6a ′ ,6b ′} = 13.2, J _CH2-a,CH2-b = 6.6, J _CH-All, = _CH2c = 10.7, J _CH-All, =J _CH2t = 17.3, J _{CH-All,CH2-All} = 6.1, J _{CH2-All,CH2-All} = 13.0 Hz. ¹³C NMR (100 MHz, D₂O): δ = 174.79 (NHAc), 133.93 (CH-All), 118.33 (=CH₂-All), 102.71 (C-1′), 96.18 (C-1), 77.09 (C-4), 72.51 (C-3′), 71.28, 71.07, 70.47, 69.96, 69.62 (C-3, C-5, C-2′, C-4′, C-5′), 68.95 (-CH₂-All), 60.05 (C-6), 53.84 (C-2), 48.81 (C-6′), 46.88 (-CH₂-b), 43.95 (-CH₂-a), 22.23 (NHAc) ppm. MALDI-TOF (DHB): m/z = 531.37 (M + H⁺), 553.36 (M + Na⁺), 569.33 (M + K⁺), 575.34 (M + 2 Na⁺ - H⁺), 591.32 (M + Na⁺ + K⁺ - H⁺), 607.30 (M + 2 K⁺ - H⁺).