The on-going exploration of thiol-based carbohydrate leaving groups have led us to the heterocyclic compound 2-mercapto-6-methylpyridine. The leaving group was affixed to the pyranose series containing glucose, galactose, and mannose. The leaving group was subjected to a variety of thiophilic promoters to determine ability to be utilized in chemical glycosylation. Iodine, Dimethyl(methylthio)sulfonium trifluoromethanesulfonate (DMTST), copper(II) triflate (Cu(OTf)2), silver(I) triflate (AgOTf), silver(I) perchlorate (AgClO4) were selected due to their known uses toward glycosidation. Although reactivity rates varied, the copper and silver-based promoters activated the mercaptopyridine moiety readily. Conversely, iodine exhibited little to no reactivity in the coupling reaction. This in turn led to a convenient one-pot orthogonal glycosylation strategy with sugars bearing S-ethyl leaving groups. A glycosyl donor bearing the mercaptopyridine leaving group was couple with an acceptor containing an anomeric S-ethyl in the presence of AgOTf. Upon completion of this glycosylation, a trisaccharide was reached by the addition of I2 and a new glycosyl acceptor containing mercaptopyridine. Additional oligosaccharides strategies are being pursued containing this interesting 2-mercapto-6-methylpyridine leaving group.

6-Methylpyrid-2-yl as a thiol-based carbohydrate leaving group

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