Stereocontrolled routes to cis-hydroxyamino sugars. Part VI. A synthesis of garosamine

Abstract

A common subunit of novel potent antibiotics, modifications of C-gentamicins, is the amino sugar garosamine. The exocyclic olefin, 5, obtained from the known epoxy uloside, methyl 2,3-anhydro-.beta.-D-erythro-pentopyranosid-4-ulose, 3, reacts with ammonia or methylamine to give the 3-amino-3-deoxy or 3-methylamino-3-deoxy derivatives, respectively. The benzamide, 8c, obtained from the former, reacts with iodonium ion to give an oxazolone in which the cis relationship between the tertiary alcohol and the 3-amino group of garosamine is secured. Deiodination is followed by a one-pot N-methylation and reduction. A hydrolysis gives methyl .alpha.-L-garosamimide 2. In a 2nd route, the urethane, 16c, reacts with iodonium ion to given an oxazolidone 17a. This reaction establishes the cis-hydroxyamino moiety and circumvents the N-methylation/reduction steps. Deiodination followed by deprotection yields 2. Both routes require 8 steps from 3 with overall yields of 14% and 11%, respectively.