Synthese von (+)-Castanospermin und 1-Epicastanospermin aus D-Glucofuranurono-6,3-lacton durch Reformatsky-Reaktion

Synthesis of (+)‐Castanospermine and 1‐Epicastanospermine from D‐Glucofuranurono‐6,3‐lactone by Reformatsky Reaction Starting from 5‐O‐(tert‐butyldimethylsilyl)‐1,2‐O‐isopropylidene‐α‐D‐gluco‐ (2a) or ‐β‐L‐idofuranurono‐6,3‐lactone (2b), 7‐deoxyoctofuranose derivatives 5a, 5b, 7a and 7b have been synthesized by chain extension at C‐6 by Reformatsky reaction followed by reduction with calcium borohydride. The respective configuration of the products was determined by transformation into the known 7,8‐dideoxyoctofuranoses 5o, 5p, 7k and 7l. From the mixture of 7a and 7b, formed in a proportion of approximately 4:1, the glycosidase inhibitors (+)‐castanospermine (1a) and 1‐epicastanospermine (1b) have been prepared in 8 and 9 simple steps, respectively, in overall yields of 33.4 and 9.5%.