Powerful Ti-crossed Claisen condensation between ketene silyl acetals or thioacetals and acid chlorides or acids

[Structure: see text] A powerful Ti-crossed Claisen condensation between ketene silyl acetals (KSAs) and acid chlorides was successfully performed to give alpha-monoalkylated esters and thermodynamically unfavorable (less accessible) alpha,alpha-dialkylated beta-keto esters in good yield (46 examples; 41-98% yield). A closely related reaction between ketene silyl thioacetals (KSTAs) and acid chlorides also proceeded smoothly to give alpha-monoalkylated and alpha,alpha-dialkylated beta-keto thioesters (21 examples; 61-97% yield). The present protocol was extended to the direct condensation of KSAs with carboxylic acids (14 examples; 71-97% yield).     

NaOH-catalyzed crossed Claisen condensation between ketene silyl acetals and methyl esters

We have developed a practical crossed Claisen condensation between ketene silyl acetals and methyl esters using catalytic NaOH to obtain alpha-monoalkylated beta-keto esters and inaccessible alpha,alpha-dialkylated beta-keto esters.     

Practical synthesis of optically active alpha,alpha-disubstituted malonamic acids through asymmetric hydrolysis of malonamide derivatives with Rhodococcus sp. CGMCC 0497

A variety of alpha,alpha-disubstituted malonamides undergo enantioselective hydrolysis with Rhodococcus sp. CGMCC 0497 to give challenging enantiopure alpha,alpha-disubstituted malonamic acids with up to >99% enantiomeric excesses and 98% chemical yields. The enantioselectivity originated from the effects of a highly enantioselective amidase. The products could be converted to valuable (R)- or (S)-alpha,alpha-dialkylated amino acids after routine conversions.     

Stereocontrolled formation of amino acids and N-heterocycles bearing a quaternary chiral carbon

[STRUCTURE: SEE TEXT] Stereocontrolled formation of tertiary or quaternary chiral carbons bearing nitrogen was achieved using the [3,3]-sigmatropic rearrangement of cyanate to isocyanate as a key element. A short and highly selective sequence of reactions, starting from p-menthane-3-carboxaldehyde, was developed leading to alpha,alpha-dialkylated alpha-amino acids or N-heterocycles, depending on the method of cleavage of the auxiliary.     

An Efficient Strategy to Orthogonally Protected (R)- and (S)-alpha-Methyl(alkyl)serine-Containing Peptides via a Novel Azlactone/Oxazoline Interconversion Reaction

A novel strategy for the synthesis of (R)- and (S)-alpha-methyl(alkyl)serine-containing peptides is presented. Using (S)-phenylalanine cyclohexylamide 6 as chiral auxiliary, the optically pure azlactones (R)- and (S)-2 were synthesized via a novel azlactone/oxazoline interconversion reaction (Figures 3 and 6). These azlactones constitute fully protected and activated synthetic equivalents of (R)- and (S)-alpha-methylserine and can be directly incorporated into peptides without further protective group manipulations. Like other alpha,alpha-dialkylated glycines, optically pure alpha-alkylserines can be used to stabilize beta-turn and alpha-helical conformations in short peptides.     

A ruthenium-grafted hydrotalcite as a multifunctional catalyst for direct alpha-alkylation of nitriles with primary alcohols

Treatment of a hydrotacite, Mg6Al2(OH)16CO3, with an aqueous solution of RuCl3.nH2O afforded a monomeric Ru(IV) species on the surface of the hydrotalcite. This novel Ru-grafted hydrotalcite (Ru/HT) efficiently catalyzed alpha-alkylation of nitriles with primary alcohols through the cooperative catalysis between the Ru species and the surface base sites. The catalyst system could be further extended for the one-pot synthesis of alpha,alpha-dialkylated phenylacetonitriles via the base-catalyzed Michael reaction of alpha-alkylated phenylacetonitrile with activate olefins.     

