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Acyclic purine nucleoside analogues: computational and NMR studies of conformational behaviour

The conformational space of N-7- and N-9-(2-hydroxypropyl)-6-(N-pyrrolyl)purine as well as of N-7- and N-9-(2, 3-dihydroxypropyl)-6-(N-pyrrolyl)purine has been studied by molecular mechanics (MMX force field) and semiempirical (PM3) calculations. Eight local minima were obtained for the N-7-(2-hydroxypropyl) regioisomer by the MMX force field and reoptimised by the PM3 method to locate the global minimum. The conformation of the N-7-(2, 3-dihydroxypropyl) regioisomer is locked by intramolecular H-bonding and therefore more rigid. The results of theoretical calculations are in agreement with H-1 and C-13 NMR analysis of substituent chemical shifts, C-H and H-H coupling constants and connectivities in 2D homo- and heteronuclear correlation spectra.

acyclic purine nucleosides ; conformation ; MMX ; PM3 ; H-1 and C-13 NMR

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