Acylating properties of N-substituted 2-C:1-N-carbonyl-2-deoxyglycopyranosylamines

✍ Scribed by Danuta Mostowicz; Marek Chmielewski

• Publisher: Elsevier Science
• Year: 1994
• Tongue: English
• Weight: 555 KB
• Volume: 257
• Category: Article
• ISSN: 0008-6215
• DOI: 10.1016/0008-6215(94)84114-4

✦ Synopsis

Recently, we reported that the unstable [2 + 2lcycloadducts (1) of tosyl [1,2] or trichloroacetyl [3,4] isocyanate and glycals, upon treatment with alcohols or water, underwent rapid opening of the four-membered ring at the anomeric carbon atom to afford glycosides having alkoxyl and carbamoyl functions located anti (Scheme 1) [l-41.

In this paper, we demonstrate that the direction of the attack of nucleophiles at 2-C : l-N-carbonyl-2-deoxyglycopyranosylamines

[5] depends on the electronegativity of the Z-substituent at the nitrogen atom. To illustrate this phenomenon, we selected four compounds (S-8) of a-D-gluco configuration, bearing an N-acyl substituent having less electron-withdrawing character than a sulfonyl or trichloroacetyl substituent.

The tetraacetate 5 was obtained by peracetylation of the unsubstituted compound 2 161, whereas the N-acetyl (61, N-ethoxycarbonyl (71, and N-carbamoyl (8) derivatives were obtained by direct acylation of the p-lactam nitrogen atom in 4 with acetic anhydride, ethyl chloroformate, and trichloroacetyl isocyanate, respectively. Compound 7 could also be obtained by high-pressure [2 + 2lcycloaddition of ethoxycarbonyl isocyanate to tri-O-benzyl-D-glucal [7].

Compounds 5-8, when dissolved in methanol and left overnight at room temperature, afforded the respective methyl esters 9-12 in good or moderate yield. The same direction of opening was observed when the N-acyl compounds 5-8 were treated with benzylamine, hexylamine, or the methyl ester of glycine. The products 9, 10, 13, 14, 17, and 18 derived from the iV-acetyl compounds 5 and 6 were contaminated with the corresponding N-deprotected compounds 3 and 4. Opening of the four-membered p-lactam ring at the anomeric carbon atom is an S, type reaction and requires a good leaving group at the place of substitution.