Trimethylsilylation of biogenic indoleamines : Practical Kinetic and analytical aspects related to tryptamine and 5-hydroxytryptamine

Abstract

An attempt is made to answer some practical kinetic and identification questions on the trimethylsilylated (TMS) derivatives of tryptamine (T) and 5-hydroxytryptamine (5HT). Considering the theoretically possible five and 11 TMS derivatives of T and 5HT, respectively, a gas chromatographic—mass spectrometric study of these reaction profiles established the identification of the five T derivatives and all of the six 5HT derivatives whose formation was considered kinetically feasible. Reaction parameters must be optimized to avoid a multiplicity of TMS derivatives in practical applications. A kinetic approach using different catalysts (trimethylsilylimidazole, trimethylchlorosilane, pyridine) indicates that the ease of silylation would follow the order O 5 > 1st N∞ position > N 1 2nd N∞ position. The best results were obtained by reaction with a N,O-bis(trimethylsilyl)trifluoroacetamide—trimethylsilylimidazolepyridine mixture at 70° for 60 min, which enhances the formation of the fully silylated derivatives. The relative merits of the silyl versus the acyl derivatives of these amines are discussed in relation to practical applications.