Mild and efficient pentafluorophenylammonium triflate (PFPAT)-catalyzed C-acylations of enol silyl ethers or ketene silyl (Thio)acetals with acid chlorides

A pentafluorophenylammonium triflate (PFPAT) catalyst (5 mol %) successfully promoted C-acylation of enol silyl ethers with acid chloride to produce various beta-diketones (12 examples; 62-92% yield). Similarly, C-acylation of ketene silyl acetals or ketene silyl thioacetals (i.e., crossed Claisen condensation) proceeded smoothly to provide not only alpha-monoalkylated beta-keto (thio)esters but also thermodynamically unfavorable (less accessible) alpha,alpha-dialkylated beta-keto (thio)esters in good to excellent yield (38 examples; 60-92% yield).     

Intrinsic conformational characteristics of alpha,alpha-diphenylglycine

Quantum mechanical calculations at the B3LYP/6-31+G(d,p) level have been used to investigate the intrinsic conformational preferences of alpha,alpha-diphenylglycine, a simple alpha,alpha-dialkylated amino acid bearing two phenyl substituents on the alpha-carbon, in both the gas phase and aqueous solution. Nine minimum energy conformations have been characterized for the N-acetyl-N'-methylamide derivative within a relative energy range of about 9 kcal/mol. The relative stability of these structures is largely influenced by specific backbone...side chain and side chain...side chain interactions that can be attractive (N-H...pi and C-H...pi) or repulsive (C=O...pi). On the other hand, comparison with the minimum energy conformations calculated for alpha-aminoisobutyric acid, in which the two phenyl substituents are replaced by methyl groups, revealed that the bulky aromatic rings of alpha,alpha-diphenylglycine induce strain in the internal geometry of the peptide. Finally, a set of force-field parameters for classical Molecular Mechanics calculations was developed for the investigated amino acid. Molecular Dynamics simulations in aqueous solutions have been carried out to validate the parameters obtained.     

Intrinsic conformational preferences of C(alpha,alpha)-dibenzylglycine

The intrinsic conformational preferences of C (alpha,alpha)-dibenzylglycine, a symmetric alpha,alpha-dialkylated amino acid bearing two benzyl substituents on the alpha-carbon atom, have been determined using quantum chemical calculations at the B3LYP/6-31+G(d,p) level. A total of 46 minimum energy conformations were found for the N-acetyl- N'-methylamide derivative, even though only nine of them showed a relative energy lower than 5.0 kcal/mol. The latter involves C 7, C 5, and alpha' backbone conformations stabilized by intramolecular hydrogen bonds and/or N-H...pi interactions. Calculation of the conformational free energies in different environments (gas-phase, carbon tetrachloride, chloroform, methanol, and water solutions) indicates that four different minima (two C 5 and two C 7) are energetically accessible at room temperature in the gas phase, while in methanol and aqueous solutions one such minimum (C 5) becomes the only significant conformation. Comparison with results recently reported for C (alpha,alpha)-diphenylglycine indicates that substitution of phenyl side groups by benzyl enhances the conformational flexibility leading to (i) a reduction of the strain of the peptide backbone and (ii) alleviating the repulsive interactions between the pi electron density of the phenyl groups and the lone pairs of the carbonyl oxygen atoms.     

Improved separation of alpha chains of collagen type I, type III, and type V by noninterrupted electrophoresis using thioglycolic acid as a negatively charged reducer

Improved separation of alpha chains of collagen type I (alpha 1 [I]2 alpha 2[I]), type III(alpha 1[III]3), and type V (alpha 1[V]alpha 3[V])was achieved by noninterrupted sodium dodecyl sulfate-polyacrylamide gel electrophoresis with a negatively charged reducer, thioglycolic acid. The thioglycolic acid, added to the running buffer of the cathodic reservoir, in the middle of electrophoresis quickly migrated in the gel anode, reducing interchain disulfide linkages in collagen type III and dissociating it into its alpha chain monomer, alpha 1[III], without an interruption of electrophoresis. The alpha chain, alpha 1[III], migrated more slowly than the alpha 1 [I] and alpha 2[I] chains of collagen type I, resulting in an excellent separation of alpha 1[III] from alpha 1[I]. The mobility of alpha 1[III] could be controlled by varying the time of thioglycolic acid addition to the running buffer. This enabled us not only to separate alpha 1[III] from alpha 1[I] and alpha 1[V], but also to precisely quantitate these alpha chains, even at low protein loading of mixed samples.     

