Saccharides trichloroacetimidates

Glycosides and Saccharides from Acetylated Glucosyl Trichloroacetimidates... 

Acid-catalyzed allylation with allyl trichloroacetimidate was used to protect the hydroxyl group without migration of any acyl group present in the molecule of saccharide [89]. Thus, methyl 3,4-di-O-allyl-2,6-di-0-benzoyl-oc-D-mannopyranoside was obtained from the corresponding dibenzoate in 68% yield using trifluromethane-sulfonic acid as a catalyst. 

The trichloroacetimidate methodology has been successfully applied to the synthesis of sialyl and asialyl TN epitopes (Scheme 5.9).29 The use of this methodology can lead to predominant orthoester formation with 2-(9-acetyl protected glycosyl donors, but acceptable results can be obtained with 2-azido-glycosyl donors. The complexity of the tetra-saccharide donor probably contributes to the poor chemical yield of this... 

Adinolfi, M, Barone, G, Guariniello, L, ladonisi. A, Efficient activation of armed glycosyl trichloroacetimidates with Sm(OTf)3 in the stereoselective glycosidation of saccharidic acceptors. Tetrahedron Lett., 41, 9005-9008, 2000. 

Schmidt RR, Jung KH (2000) Trichloroacetimidates. In Ernst B, Hart GW, Sinay P (eds) Carbohydrates in Chemistry and Biology, Part I Chemistry of Saccharides, vol 1. Wiley-VCH, Weinheim, p 5... 

Trichloroacetimidates function well as donors also with saccharide thiol acceptors. A number of thiodisaccharides have accordingly been prepared using this method [169,170,171,172,173], Possible by-products are various elimination products and orthoester formation. The stereochemical outcome is not easy to predict or control and, as so often in carbohydrate chemistry, an optimization of conditions is usually necessary for each glycosylation. For example, the use of an acetylated o -trichloroacetimidate glucose donor can yield not only an almost exclusively -linked disaccharide product but also preferentially an a-linked product, depending on the acceptor and conditions used ( Scheme 53) (see also Sect. 3.3). 

The Trichloroacetimidate Method Application to Glycoside and Saccharide Synthesis... 

The base-catalyzed addition of alcohols to nitriles to give imidates proceeds well, if there are electron-attracting groups in the a-position. In such cases the Pinner synthesis is less effective, because nitrile basicity is less. TTiis shows that both methods are complementary. Recently attention has been paid to the long-known addition of alcohols to trichloroacetonitrile, since it was found that imidates prepared from protected saccharides, amino alcohols etc. and trichloroacetonitrile are useful reagents for the synthesis of nucleosides, disaccharides and other natural products. The trichloroacetimidic acid esters (240 equation 131) of fluorinated, unsaturated aliphatic alcohols °° and benzyl alcohol have been prepared for synthetic purposes. 

Up to now, many effective methods have been developed for the coupling reaction of primary alcohols with saccharides (e.g., the Koenigs-Knorr reaction or the trichloroacetimidate method) (41). The coupling of long-chain, branched, secondary alcohols with glycosides has offered more problems subsequently, fewer approaches toward the development of these products have been made (42). Therefore, we started to explore the oleochemistry and the potential use of two secondary hydroxy fatty acid esters, namely, methyl 9- [4] and methyl 12- hydroxyoctadecanoate [5]. 

Scheme 1. SPOS - O-Glycosyl trichloroacetimidates as glycosyl donors, S = Saccharide, L = Linker, P = Polymer support.

---