The rhodium(I)-catalyzed conjugate addition
of aryl- or 1-alkenylboronic acids to enones was carried
out in high yields at 50 °C in an aqueous solvent.
A
combination of (acac)Rh(CO)2 and dppb was
recognized
to be highly effective for the addition to acyclic and
cyclic
enones.
CRKI (SH2-SH3) and CRKII (SH2-SH3-SH3) are splicing isoforms of the oncoprotein CRK that regulate transcription and cytoskeletal reorganization for cell growth and motility by linking tyrosine kinases to small G proteins. CRKI shows substantial transforming activity, whereas the activity of CRKII is low, and phosphorylated CRKII has no biological activity whatsoever. The molecular mechanisms underlying the distinct biological activities of the CRK proteins remain elusive. We determined the solution structures of CRKI, CRKII and phosphorylated CRKII by NMR and identified the molecular mechanism that gives rise to their activities. Results from mutational analysis using rodent 3Y1 fibroblasts were consistent with those from the structural studies. Together, these data suggest that the linker region modulates the binding of CRKII to its targets, thus regulating cell growth and motility.
The cross-coupling reaction of arylboronic acid with chloroarenes to give biaryls was carried out in high yields at 70-80 degrees C in the presence of a nickel(0) catalyst and K(3)PO(4) (3 equiv) in dioxane or benzene. The nickel(0) catalyst in situ prepared from NiCl(2).L (L = dppf, 2PPh(3)) (3-10 mol %) and 4 equiv of BuLi at room temperature was recognized to be most effective. The reaction can be applicable to a wide range of chloroarenes having an electron-withdrawing or an electron-donating group such as 4-NC, 4-CHO, 2- or 4-CO(2)Me, 4-COMe, 4-NHAc, 4-Me, 4-OMe, 4-NH(2), and 4-NMe(2). The Hammett's plot of the substituent effect of chloroarenes revealed that the reaction involves a rate-determining oxidative addition of chloroarenes to the nickel(0) complex.
Highly inert to ionic additions to aldehydes, aryl- and 1-alkenylboronic acids succumb to a catalytic variant mediated by a [Rh(acac)(CO) ]-diphosphane complex in aqueous phase at 80-95°C to yield secondary alcohols [Eq. (a)]. A key step in the catalytic cycle is the transmetalation between the boron reagent and the rhodium complex. L =diphosphane (e.g. 1,1'-bis(diphenylphosphanyl)ferrocene); R=aryl, 1-alkenyl; R'=alkyl, aryl; acac=acetylacetonate.
Norzoanthamine, an alkaloid isolated from Zoanthus sp., can suppress the loss of bone weight and strength in ovariectomized mice. Norzoanthamine derivatives can also strongly inhibit the growth of P-388 murine leukemia cell lines and human platelet aggregation. However, norzoanthamine's densely functionalized complex stereostructure and scarce availability from natural sources have proved a synthetic challenge. We report the stereoselective total synthesis of norzoanthamine in 41 steps, with an overall yield of 3.5% (an average of 92% yield each step).
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