Improved synthesis and the crystal structure of methyl 4,6-dideoxy-4-(3-deoxy- l- glycero-tetronamido)-α- d-mannopyranoside, the methyl α-glycoside of the intracatenary repeating unit of the O-polysaccharide of Vibrio cholerae O:1

Abstract

The crude product of deamination of the commercially available l-homoserine was acetylated and the 2- O-acetyl-3-deoxy- l- glycero-tetronolactone (18) formed was used to N-acylate methyl perosaminide (methyl 4-amino-4,6-dideoxy-α- d-mannopyranoside, 12) and its 2,3- O-isopropylidene derivative. The major product isolated from the reaction was the crystalline methyl 4-(4- O-acetyl-3-deoxy- l- glycero-tetronamido)-4,6-dideoxy-α- d-mannopyranoside ( 1, 70–75%) resulting from acetyl group migration in the initially formed 2'- O-acetyl derivative. O-Deacetylation of 1 gave the title amide 2. Compound 2, obtained crystalline for the first time, was fully characterized, and its crystal structure was determined. Deoxytetronamido derivatives diastereomeric with 1 and 2, respectively, were obtained by the acylation of 12 with 2- O-acetyl-3-deoxy- d- glycero-tetronolactone (prepared from d-homoserine), and subsequent deacetylation. Structures of several byproducts of the reaction of 12 with 18 have been deduced from their spectral characteristics. Since these byproducts were various O-acetyl derivatives of 2, the title compound could be obtained in ≈ 90% yield by deacetylating (Zemplén) the crude mixture of N-acylation products, followed by chromatography.