Synthesis of some furoic and thenoic esters of the methyl D-glucopyranosides, and their stability to high-energy radiation

The esters obtained by complete esterificatlon of methyl D-glucopyranosides with, respectively, 2-furoyl chloride (β-, 1: α-, 2), 2-furanacryloyl chloride (β-, 3: α-, 4) 5-bromo-2-furoyl chloride (β-, 5: α-, 6) 2-thenoyl chloride (β-, 7: α-, 8) 5-methyl-2-thenoyl chloride (β-, 9: α-, 10) 5-bromothiopheneacryloyl chloride (β-, 11: α-, 12) and 2-thiopheneacryloyl chloride (β-, 13: α-, 14) were subjected to irradiation (2.8 x 1019 eV/gh) in the solid state to a dosage of 7.1 x 1020 eV/g. The e.s.r. spectra of irradiated (irr.) methyl α- and β-d-D-glucopyranoside and irr. esters 1-14 were examined to determine the nature of the radiation damage: those of the unsubstituted d-glucopyranosides contain one very strong doublet and one very strong singlet, indicating that cleavage of the C-I-O bond (doublet) and dehydrogenation of the C-I-H bond (singlet) had occurred. The e.s.r. spectra of irr. furoates 1 and 2 contain strong doublets. but those of 3-6 have none, showing that the glycosidic bonds in the latter are highly stable to radiation damage, but those in 1 and 2 are stable compared to that in methyl α-d-glucopyranoside. The e.s.r. spectra of the irr. thenoic esters indicated that glycosidic bonds to 11 and 12 are highly stable to radiation initiated cleavage (absence of doublets), those in 7-10 are fairly stable (weak doublets), and those in 13 and 14 are more stable (strong doublets) than that in methyl α-d-glucopyranoside (very strong doublet) Radiation-initiated, dehydrogenation reactions were decreased for 7 and 8 (very weak singlets), 9 and 10 (very weak, and weak singlets), and 11 and 12 (strong singlets). compared with those of methyl α-d-glucopyranoside, 13, and 14 (very strong singlets). The radiation stability of these esters may arise from intramolecular transfer of energy to the ester groups, and be followed by dissipation of the energy. The anomeric form of methyl d-glucopyranoside has no influence on the localization of the energy.