Ungesättigte Zucker. Eine milde Sulfonat‐β‐Eliminierung bei Aminohexopyranosiduronat‐Derivaten

Abstract

AbstractSubstituted 2‐deoxy‐2‐acylamino‐4‐O‐methanesulfonyl‐hexopyranosiduronates yield, by mild alkaline mesylate (a, e)‐β‐elimination, the corresponding 4,5‐unsaturated 4‐deoxyhexopyranosiduronates VIII. This type of aminosugars proved to be the cyclic enol‐ether acetal form of the 2,4‐dideoxy‐2‐acylamino‐hexos‐5‐ulosuronates. The structural principle of the latter can be found e.g. in neuraminic acid.These 4,5‐unsaturated 4‐deoxy‐acylamino‐hexopyranosiduronates give by reduction with NaBH4 the corresponding 4,5‐unsaturated 2,4‐dideoxy‐2‐acylamino‐hexopyranosides IX (with an endocyclic double bond on the glycosidic C atom 5).The isomeric 5,6‐unsaturated 2,6‐dideoxy‐2‐acylamino‐hexopyranosides XVI (with an exocyclic double bond) are furthermore synthesized according to the method of HELFERICH [14] by elimination of a molecule of HI from the corresponding 2,6‐dideoxy‐2‐acylamino‐6‐iodo‐4‐O‐acylhexopyranoside derivatives XV.The ring stability of the two types of isomeric unsaturated hexopyranosides mentioned (bearing respectively an exo‐ and an endocyclic 5‐enol‐ether linkage) has been examined. In accordance with the stability principle of BROWN [16] – on the base of our preliminary experimental indications – the hexopyranosides with endocyclic double bond have been shown to be more stable than those with an exocyclic double bond: the latter (1) decompose slowly at 20°; (2) the α‐glycosidic linkage is very easily split by dil. acetic acid at 20° within a few hours, giving 2, G‐dideoxy‐2‐acyl‐amino‐D‐xylo‐hcxofuranos‐5‐ulose derivatives XX. On the other hand, the hcxopyranosides with endocyclic double bond show in the mass spectrometer, besides other fragmentations, a retro‐dien decomposition.Some data on the NMR. spectra (100 and 220 MHz) of the above isomeric unsaturated acylamino‐hexopyranosides (and hexopyranosiduronates, resp.) are furnished. The ORD./CD. spectra of the 4,5‐unsaturated 2,4‐dideoxy‐2‐acylamino‐hexopyranosiduronates, which have two «COTTON centres», have been measured.