Mannopyranoside ethyl 1-thio-, preparation

Zervas48 through the catalytic reduction of 2,3,4,6-tetraacetyl-2-hydroxy-D-glucal, has recently been prepared by the reductive desulfurization of ethyl tetraacetyl-l-thio-/ -D-mannopyranoside (XL),47 a substance which has been obtained through the mercaptolysis of mannosidostreptomycin48 and may be prepared through the prolonged action of ethyl mercaptan and hydrochloric acid on D-mannose. 

The disaccharide epitope a-Tyv-(l —>3)-a-o- Man present in the D1 Salmonella serotype was synthesized as the pentenyl glycoside. The tyvelose donor 138 was prepared from ethyl l-thio-p-o-mannopyranoside 137 employing a single dideoxygenation step (Scheme 40). Glycosylation of 138 with the mannopyranosyl... 

Mercaptolysis of /3-D-glucopyranose pentaacetate in ethyl mercaptan at 0°, with zinc chloride as catalyst, gives ethyl tetra-O-acetyl-l-deoxy-1-thio-/S-D-glucopyranoside in 71% yield. Under the same conditions, a-D-glucopyranose pentaacetate reacted only very slowly, but it could be shown that the deoxy-thio-/3-D-glucoside is formed in much greater amount than is the a anomer. Mercaptolysis of the D-mannopyranose pentaacetates under the same conditions for 48 hours resulted in a 70% yield of ethyl tetra-O-acetyl-l-deoxy-l-thio-a-D-mannopyranoside from the /3-D-pentaacetate, and in a 60% yield from the a anomer.103 Inspection, by preparative paper chromatography, of the residual sirups, after deacetylation, led in each case to the isolation of the anomeric ethyl-1-... 

Preparation of (2 5, 3 S )-ethyl-3,4-0-[2, 3 -dimethoxybutan-2, 3 -diyl]-I-thio-a-D-mannopyranoside. 

Preparation of ethyl 2,3,4,6-tetra-O-acetyl-l-thio-a-D-mannopyranoside S -oxide (18) [142]. 

Acetamido-4-amino-2,4,6-trideoxy-D-galactopyranosyl precursors such as trichltHoacetimidate 76, were prepared from ethyl 1-thio-a-D-mannopyranoside. Key steps were stereoselective reduction of oxine 74 (available in 5 steps), and azidonitration of glycal 75 (Scheme 23). Their application in the synthesis of disaccharides is covered in Chapter 3. Benzyl 2,4-diacetamido-3-6>-benzyl-2,4,6-trideoxy-P-D-galactopyranoside has been synthesized in 5 steps from benzyl 2-acetamido-3-6>-benzyl-2-deoxy-P-D-galactopyranoside. ... 

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