engleski

FTIR and NMR Spectroscopic Structural Studies of Gentisamide Isolated from Biological Material

Monitoring of drug metabolites is of toxicological, pharmacological and biomedical interest. Nowadays, NMR represents unique and powerful method in detection and quantitative determination of drugs, their metabolites, as well as toxic substances in the urine and other body fluids. However, differentiation of structural related metabolites in biological material could be sometimes very complex. The gentisamide (GAM), the first-pass metabolite of salicylamide (SAM), was studied using FTIR, 1D and 2D homo- and heteronuclear 1H and 13C NMR spectroscopy, and compared with salicylamide, salicylic and gentisic acid. SAM metabolises rapidly to its primary metabolites: SAM-sulphate (SAM-S), SAM-glucuronide (SAM-G) and gentisamide (GAM or SAM-OH), the 5-hydroxylated metabolite. GAM was isolated from urine samples of voluntary examinees, eight hours after ingestion of. salicylamide. Following urine hydrolysis, metabolites were extracted and separated by column chromatography. The chemical structures of isolated metabolites were analysed by means of FTIR, 1H and 13C NMR spectra, and unequivocally confirmed by using chemical and substituent shifts, coupling constants and connectivities in COSY, NOESY, HETCOR and HMBC spectra. From NOESY spectra of GAM we have concluded that amino moiety is oriented toward ortho-proton (at the C-6). Contrary to that, for SAM, theoretical and gas phase data [1, 2] suggested amino group orientation toward ortho-hydroxyl group (at the C-2), due to strong intramolecular hydrogen bonding of the N...HO type. In DMSO-d6 solution we found the same orientation for amino group in SAM, by NMR spectroscopy. On the basis of these findings we have concluded that the presence of additional phenolic group at C-5 in GAM, favorises the formation of the inter- over intramolecular hydrogen bonding. [1] Catalan J, Toriblo F, Acuna A. U. Intramolecular hydrogen bonding and fluorescence of salicylaldehyde, salicylamide, and o-hydroxyacetophenone in gas and condensed phases. J. Phys. Chem. 1982 ; 86:303-6. [2] El-Shahawy S. A. Spectroscopic structural studies of salicylic acid, salicylamide and aspirin. Spectrochim. Acta 1988 ; 44A: 903-7.

FTIR; NMR; Spectroscopy; Biotransformation; Salicylamide; Gentisamide

nije evidentirano