Studies on the Conformation of Polyhydroxyalkylpyrazolo (3,4-b) Quinoxalines

Synthesis of new 1,3,4-thiadiazole and 1,2,3,4-oxathiadiazole derivatives from carbohydrate precursors and study of their effect on tyrosinase enzyme

5-(1,2,3,4-Tetrahydroxybutyl)-2-methylfuran-3-carbohydrazide (2) was condensed with a variety of ketones to afford carbohydrazide derivatives 3-6. Acetylation of 3-5 afforded the acetyl derivatives 7-9, while periodate oxidation of 3-6 afforded the formyl derivatives 10-13. Acid catalyzed condensation of thiosemicarbazide or o-tolylthiosemicarbazide with the prepared aldehydes 10-12 gave thiosemicarbazone derivatives 14-19. Cyclization of the latter with acetic anhydride afforded 4,5-dihydro-1,3,4-thiadiazolyl derivatives 20-25. On the other hand, condensation of p-tosylhydrazine with the prepared aldehydes 10-12 afforded p-tosylhydrazone derivatives 26-28. Cyclization of 26-28 with acetic anhydride afforded 1,2,3,4-oxathiadiazole derivatives 29-31 respectively. Moreover, the obtained results regarding to the effect of some of the prepared compounds on tyrosinase enzyme showed that the majority of these compounds having an inhibitory effect; especially compounds 12, 16, 17, and 28.

Synthesis and 1H NMR studies of 3-(D-erythro-glycerol-1-yl)-1H-pyrazolo[3,4-b]quinoxaline and its 7-chloro and 7-methyl analogues

3-(D-erythro-Glycerol-1-yl)-1H-pyrazolo[3,4-b]quinoxaline and its 7-chloro and 7-methyl analogues (11 and 12) were prepared from the corresponding quinoxalines. The 7-substituted analogues 11 and 12 were obtained as the preponderant isomers, and the 6-substituted analogues as the minor isomers. The structure and position of the substituent were determined by 1H NMR studies. The effect of substitution on the chemical shift of other protons is discussed.