Análisis de los productos de las fotólisis del ácido fólico en medio alcalino separados por TLC.

GUSTAVO SUÁREZ; FRANCO M. CABRERIZO; ANDRES H. THOMAS; FERNANDO S. GARCÍA EINSCHLAG; MARIO FELIZ; ALBERTO L. CAPPARELLI

La Plata, Argentina

Congreso; XXII CONGRESO ARGENTINO DE QUIMICA; 1998

The photolysis of folic acid (_N-(4-{[(2-amino-1,4-dihydro-4-oxopteridin-6-yl)methyl]amino}benzoyl)-_- glutamic acid) in alkaline aqueous solution (pH 10.0 ± 11.0) was carried out at 350 nm at room temperature and monitored by UV/VIS spectrophotometry, anal. and prep. thin-layer chromatography (TLC), and highperformance liquid chromatography (HPLC, HPLC/MS). The folate species underwent at least two independent photo-oxidation pathways, which were not observed when the acid form was photolyzed at pH_7. The presence of O2 was essential in these oxidation pathways. Evidence for the role of singlet oxygen was established. In one of the pathways, the folate underwent cleavage, yielding 6-formylpterin (_2-amino-1,4- dihydro-4-oxopteridine-6-carboxaldehyde) and (4-aminobenzoyl)glutamic acid as photoproducts. The other pathway yielded a new photostable product A of molecular mass 455, which could be isolated and stored in acidic or neutral aqueous solution. However, A was rather unstable in alkaline media undergoing a thermal reaction to a product B of lower molecular mass (427). The kinetics of this thermal reaction was analyzed with a stopped-flow spectrophotometer. A linear dependence of the first-order rate constant with the OH_ concentration was observed. The corresponding bimolecular rate constant was 1.1 __1 s_1. The quantum yields of substrate consumption and of photoproduct formation were determined. The here-reported photochemical behavior of folate solutions departs from results in acid media, where phototransformation proceeded via the cleavage of the acid form into 6-formylpterin and (4-aminobenzoyl)glutamic acid as the first major photoproducts, and where no thermal reactions were observed.