For the first time, intramolecular allylic amination was conducted using rhodium(III) according to an "inner-sphere" type mechanism with amines activated by only one electron-withdrawing group. The activation of C(sp(3))-H bonds was chemoselective and allows the access to a variety of substituted cyclic amines such as pyrrolidines and piperidines.
Structure–activity relationships in the conversion of vitamin K analogues into menaquinone-4. Substrates essential to the synthesis of menaquinone-4 in cultured human cell lines
To reveal an essential biological role of menaquinone-4, we have clarified that dietary PK was converted to menaquinone-4 (MK-4) in animal tissues using deuterated vitamin K analogues. However, the kinds of analogue converted into MK-4 have not been elucidated. In this study, we examined structure-activity relationships in the conversion of several vitamin K analogues, with a substituted side chain, into MK-4 using cultured human cell lines. The results differed with the side chain of the analogues, that is, (1) the length of the isoprene unit and (2) the number of double bonds in the side chain. These findings would be useful for clarifying the mechanism of conversion of other vitamin K homologs into MK-4 as well as related enzymes. (c) 2010 Elsevier Ltd. All rights reserved.
Trichodiene Synthase. Stereochemical Studies of the Cryptic Allylic Diphosphate Isomerase Activity Using an Anomalous Substrate
作者:David E. Cane、Guohan Yang
DOI:10.1021/jo00098a046
日期:1994.9
Incubation of (7S)-6,7-dihydrofarnesyl diphosphate with trichodiene synthase gave, as previously described, a mixture consisting of 80% dihydrofarnesene isomers 6-8 accompanied by 6% trans- 6,7-dihydrofarnesol (10) and 13% 6,7-dihydronerolidol (9). The latter product has now been shown to be (3S,7S)-6,7-dihydronerolidol [(3S,7S)-9] by direct comparison with synthetic (3S,7S)-6,7-dihydronerolidol and (3RS,7S)-6,7-dihydronerolidol using chiral capillary gas chromatography. The observed formation of (3S,7S)-9 can be accounted for by backside attack of water on an allylic cation-pyrophosphate anion pair generated by syn allylic rearrangement of dihydrofarnesyl diphosphate (5) and ionization of the resulting (3R,7S)-6,7-dihydronerolidyl diphosphate (14). These results provide further support for the proposed isomerization of farnesyl diphosphate (1) to (3R)-nerolidyl diphosphate (3) in the enzymatic formation trichodiene (2).