A high-yielding method was developed for the preparation of ingenol 3-angelate (PEP005, ingenol mebutate) via the corresponding 5,20-acetonide without concomitant isomerization of the angelate (Z-form) to the corresponding tiglate (E-form). The general scope of the stereoconservative esterification method was further evaluated on several different alcohols, giving the angelates in up to quantitative yield without isomerization to the tiglate.
Label from [6-14C]-Δ1-piperideine is incorporated nonrandomly into the carbon skeleton of the quinolizidine alkaloid, matrine, in Sophora tetraptera and S. microphylla. The distribution of radioactivity was determined by a new chemical degradation sequence. On the basis of the results, one of two previously postulated biogenetic schemes must be discarded. A modified biogenetic scheme is presented which is consistent with the present results and also leads to the correct stereochemistry of matrine.
A known catabolic pathway of S-methyl-L-methionine in higher plants: donation of a methyl group to L-homocysteine resulting in the production of two molecules of L-methionine, is subjected to stereochemical studies. The two, diastereoisomeric (2-2H, methyl-' 3C)-S-methyl-~-methionines are synthesized and utilised in transmethylation reactions with L-homocysteine as the acceptor and an enzyme preparation from jack beans as a catalyst. The resulting, variously labelled methionine species are converted into butyl esters of the N-trifluoroacetylated derivatives and, as such, subjected to g.1.c. combined with mass spectrometry in two ionisation modes. Experimentally determined parameters such as mass peak intensities, isotopic enrichment factors, diastereoisomeric purities, and protein-derived methionine, are utilised for calculating the stereoselectivity in the enzyme transfer of the diastereoisotopic methyl groups from S-methyl -L-methionine to L-homocysteine. Together, the independent results from the two series of diastereoisomers reveal an enzymic preference of the pro-(R) -* For preliminary accounts of this work,
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