Total synthesis of the polyether antibiotic ionomycin
作者:David A. Evans、Robert L. Dow、Thomas L. Shih、James M. Takacs、Robert Zahler
DOI:10.1021/ja00169a042
日期:1990.6
A convergent asymmetric synthesis of the calcium ionophore ionomycin has been achieved through a route that is outlined below. The four illustrated subunits, which comprise the c,-C,,-,, CI)-&r cI&22, and C=-C32 portions of ionomycin,
Rhinacanthus nasutus (L.) KURZ (Acanthaceae) is a shrub widely distributed in South China and India. In this study, the antiproliferative activity of the ethanol extract of root and aqueous extract of leaves of R. nasutus, and the supposed active moiety rhinacanthin C was assessed in vitro using the human cervical carcinoma cell line HeLa, its MDR1-overexpressing subline Hvr100-6, human prostate carcinoma PC-3 cells and human bladder carcinoma T24 cells. Rhinacanthin C was chemically synthesized and its content in the R. nasutus extracts was determined by HPLC with a photodiode array detector. The antiproliferative activity of the R. nasutus extracts was also assessed in vivo using sarcoma 180-bearing mice. It was suggested that 1) the in vitro antiproliferative activity of rhinacanthin C was comparable with or slightly weaker than that of 5-FU, 2) rhinacanthin C showed antiproliferative activity for MDR1-overexpressing Hvr100-6 cells, similarly to parent HeLa cells, 3) the in vitro antiproliferative activity of the ethanol extract of root R. nasutus was due to rhinacanthin C, whereas that of the aqueous extract of leaves of R. nasutus was due to constituents other than rhinacanthin C, and 4) both of the R. nasutus extracts showed in vivo antiproliferative activity after oral administration once daily for 14 d.
Unprecedented stereochemical control in the intramolecular ene-reactions of δ,ε-unsaturated aldehydes using exceptionally bulky organoaluminum reagents: Elucidation of the transition state
作者:Takashi Ooi、Keiji Maruoka、Hisashi Yamamoto
DOI:10.1016/s0040-4020(01)89682-4
日期:——
Unprecedentedstereochemicalcontrol has been achieved in the type II intramolecular ene reactions of δ,ε-unsaturated aldehydes leading to trans-cyclohexanols with excellent selectivity under very mild conditions, using exceptionally bulky methylaluminum bis(4-bromo-2,6-di-tert-butylphenoxide) (MABR). Success of the stereocontrolled cyclization can be ascribable to the ability of this modified organoaluminum
Total Synthesis of (−)-Heptemerone B and (−)-Guanacastepene E
作者:Aubry K. Miller、Chambers C. Hughes、Joshua J. Kennedy-Smith、Stefan N. Gradl、Dirk Trauner
DOI:10.1021/ja0660507
日期:2006.12.1
stereoselective, and convergent totalsynthesis of the unnatural enantiomer of the neodolastane diterpenoid heptemerone B has been completed. Saponification of (-)-heptemerone afforded (-)-guanacastepene E. The absolute stereochemistry of (-)-heptemerone B was thus established as 5-(S), the same as (-)-guanacastepene E. The longest linear sequence of the synthesis comprises 17 (18) steps from simple
新多拉烷二萜类庚烯酮 B 的非天然对映异构体的简洁、立体选择性和收敛全合成已经完成。(-)-庚烯酮皂化得到(-)-胍那卡司汀E。因此,(-)-庚烯酮B的绝对立体化学确定为5-(S),与(-)-胍那卡司酮E相同。最长的线性序列为该合成包括从简单的已知起始材料开始的 17 (18) 个步骤。我们的一般合成方法整合了一系列不同的反应,包括分子内 Heck 反应以创建一个四元立体中心和一个铜酸盐共轭添加以建立另一个。中央七元环通过不常见的电化学氧化闭合,而五元环通过闭环复分解形成。
Initiating radical cyclizations by H transfer from transition metals
作者:John Hartung、Mary E. Pulling、Deborah M. Smith、David X. Yang、Jack R. Norton
DOI:10.1016/j.tet.2008.10.030
日期:2008.12
diphosphine) can be used to initiate radicalcyclizations by transferring H to activated terminal olefins. CpCr(CO)3H can catalyze reductive cyclizations, with H2 as the ultimate reductant. Appropriate substrates can be assembled by the Morita–Baylis–Hillman reaction of methyl acrylate with an aldehyde. Six- as well as five-membered rings can be formed, and a tandem cyclization to decalin can be effected.