Approaches to the Synthesis of Glycosides

In a search for better synthetic routes to O- and S-glycosides, a number of mercury(II) containing derivatives of 1-thio-D-glucose were synthesised, and their reactions with thiols and acids were investigated as well as their pyrolytic behaviour. A new route to O-acetylated glycosyl thiols involving specific S-deacetylation of peracetylated 1-thioglycoses was developed by the conversion of 1-thio-Beta-D-glucopyranose pentaacetate into tetra-O-acetyl-1-S-phenylmercury (II) thio-Beta-D-glucopyranose and subsequent demercuration of this by hydrogen sulphide. A range of acylated alkyl and aryl 1,2-trans-1-thioglycosides was prepared by one step processes from peracylated 1,2-trans-related sugars by a procedure which involved the use of equimolar proportions of thiols together with boron trifluoride. A similar procedure was used to obtain benzoylated 1,2-cis-O-glucosides from penta-O-benzoyl-Beta-D-glucopyranose. Partial desulphurisation of acetylated glucosyl phenyl disulphide with tris(diethylamino)phosphine led to both phenyl tetra-O-acetyl-1-thio-alpha-D-glucopyranoside and the alpha, beta-linked thiotrehalose peracetate. Phenyl 1-thiohex-1-enopyranosid-3-ulose esters were obtained from the light induced reactions of N-bromosuccinimide with acetylated and benzoylated phenyl 1-thiogluco- and galacto-pyranosides; the acetylated 1-thioglycosides gave mixtures of 2-O-acetyl and 2-O-monobromoacetyl 1-enosid-3-uloses. Methyl hexuronate derivatives were brominated alpha to the carbonyl function by N-bromosuccinimide, and a new synthetic route to L-ascorbic acid has been proposed following the successful bromination of methyl tri-O-acetyl-2,6-anhydro-L-gulonate.