Purines, pyrimidines, and imidazoles. Part 49. Adenine and imidazole nucleosides of D-mannofuranose

Abstract

Reaction of 2,3:5,6-diO-isopropylidene-D-mannofuranosylamine with ethyl N-[carbamoyl(cyano)methyl]-formimidate gave crystalline 5-amino-1-(2,3:5,6-di-O-isopropylidene-α- and -β-D-mannofuranosyl)imidazole-4-carboxamides, treatment of which with phosphoryl chloride in chloroform produced 5-amino-4-cyano-1-(2,3:5,6-di-O-isopropylidene-α- and -β-D-mannofuranosyl)imidazoles. The anomeric aminonitriles with triethyl orthoformate followed by ethanolic ammonia led directly to 9-(2,3:5,6-di-O-isopropylidene-α- and -β-D-mannofuranosyl)adenines which with acid gave sequentially 9-(2,3-O-isopropylidene-α- and -β-D-mannofuranosyl)adenines and 9-α- and -β-D-mannofuranosyladenines. The two latter α-anomers were identical with specimens prepared by another route. The structures of the mannofuranosyladenines were confirmed by periodate oxidation followed by reduction with sodium borohydride and comparison of the specific rotations of derived glycerol derivatives with those produced by adenosine, and by n.m.r. and c.d. studies. ¹H N.m.r. spectra of comparable pairs of anomeric mannofuranosyl imidazoles and 2′,3′-O-isopropylidenemannofuranosyladenines showed that they did not accord with an empirical rule relating anomer configuration with the field positions of 1′-H whereas 9-(2,3:5,6-di-O-isopropylidene-α- and -β-D-mannofuranosyl)adenine or 9-α- and -β-D-mannofuranosyladenine anomer pairs had spectral relationships in accord with the rule.