Synthesis of PDK, a novel porphyrin-linked dicarboxylate ligand

A novel trinucleating ligand system H4(PDK), for porphyrin-based diamine bis(Kemp's triacid)imide, was constructed by using two molecules of Kemp's triacid and one molecule of porphyrin as building blocks. The dimeso-substituted octaalkylporphyrin unit, carrying bromomethyl groups at the ortho positions of two trans-positioned meso-phenyl groups, was synthesized from (3,3'-diethyl-4,4'-dimethyl-2,2'-dipyrrolyl)methane and (alpha-bromo-o-tolualdehyde. The structures of both of the two atropisomers (alpha,alpha- and alpha,beta-) of bromoporphyrin, H2(alpha,alpha-BP) and H2(alpha,beta-BP), were determined by X-ray crystallography, with the alpha,beta-isomer as the free base form and the alpha,alpha-isomer as the zinc complex. Both the alpha,alpha- and alpha,beta-isomers of the bromomethyl porphyrins were converted to their aminomethyl derivatives, H2(alpha,alpha-AP) and H2(alpha,beta-AP), through the corresponding imidoporphyrin intermediates, H2(alpha,alpha-IP) and H2(alpha,beta-IP), by the Gabriel synthesis. The alpha,alpha- and alpha,beta-aminoporphyrins were coupled with Kemp's triacid anhydride-chloride to form H4(alpha,alpha-PDK) and H4(alpha,beta-PDK), respectively. Unlike the alpha,beta-isomer, the structure of which was determined by X-ray crystallography for the zinc complex, H4(alpha,alpha-PDK) has a remarkable and complicated solvent-dependent 1H NMR spectrum that suggests the existence of hydrogen bonding interactions between two convergent, tethered Kemp's triacid units, as predicted in a modeling study. The convergent feature is essential for the target ligand H4(alpha,alpha-PDK) to form trinuclear metal complexes with a bis(carboxylato) dimetallic unit sitting above a metalloporphyrin ring.     

Molecular identification of Ca2+ channels in human sperm

The acrosome reaction is a Ca(2+)-dependent exocytotic process that is a prerequisite step for fertilization. External calcium entry through voltage-activated Ca(2+) channels is known to be essential in inducing the acrosome reaction of mammalian spermatozoa. Due to their complex geometry, however, electrophysiological identification of sperm Ca(2+) channels has been limited. Here we identified Ca(2+) channel mRNAs expressed in motile human sperm using RT-PCR and their levels were compared using RNase protection assays. L-type, non- L-type, and T-type Ca(2+) channel mRNAs were detected by RT-PCR using degenerate primers. Cloning and sequencing of the PCR products revealed alpha1B, alpha1C, alpha1E, alpha1G, and alpha1H sequences. RT-PCR using specific primers repeatedly detected alpha1B, alpha1C, alpha1E, alpha1G, and alpha1H mRNAs, and additionally alpha1I mRNA. But alpha1A and alpha1D messages were not detected. Relative expression levels of the detected Ca(2+) channel subtypes were compared by RNase protection assays. The abundance of detected mRNA messages was in the following order: alpha1H alpha1G alpha1E alpha1B alpha1C alpha1I. These findings indicated that human motile sperm express multiple voltage-activated Ca(2+) channel RNAs among which T-type and non-L-type channel messages are likely to be predominantly expressed. Based on their relative expression levels, we propose that not only T-type but also non-L-type calcium channels may be major gates for the external calcium influx, required for the acrosome reaction.     

