Effect of isomers of swainsonine on glycosidase activity and glycoprotein processing

Abstract

The chemical synthesis of swainsonine [(1S,2R,8R,8.alpha.R)-trihydroxyindolizidine] from trans-1,4-dichloro-2-butene was previously described [Adams, C. E., Walker, F. J., and Sharpless, K. B. (1985) J. Org. Chem. 50, 420-424]. A modification of that synthesis provided two other isomers, referred to here as "Glc-swainsonine" [(1S,2S,8R,8.alpha.R)-trihydroxyindolizidine] and "Ido-swainsonine" [(1S,2S,8S,8.alpha.R)-trihydroxyindolizidine]. To determine whether these new compounds had biological activity, they were compared to swainsonine as inhibitors of a number of commercially available glycosidases. Whie swainsonine is a potent inhibitor of jack bean .alpha.-mannosidase but does not inhibit other glycosidases, its two isomers were inactive on .alpha.-mannosidase but did inhibit other enzymes. Thus, Glc-swainsonine was an inhibitor of the fungal .alpha.-glucosidase amyloglucosidase, and this inhibition was of a competitive nature (Ki = 5 .times. 10-5 M) with respect to the substrate p-nitrophenyl .alpha.-D-glucopyranoside. This alkaloid also inhibited .beta.-glucosidase, but much less effectively than .alpha.-glucosidase. On the other hand, Ido-swainsonine was more effective toward .beta.-glucosidase than toward .alpha.-glucosidase, and this inhibition was also of a competitive nature. None of these inhibitors were effective against .beta.-mannosidase or .alpha.- or .beta.-galactosidase. Glc-swainsonine was also tested against the glycoprotein processing glycosidases. Surprisingly, in this respect, the alkaloid was like swainsonine in that it inhibited mannosidase II but had no effect or only slight effect on glucosidase I, glucosidase II, and mannosidase I. Glc-swainsonine also inhibited glycoprotein processing in cell culture. The oligosaccharide or oligosaccharides produced in the presence of Glc-swainsonine were hybrid types of structures similar to those seen in the presence of swainsonine and clearly different from oligosaccharides induced by either castanospermine or deoxymannojirimycin. The inhibition of processing and of mannosidase II could not be due to the presence of swainsonine in the Glc-swainsonine preparation, since this material did not inhibit jack bean .alpha.-mannosidase, even at 10 .mu.g/mL.