The geometry of N-hydroxymethyl compounds. Part 4. Studies on ground-state geometry and decomposition of N-(hydroxymethyl)triazenes using MNDO calculations and kinetic studies

Abstract

MNDO calculations of the most favoured conformations of antitumour 3-(hydroxymethyl)-3-methyl-1-(4-X-phenyl)triazenes (2) indicate N–CH₂OH bond lengths of over 1.49 Å(lengthened by electron-withdrawing groups), correlated with high lability under physiological conditions (t_1/2 under 1 s). Hydrolysis rates of 2o(X = NO₂) in methanol/acetonitrile containing water were determined using high performance liquid chromatography (HPLC) and extrapolated to give a t_1/2 of 43 s at 100% water. Modelling of decomposition pathways of 2d(X = CH₃) using MNDO predicts that concerted loss of formaldehyde is not favoured. Loss of [H₂COH]⁺ from nitrogen protonated 2d is also a high energy process, but loss of formaldehyde from deprotonated 2d seems feasible under basic conditions. Under, acidic conditions the energetically preferred process is loss of water from protonated 2d to give an iminium ion, even though the required initial O-protonation is disfavoured over protonation on nitrogen.