title: A total synthesis of hydroxylysine in protected form and investigations of the reductive opening of p-methoxybenzylidene acetals.
abstract: A synthesis of (2S,5R)-5-hydoxylysine, based on (R)-malic acid and Williams glycine template as chiral precursors, has been developed. This afforded hydroxylysine, suitably protected for direct use in peptide synthesis, in 32% yield over the 13-step sequence. Regioselective reductive opening of a p-methoxybenzylidene acetal and alkylation of the Williams glycine template were key steps in the synthetic sequence. Surprisingly, the regioselectivity in opening of the p-methoxybenzylidene acetal was reversed as compared to what was expected. It was found that this was due to chelation of the trialkylsilyl choride, used as an electrophile in the reductive opening, to an adjacent azide functionality. It was also discovered that an equivalent amount of trialkylsilyl hydride was formed in the reaction, a finding that led to additional mechanistic insight into reductive openings of p-methoxybenzylidene acetals with sodium cyanoborohydride as reducing agent.
authors.affiliation: Organic Chemistry, Department of Chemistry, Umeå University, SE-901 87 Umeå, Sweden.
authors.forename: Tomas
authors.initials: T
authors.lastname: Gustafsson
authors.forename: Magnus
authors.initials: M
authors.lastname: Schou
authors.forename: Fredrik
authors.initials: F
authors.lastname: Almqvist
authors.forename: Jan
authors.initials: J
authors.lastname: Kihlberg
mesh_terms: D000080:Acetals / Q000138:chemical synthesis / Q000737:chemistry*; D000478:Alkylation; D001597:Benzylidene Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D006901:Hydroxylysine / Q000138:chemical synthesis*; D015394:Molecular Structure; D010084:Oxidation-Reduction; D013237:Stereoisomerism
chemical_list: D000080:Acetals; D001597:Benzylidene Compounds; D006901:Hydroxylysine