Synthesis of 6-hydroxylated bile acids and identification of 3 alpha,6 alpha,7 alpha,12 alpha-tetrahydroxy-5 beta-cholan-24-oic acid in human meconium and neonatal urine

Three 6-hydroxylated bile acids, 3 alpha,6 alpha,7 alpha,12 alpha-, 3 alpha,6 beta,7 alpha,12 alpha- and 3 alpha,6 beta,7 beta,12 alpha-tetrahydroxy-5 beta-cholan-24-oic acids, were synthesized from methyl cholate, and a sensitive method was developed for analyzing them by gas chromatography-mass spectrometry for the stoichiometric study of fetal bile acids. 3 alpha,6 alpha,7 alpha,12 alpha-Tetrahydroxy-5 beta-cholan-24-oic acid (6 alpha-hydroxylated cholic acid) was identified from human meconium and healthy neonatal urine by comparison with the mass spectrum of the reference compound. In human meconium, 6 alpha-hydroxylated cholic and chenodeoxycholic acids were determined in 1.2% and 29.0% of the total bile acids, respectively. We discuss the significance of hydroxylation at the C-1 beta and C-6 alpha positions of bile acids and their elimination in fetal and neonatal periods.     

Differential isoelectric focusing properties of crude and purified human alpha 2-macroglobulin and alpha 2-macroglobulin-proteinase complexes

The isoelectric focusing (IEF) properties of human alpha 2-macroglobulin (alpha 2M) and alpha 2M-proteinase complexes from crude and partially purified preparations were studied by column IEF. The average isoelectric point (pI) of the major form was 6.5 for alpha 2M from crude plasma but was 5.3 for purified samples. Following preincubation with either trypsin, chymotrypsin or pancreatic elastase the crude alpha 2M-proteinase complexes displayed pI values ranging from 5.3 to 6.1 and the purified alpha 2M-proteinase complexes ranged from pH 6.0 to 6.1. A comparison of recoveries for focused crude or purified alpha 2M and trypsin-preincubated alpha 2M indicated enhanced recovery for the trypsin-preincubated samples suggesting that the binding of the proteinase enhances the stability of alpha 2M. alpha 2M thus displays column IEF properties which appear to be dependent upon the state of purity of the molecule. These findings are of particular significance to investigators concerned with using expressions of altered alpha 2M electrophoretic patterns for clinical diagnostic purposes in such diseases as multiple sclerosis, diabetes and cystic fibrosis.     

Separation of basic drug enantiomers by capillary electrophoresis using chicken alpha1-acid glycoprotein: insight into chiral recognition mechanism

Recombinant chicken alpha(1)-acid glycoprotein (alpha(1)-AGP) was prepared by the Escherichia coli expression system and completely deglycosylated alpha(1)-AGP (cd-alpha(1)-AGP) was obtained by treatments of native alpha(1)-AGP with a mixture of endoglycosidase and N-glycosidase. The average molecular masses of chicken alpha(1)-AGP, cd-alpha(1)-AGP and recombinant alpha(1)-AGP were estimated to be about 29 200, 21 700 and 20 700, respectively, by matrix-assisted laser desorption-time of flight-mass spectrometry. We compared the chiral recognition ability of chicken alpha(1)-AGP, cd-alpha(1)-AGP and recombinant alpha(1)-AGP using them as chiral selectors in capillary electrophoresis. The chicken alpha(1)-AGP showed higher resolution for eperisone, pindolol and tolperisone than cd-alpha(1)-AGP or recombinant alpha(1)-AGP. Recombinant alpha(1)-AGP still showed chiral recognition for three basic drugs tested. By addition of propranolol as a competitor in the separation solution in CE, no enantioseparations of three basic drugs were observed with chicken alpha(1)-AGP, cd-alpha(1)-AGP or recombinant alpha(1)-AGP. These results reveal that the protein domain of the chicken alpha(1)-AGP is responsible for the chiral recognition ability, and that the chiral recognition site(s) for basic drugs exists on the protein domain.     

