Artefactual pyruvate and 2-oxobutyrate produced by trimethylsilylation of methylmalonic and ethylmalonic acids in the presence of oxygen
Trimethylsilylation of methylmalonic and ethylmalonic acids in the presence of headspace atmospheric oxygen is shown to produce the trimethylsilyl derivatives of pyruvic and 2-oxobutyric acids, along with 2-hydroxy-2-methylmalonic and 2-hydroxy-2-ethylmalonic acids, respectively. This may lead to overestimation of these keto acids, if they were not oximated in the original sample, and the mistaken reporting of the 2-hydroxymalonates.
Trimethylsilylation of malonate ester enols.
Malonic acid silylates readily to yield the expected bis-trimethylsilyl (TMS) ester; this ester reacts further in the silylating mixture to yield a tris-TMS derivative, apparently through enolization of one of the ester groups. Methylmalonic and hydroxymalonic acids behave similarly. The methyl and ethyl esters of malonic acid also silylate once with some facility. Mass spectra of these derivatives are presented
Phloroglucinol derivatives from Hypericum japonicum.
The isolation and identification of a new phloroglucinol derivative (2), a diterpenol (4), together with the known compounds flavesone (1) and sarothralen B (3), from the aerial parts of Hypericum japonicum are reported. Their structures were established by extensive spectral analysis and the structure of (3) has also been confirmed by a single crystal X-ray determination.