Confirmation of the structures of the products obtained on acylation of 2-amino-2-deoxy-D-gluconic acid.

Acetylation of 2-amino-2-deoxy-D-gluconic acid (1) with acetyl chloride-pyridine gave 2,3-unsaturated six- and five-membered lactones (2 and 3). Their benzoylated analogs (4 and 5) were obtained by benzoylation of 1 with benzoyl chloride-pyridine. Reaction of 1 with hot acetic anhydride-sodium acetate gave a approximately 1:2 mixture of (E)- and (Z)-2-acetamido-6-acetoxyhexa-2,4-dien-4-olide (6-E and 6-Z). Treatment of 3 with 1,8-diazabicyclo[5.4.0]undec-7-ene also gave as the main product 6-Z, which was isolated crystalline from the reaction mixture. The same reaction applied to compound 5 gave selectively the Z-isomer of the benzoylated furanone 7. Partial and total hydrogenation (H2-Pd-C) of the mixture 6-E, Z gave, respectively, a racemic monounsaturated lactone (8) and a dideoxy lactone (9), for which the threo-configuration for the chiral centers at C-2 and C-4 was determined. Acidic removal of the acetyl groups from 9 afforded the 2-amino-6-hydroxy-1,4-lactone hydrochloride 10. On the other hand, acetylation at high temperature of the 4,6-O-benzylidene derivative of 1 (11) gave the 2,3-unsaturated, six-membered lactone (12), precursor of 2-acetamido-6-acetoxyhexa-2,4-dien-5-olide (14).