Asymmetric synthesis of beta-amino acid derivatives incorporating a broad range of substitution patterns by enolate additions to tert-butanesulfinyl imines

Addition of Ti(Oi-Pr)(3) ester enolates to tert-butanesulfinyl aldimines and ketimines provided beta-substituted, alpha,beta- and beta,beta-disubstituted, alpha,beta,beta- and alpha,alpha,beta-trisubstituted, and alpha,alpha,beta,beta-tetrasubstituted beta-amino acid derivatives in high yields and with high diastereoselectivites. The N-sulfinyl-beta-amino ester products were further employed as versatile intermediates for both standard solution-phase and solid-phase synthetic transformations, including the synthesis of beta-peptide foldamers.     

广东乳源县瑶族人群α和β地中海贫血的分子流行病学调查

目的调查广东省乳源县瑶族人群中的α和β地中海贫血(简称地贫)的携带率、基因突变类型及其分布特征。方法连续收集905例父母双方或一方为广东省乳源县瑶族人群的新生儿脐带血及1 347例广东省乳源县瑶族人群婚检育龄成人的外周血分别进行α和β地贫调查;所有样品均进行RBC参数和血红蛋白电泳分析,对比各项检验指标。结果在905例脐带血样本中,检出Hb Bart's阳性样品52例;经基因分析,91例被确定了α地贫基因型(含92个突变等位基因,其中--SEA/43例、-α3.7/33例、-α4.2/9例、αWSα/2例、αCSα/3例、αQSα/1例)。值得注意的是,有38例-α3.7/αα和-α4.2/αα基因携带者检出自Hb Bart's阴性样品。结论研究为进行遗传咨询和制定该地区基于人群筛查的α和β地贫预防计划提供了有价值的基础资料。     

Metallation effects on the thermal interconversion of atropisomers of di(orthomethylarene)-substituted porphyrins

A new series of meso-substituted diaryl free-base and metalloporphyrins have been prepared. Each arene has been substituted with both a methyl group in the ortho position and a formyl group in the meta position. Rotation of the arene units is prevented at room temperature due to the steric restrictions imposed by the flanking methyl groups at the porphyrin beta-pyrrolic positions on the methyl groups at the ortho position on the meso-substituted arene unit. This allowed the alpha alpha and alpha beta atropisomers of this porphyrin to be separated and characterised. X-Ray crystallographic determination of the structure of the free-base porphyrin revealed a very flat porphyrin core. Metallation resulted in the isolation and characterisation of the nickel, zinc and copper derivatives. The assignments of the alpha alpha and alpha beta isomers are confirmed by X-ray crystallographic determination of the structures of the Cu(II) analogues. The copper alpha alpha structure exhibits a very twisted porphyrin core, the copper alpha beta structure is also distorted, but to a lesser degree. The activation energy for rotation has been calculated for each of the 2H, Ni and Zn derivatives. The energy required to rotate the arene ring increases in the order Ni < Zn approximately 2H. No significant difference in the free energy of rotation was observed between experiments carried out with the alpha alpha and small alpha beta isomers.     

New triterpene glucosides from the roots of Rosa laevigata Michx

Two new ursane-type triterpene glucosides, 2alpha,3alpha,24-trihydroxyurs-12,18-dien-28-oic acid beta-D-glucopyranosyl ester (1) and 2alpha,3alpha,23-trihydroxyurs-12,19(29)-dien-28-oic acid beta-D-glucopyranosyl ester (2), were isolated from the roots of Rosa laevigata, together with three known compounds: 2alpha,3beta,19alpha-trihydroxyurs-12-en-28-oic acid beta-Dglucopyranosyl ester (3), 2alpha,3alpha,19alpha-trihydroxyurs-12-en-28-oic acid beta-D-glucopyranosyl ester (4) and 2alpha,3beta,19alpha,23-tetrahydroxyurs-12-en-28-oic acid beta-D-glucopyranosyl ester (5). The structures of new compounds were established on the basis of detailed 1D and 2D NMR spectroscopic analyses. Compounds 2 and 5 exhibited modest in vitro antifungal activities against Candida albicans and C. krusei.