Steric and Electronic Effects in Conformational Preferences of C1-Oxygenated Chiral Alkenes
摘要:
A variable temperature NMR study shows that the benzyl protective group on the hydroxy function of a chiral allylic alcohol enhances the CH eclipsed form (I). On the other hand, various silyl ethers enhance the preference for the CO eclipsed conformer. However, when both the allylic R group and the hydroxy protective group are bulky (R tert-butyl, P = TIPS), the staggered conformation of the chiral alkene becomes preferred. An acetate group does not have an apparent effect on the conformational preference of the protected allylic alcohol. These facts are explained in terms of steric and electronic interactions.
Synthetic studies of didemnins. i. revision of the stereochemistry of the hydroxyisovalerylpropionyl (hip) unit.
作者:William R. Ewing、Krishna L. Bhat、Madeleine M. Joullie
DOI:10.1016/s0040-4020(01)96067-3
日期:——
Synthetic and spectral evidence for the absolute configuration of the asymmetric centers of the hydroxyisovalerylpropionyl (HIP) unit present in the depsipeptides didemnins is discussed.
合成和光谱证据的绝对构型中存在于二肽双氢精蛋白中的羟基异戊二酰基丙酰基(HIP)单元的不对称中心。
Access to Functionalized Steroid Side Chains via Modified Julia Olefination
作者:Enver Cagri Izgu、Aaron C. Burns、Thomas R. Hoye
DOI:10.1021/ol102936z
日期:2011.2.18
Various functionalizedsteroidalsidechains were conveniently accessed by a modified Julia olefination strategy using a common sulfone donor and an appropriate α-branched aldehyde acceptor. For the coupling of these hindered classes of reaction partners (and in contrast to typically observed trends), the benzothiazolyl(BT)-sulfone anion gave superior outcomes compared to the phenyltetrazolyl(PT)-sulfone
使用常见的砜供体和合适的α-支化醛受体,通过改进的 Julia 烯化策略可以方便地获得各种功能化的甾体侧链。对于这些受阻类别的反应伙伴的偶联(并且与通常观察到的趋势相反),与苯基四唑基 (PT)-砜阴离子相比,苯并噻唑基 (BT)-砜阴离子具有更好的结果。
Synthesis of 26,27-bisnorcastasterone analogs and analysis of conformation–activity relationship for brassinolide-like activity
Three castasterone (CS) derivatives with varied side-chain moieties, 26,27-bisnorcastasterone (20S-bisilorCS), 20-epi-26,27-bisnorcastastcrone (20R-bisnorCS), and 21,26,27-trisnorcastasterone (trisnorCS), were synthesized stereoselectively from either stigmasterol or dehydroisoandrosterone. The 50% effective doses (ED50, nmol/plant) in the concentration-response Curve for brassinolide-like activity in the rice lamina inclination assay were determined to be 0.020 nmol (pED(50) = 10.7) for 20S-bisnorCS, 3.2 nmol (pED50 = 8.5) for 20R-bisnorCS, and 2.0 nmol (pED50 = 8.7) for trisnorCS. An analog containing an ester linkage between the steroid and the side-chain moiety of 20S-bisnorCS was also synthesized and its activity was evaluated to be 3.2 nmol (pED50 = 8.5), being equipotent to 20R-bisnorCS and trisnorCS. The activity of 20S-bisnorCS was 1/40 that of CS. The conformation analysis was conducted using a systematic search, showing that the activity decreases with an increase in the degree of freedom of the side chain of the steroidal skeleton. (c) 2005 Elsevier Ltd. All rights reserved.
KO, KWANG-YOUN;FRAZEE, W. J.;ELIEL, E. L., TETRAHEDRON, 1984, 40, N 8, 1333-1343