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5- and 4-(d-lyxofuranosyl)pyrazoles: a new type of pyrazole C-nucleoside

✍ Scribed by Manuel Gómez-Guillén; José María Lassaletta Simon

Publisher
Elsevier Science
Year
1993
Tongue
English
Weight
403 KB
Volume
239
Category
Article
ISSN
0008-6215

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✦ Synopsis

C-Nucleosides and their analogues constitute targets in organic synthesis because of their biological and pharmacological properties. A convenient route to this type of compound involves the well-known acid-catalysed cyclodehydration of polyhydroxyalkyl chains bonded to heterocycles1-8. Thus, in the presence of trifhroroacetic acid as catalyst, 3-(mnanno-or D-gala&-pentitol-1-yl)pyrazole

(1 or 2) was dehydrated'*r' to give 3-(D-arabinofuranosyl~ (3) or 3-(D-lyxofuranosyl)pyrazole (41, respectively, in moderate to good yields. To the best of our knowledge, l-substituted pyrazole C-nucleosides having the sugar moiety at C-5 or C-4

have not yet been described and we now report their preparation.

The starting compounds used for the cyclodehydration were l-methyl (or phenyljpyrazole derivatives having a D-gahc@-pentitol-l-y1 chain at C-5 (5 and 6) or at C-4 (7). These compounds were prepared'r by deacetylation of the respective penta-O-acetyl derivatives (8-10) obtained" by the reaction of aldehyde methyl (or. phenyljhydrazones with the readily available 3,4,5,6,7-penta-O-acetyl-l,Zdideowl-nitro-D-gala&o-hept-l-enitol.

Heating of aqueous solutions of 5-7 severally with an excess of CF,CO,H led to the WyxofuranosyDpyrazole derivatives 11-13, respectively, as a&mixtures or, for 13, a unique product. The furanoid character of 11-13 was shown by the consumption of only 1 mol of periodate, as observed" for the 3-substituted analogues 4. The a&ratios found (NMR data) were 60: 40 for 11 and 65:35 for 12, in agreement with the greater steric hindrance expected for the B-Dlyxofuranosyl than for the cz isomers. Configurations were assigned on the basis of the chemical shifts of the H-l' resonances and the .I,,,,, values. Thus, the 6 values for the H-l' resonances of the (Y isomers 11~ and 12a (4.87 and 4.71 ppm,

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