Regioselective metallation and amination of monosaccharides
A number of reactions of monosaccharides, mainly derivatives of xylose and glucose, have been carried out. These reactions have involved metallation, by the use of stannylating and boronating agents, and amination. These metallated and aminated derivatives are of synthetic use and therefore have been subjected to further reaction. Both 0-stannylation and C-stannylation of monosaccharides have been studied and reported. O-Stannylation was carried out by reaction of the appropriate monosaccharide or polyol with either diorganotin oxide, to give a cyclic stannylene derivative, or bis-triorganotin oxide, to give the triorganotin ether, in benzene with azeotropic removal of water. The O-stannylated products were then reacted with acylating and alkylating reagents in a variety of reaction media in order to determine the optimum conditions and solvents for regioselective mono-substituion for each reagent. Also the structures of the cyclic stannylenes were investigated and a possible structure for the dibutylstannylene derivative of methyl D-xylopyranoside proposed. The possibility of D-phosphorylation of a polyol via its dibutylstannylene derivative was studied. C-Stannylation of monosaccharides can occur via anhydro- ring opening with use of an activated triorganotin-lithium compound as the stannylating agent. The use of a tosylated derivative would mean that the stannylation reaction can be carried out without initially producing the anhydro-sugar. The use of this route to produce a C-stannylated monosaccharide has been proven. 0-Boronation of monosaccharides was carried out by reacting the required monosaccharide with arylboronic anhydride (0.33 equivalents) in benzene with azeotropic removal of water. The use of the 0-boronated compounds in synthesis has been studied and the use of the arylboronate group as a protecting group in carbohydrate synthesis evaluated. Furthermore a comparison of the diorganostannylene and arylboronate derivatives of methylo-D-glucopyranoside in a variety of reaction conditions has been made. Protected and partially protected glucopyranosylamines are of great interest in carbohydrate chemistry as they can be used as the precursors of glucosylthioureas and glucosylaminoheterocycles which are W-nucleoside analogues. A series of protected glucopyranosylamines were prepared and these were used in the synthesis of these biologically important derivatives. Also a disaccharide derivative of the intermediate protected glucopyranosylenamine was produced. All products, where possible, were characterised by 1H and 13C n.m.r.