Enantioselective Haloetherification by Asymmetric Opening of meso-Halonium Ions
摘要:
A new approach to enantioselective haloetherification reactions via desymmetrization of in situ-generated meso-halonium ions is described. The combination of N-haloamides as a halogen source and sodium salts of chiral phosphoric acids as catalysts can be used for the cyclization of symmetrical ene-diol substrates, yielding the haloetherification products under practical conditions in enantioenriched form.
Enantioselective Synthesis of 15-Deoxy-Δ<sup>12,14</sup>-Prostaglandin J<sub>2</sub>
作者:Jiaming Li、Brian M. Stoltz、Robert H. Grubbs
DOI:10.1021/acs.orglett.9b04198
日期:2019.12.20
An enantioselectivesynthesis of 15-deoxy-Δ12,14-prostaglandin J2 is reported. The synthesis begins with the preparation of enantiopure 3-oxodicyclopentadiene by a lipase-mediated kinetic resolution. A three-component coupling followed by a retro-Diels-Alder reaction provides the C8 stereochemistry of the prostaglandin skeleton with high enantioselectivity. Stereoretentive olefin metathesis followed
Concise Syntheses of Δ<sup>12</sup>-Prostaglandin J Natural Products via Stereoretentive Metathesis
作者:Jiaming Li、Tonia S. Ahmed、Chen Xu、Brian M. Stoltz、Robert H. Grubbs
DOI:10.1021/jacs.8b12816
日期:2019.1.9
Δ12-Prostaglandin J family is recently discovered and has potent anticancer activity. Concise syntheses of four Δ12-prostaglandin Jnaturalproducts (7-8 steps in the longest linear sequences) are reported, enabled by convergent stereoretentive cross-metathesis. Exceptional control of alkene geometry was achieved through stereoretention.
<i>Z</i>-Selective Ethenolysis with a Ruthenium Metathesis Catalyst: Experiment and Theory
作者:Hiroshi Miyazaki、Myles B. Herbert、Peng Liu、Xiaofei Dong、Xiufang Xu、Benjamin K. Keitz、Thay Ung、Garik Mkrtumyan、K. N. Houk、Robert H. Grubbs
DOI:10.1021/ja4010267
日期:2013.4.17
The Z-selective ethenolysis activity of chelated ruthenium metathesis catalysts was investigated with experiment and theory. A five-membered chelated catalyst that was successfully employed in Z-selective cross metathesis reactions has now been found to be highly active for Z-selective ethenolysis at low ethylene pressures, while tolerating a wide variety of functional groups. This phenomenon also affects its activity in cross metathesis reactions and prohibits crossover reactions of internal olefins via trisubstituted ruthenacyclobutane intermediates. In contrast, a related catalyst containing a six-membered chelated architecture is not active for ethenolysis and seems to react through different pathways more reminiscent of previous generations of ruthenium catalysts. Computational investigations of the effects of substitution on relevant transition states and ruthenacyclobutane intermediates revealed that the differences of activities are attributed to the steric repulsions of the anionic ligand with the chelating groups.
Inhibition of Protein Kinase Cα by Dequalinium Analogues: Dependence on Linker Length and Geometry
作者:Donghui Qin、Regina Sullivan、William F. Berkowitz、Robert Bittman、Susan A. Rotenberg
DOI:10.1021/jm990340z
日期:2000.4.6
Analogues of a bipartite compound, dequalinium (DECA) (quinolinium, 1,1'-(1,10-decanediyl)bis(4-amino-2-methyl diiodide)), were tested for inhibition of protein kinase C alpha (PKC alpha). In vitro assays of monomeric and dimeric analogues support a model in which DECA inhibits PKC alpha by an obligatory two-point contact, a unique mechanism among PKC inhibitors. The presence of unsaturation in the center of the C-10-alkyl linker produced geometric isomers with different inhibitory potencies: cis IC50 = 52 +/- 12 mu M and trans IC50 = 12 +/- 3 mu M, where the trans isomer was equipotent to that of the saturated C-10-DECA. DECA analogues with longer, saturated linkers (C-12, C-14, or C-16) exhibited enhanced inhibitory potencies which reached a plateau with the C-14-linker (IC50 = 2.6 +/- 0.2 mu M) Metastatic melanoma cells treated with 250 nM C-12-, C-14-, or C-16-DECA and irradiated with long-wave UV light (which causes irreversible inhibition of PKC alpha by DECA) confirmed the linker-dependent inhibition of intracellular PKC alpha activity.