名称:
Towards cyclic, conformationally constrained, fluorine-containing β-amino acid derivatives from d-glucose
摘要:
Novel, potentially bioactive. fluorinated branched-chain monosaccharides were obtained by reaction of diethylaminosulphur trifluoride (DAST) with a series of methyl 3-C-cyano-3-ethoxycarbonyl-beta -D-glucopyranoside derivatives including the 4,6-O-benzylidene derivative and their 3-C-(N-protected aminomethyl) reduction products, as well as the phenyl 3-C-cyano-3-ethoxycarbonyl-1-thio-alpha -D-(and beta -D-)glucopyranosides, The absolute configuration at C(3) was unambiguously assigned for all Compounds on the basis of X-ray crystallographic analysis of methyl 4,6-O-benzylidene-3-C-cyano-3-deoxy-3-ethoxycarbonyl-beta -D-glucopyranoside, corroborating the previous tentative assignment by other authors for the 4,6-unprotected Compound. The course of the fluorination depended on the reaction temperature and the substitution pattern of the Substrate. Thus. for methyl 3-C-cyano-3-ethoxycarbonyl-beta -D-glucopyranoside, fluorination occurred exclusively at C(6), but for the phenylthio analogue. a 2-deoxy-2-phenylthio-alpha -D-manno-configured glycosyl fluoride and its 6-fluoro derivative were obtained, resulting from the expected rearrangement reaction. whilst starting from the phenylthio alpha anomer. only the Unrearranged 6-fluoro compound was formed. Rearrangement was also observed in the fluorination of methyl 4,6-O-benzylidene-3-C-(N-protected aminomethyl)-beta -D-glucopyranoside, which led to the 2-O-methyl-alpha -D-mannopyranosyl fluoride derivative as the sole product. This methodology may constitute a simple route to enantiopure conformationally constrained cyclic fluorinated beta -amino acids having the alpha carbon atom shared with a pyranose ring, although only moderate yields were achieved. particularly in the fluorination step. (C) 2001 Elsevier Science Ltd. All rights reserved.