PdCl2L2-type complexes with phosphines (L = PPhx(C6F5)3-x (x = 0-3)), phosphites (L = P(OMe)3, P(OPh)3, P(OEt)3), and phosphinites (L = PPh2(OC6F5), PPh2(O-3,5-F2C6H3), PPh2(OEt), PPh2(O-n-Bu), PPh2(O-t-Bu)) were synthesized and characterized by UV-vis and 31P NMR methods. PdCl2L2 complexes with less sterically demanding phosphines (Θ < 140°) exist as cis isomers, which is confirmed by the X-ray structure of cis-PdCl2[PPh2(OEt)]2. These complexes react with CO in the presence of NEt3 forming Pd(CO)xLy (x + y = 4) type carbonyls characterized by IR spectra. All PdCl2L2 complexes studied are active as precursors of benzyl bromide carbonylation catalysts at 40°C and 1 atm CO; however, the activity of the cis isomers is higher than that of the trans isomers. The highest yields of the carbonylation product, phenylacetic acid methyl ester, were obtained using cis-PdCl2[P(OMe)3]2 (92%), cis-PdCl2[P(OPh)3]2 (89%), and cis-PdCl2[PPh2(O-n-Bu)]2 (78%) as catalyst precursors.Key words: palladium complexes, fluorinated phosphines, benzyl bromide carbonylation.
Type II thioesterases (TE IIs) were shown to maintain the efficiency of polyketide synthases (PKSs) by removing acyl residues blocking extension modules. However, the substrate specificity and kinetic parameters of these enzymes differ, which may have significant consequences when they are included in engineered hybrid systems for the production of novel compounds. Here we show that thioesterase ScoT associated with polyketide synthase Cpk from Streptomyces coelicolor A3(2) is able to hydrolyze acetyl, propionyl, and butyryl residues, which is consistent with its editing function. This enzyme clearly prefers propionate, in contrast to the TE IIs tested previously, and this indicates that it may have a role in control of the starter unit. We also determined activities of ScoT mutants and concluded that this enzyme is an ␣/ hydrolase with Ser90 and His224 in its active site.
The new phosphinite and phosphonite complexes (1-8) are very efficient catalysts for the methoxycarbonylation of iodobenzene and Heck cross-coupling of bromobenzene with butyl acrylate. High catalytic activity of these complexes can be explained by their in situ transformations during the reaction, stimulated by the presence of water, acid (HCl) or base (NEt(3)). Hydrolysis of phosphinite palladium complexes of the form trans-PdCl(2)[PPh(2)(OR)](2) (R = C(6)F(5), 2, (t)Bu 3, or O-menthyl 4) results in the formation of the dimeric complex [mu-ClPd(PPh(2)OH)(PPh(2)O)](2) 5, which is deprotonated by NEt(3), producing a polymeric complex of formula [Pd(P(O)PPh(2))(2)](n) 8. The reverse reaction, protonolysis of 8 with HCl, leads back to 5 and the monomeric complex 5a. The phosphinite complex PdCl(2)[PPh(2)(OBu)](2)1 with a more lipophilic ligand, PPh(2)(OBu), does not undergo hydrolysis under the same conditions. In the reaction of PdCl(2)(cod) with P(OPh)(2)(OH), the new dimer [mu-ClPd(P(OPh)(2)OH)(P(OPh)(2)O)](2) 6 was obtained, whereas reaction of Pd(OAc)(2) with P(OPh)(2)(OH) leads to the polymeric complex [Pd[P(O)(OPh)(2)](2)](n) 7. Protonolysis of 7 with HCl results in the formation of 6.
Superpotent and highly delta-opioid receptor selective cyclic peptides of the general formula H-Tyr-c[D-Pen-Gly-Phe(p-X)-Pen]-Phe-OH (where X = hydrogen or halogen) have been synthesized. In the binding assays the most selective and most potent compound is the p-bromophenyl-alanine-4 analogue (IC50 value = 0.19 nM, selectivity ratio = 21,000 for delta vs mu). In the GPI and MVD bioassays the most selective and most potent analogue is the p-fluoro-substituted analogue Tyr-[D-Pen-Gly-Phe(p-F)-Pen]-Phe-OH. In the MVD assay it has an exceptionally low IC50 value of 0.016 nM and a delta vs mu selectivity ratio of 45,000.
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