Synthesis of specifically 2 H‐labeled reserpines, 3,4,5‐trimethoxybenzoic acids, and syringic acid

3,4,5‐Trimethoxy‐ 2 H 9 ‐, 4‐methoxy‐3,5‐dimethoxy‐ 2 H 6 ‐, and 4‐hydroxy‐3,5‐dimethoxy‐ 2 H 6 ‐benzoic acids were prepared from n ‐propyl 3,4,5‐trihydroxybenzoate ( n ‐propyl gallate) by means of appropriate alkylation‐hydrolysis sequences employing iodomethane‐ 2 H 3 or dimethyl‐ 2 H 6 ‐sulfate as the deuterium source. 4‐Methoxy‐ 2 H 3 ‐3,5‐dimethoxybenzoic acid was similarly prepared from ethyl 4‐hydroxy‐3,5‐dimethoxybenzoate. The labeled trimethoxybenzoic acids were converted to the corresponding 2 H‐labeled reserpines by condensation of the acid chlorides with methyl reserpate in pyridine according to the classical procedure. The labeled reserpine analog methyl 18‐O‐(4‐hydroxy‐3,5‐dimethoxy‐ 2 H 6 )benzoyl reserpate was likewise prepared from 4‐hydroxy‐3,5‐dimethoxy‐ 2 H 6 ‐benzoic acid via the intermediate methyl 18‐O‐(4‐ethoxycarbonyloxy‐3,5‐dimethoxy‐ 2 H 6 ‐benzoyl)reserpate (syrosingopine‐ 2 H 6 ). The isotopic purity of each compound exceeded 99 atom percent 2 H.