Ribopyranoside, methyl 1,5-dithio

C6H12O3S2 0.25 H20 Methyl 1,5-dithio-a-D-ribopyranoside, tetartohydrate MDTRPY20 32 358... 

The reaction of p-D-ribopyranose tetraacetate (63) with methanethiol and zinc chloride gave 32), after deacetylation, methyl 1-thio-p-D-ribo-pyranoside (64), methyl 1,5-dithio-p-D-ribopyranoside (72, R=H), 4-S-methyl-4-thio-L-lyxose dimethyl dithioacetal (77, R=H), and a small... 

The other two known examples of intramolecular H-bonds within a monosaccharide unit in the crystalline state occur in two thio-sugars, methyl-l-thio and methyl-1,5-dithio-a-D-ribopyranoside (40) (illustrated in Figure 3). As far as we know, these are the first examples of syn-diaxial O-H O bonding in a cyclic carbohydrate in the solid state. It is not certain now, whether any particular significance should be associated with the fact that these are thio sugars. 

Fig. 13.8. Details of the intramolecular hydrogen bonds in the two symmetry-independent molecules in the crystal structure of methyl 1,5-dithio-o-ribopyranoside quarterhydrate [MDTRPY20]...

The -D chair conformation is also stabilized in the crystalline state by the formation of an intramolecular hydrogen bond in both methyl-1,5-dithio-a-ribopyranoside quarterhydrate [MDTRPY20] and methyl-1-thio-a-ribopyranoside [MTRIBP 10]. In the former structure there are two symmetry-independent molecules with different directions for the 0(2)H to 0(4)H bond, as shown in Fig. 13.8. In the methyl-1 -thio-a derivative the direction is 0(2)H 0(4) and the bond forms part of an infinite chain, as shown in Fig. 13.9. In the methyl-1,5-dithio-a-ribopyranoside quarterhydrate, the hydrogen-bond direction is 0(4)H 0(2) in one molecule and 0(2)H 0(4) in the second crystallograph-ically independent molecule in the same crystal structure. As shown in Fig. 13.10, the intramolecular hydrogen bond is part of a cyclic arrangement of eight bonds,... 

Conversion of tetra-0-acetyl-/3-D-ribopyranose into methyl 1-thio-/3-D-ribopyranoside, by the action of methanethiol and zinc chloride, with subsequent deacetylation, is accompanied by the formation of substantial proportions of methyl l,5-dithio-j8-D-ribopyranoside (55) and 4-S-methyl-4-thio-L-lyxose dimethyl dithioacetal (53), plus a trace of 5-S-methyl-5-thio-D-ribose dimethyl dithioacetal (56). Although similar treatment of tetra-O-acetyl-jS-D-ribofuranose for a short time produced the expected methyl 1-thio-jS-D-... 

P2,2,2i Z = 4 Dx = 1.479 R = 0.07 for 660 intensities. The conformation is C4, with three axially attached hydroxyl groups, two of which, O-2-H and O-4-H, are linked by an intramolecular hydrogen-bond. Similar intramolecular hydrogen-bonding has been observed in the crystal structures of methyl 1-thio-a-D-ribopyranoside and methyl 1,5-dithio-a-D-ribopyranoside.13 This is the same crystal structure as that given in a preliminary report,14 which did not include the atomic parameters. 

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