5- Thio-D-mannose

Thio-D-mannose (638), the first example of a naturally occurring 5-thio-sugar has been isolated from Clathria pyramida [504] and was later synthesised in 12 steps from D-mannose [505]. 

Capon, R. J. and MacLeod, J. K., 5-Thio-D-mannose from sponge Clathria pyramida (Lendenfeld). First example of a naturally occurring 5-thiosugar., J. Chem. Soc., Chem. Commun., 1200, 1987. 

In the realm of thiosugars, the only pyranose known to be a natural product is 5-thio-D-mannose 7 (Figure 9.2), but more complex structures, salacinol 8 and cotalanol 9, have recently been found in plants known for their antidiabetic properties in Indian folk medicine. 

Thio-D-mannose 7, discovered as a metabolite of the marine sponge Clathria pyramida (Lendenfeld), is still unique as the only example of a 5-thioaldopyranose occurring in nature [45]. Shortly after its discovery, a synthesis from methyl 2,3 5,6-di-0-isopropylidene-a-D-mannofurano-side was reported [46], which essentially followed the principle of the approach depicted in Scheme 9.1. Earlier, 5-thio-D-mannose had been available by molybdate catalyzed epimerization [47,48] of 5-thio-D-glucose 10 [37]. 

Yuasa, H, Izukawa, Y, Hashimoto, H, Synthesis of 5-thio-D-mannose, J. Carbohydr. Chem., 8, 753-763, 1989. 

Most of the other important 5-thiopyranoses such as 5-thio-D-mannose (32) [55], 5-thio-D-galactose (33) [56], and 5-thio-D-allose [57] have been synthesized. 

Thio-D-mannose (3), isolated from a marine sponge, is the first S-thiosugar to be found in Nature. Its thesis from D-mannose, which is outlined in Scheme 2, involves two stereochemical inversions at C-5. Another new thiosugar, methyl 2.6-dideoxy-4-thio-a-D-ribo-hexopyranoside (5), a constituent of the calichemycins, a new class of antitumour antibiotics, has been prepared from the... 

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