Synthesis Of Side Chain Research Articles

Highly (≥98%) Stereo‐ and Regioselective Trisubstituted Alkene Synthesis of Wide Applicability via 1‐Halo‐1‐alkyne Hydro‐ boration–Tandem Negishi–Suzuki Coupling or Organoborate Migratory Insertion

(Z)-1-Halo-1-alkenylboranes (7), preparable in 82-90% yields as ≥98% isomerically pure compounds via hydroboration of 1-halo-1-alkynes, have been converted to a wide range of trisubstituted alkenes via three different routes in the tail-to-head (T-to-H) direction, i.e., (i) Palladium-catalyzed Negishi-Suzuki tandem alkenylation, (ii) treatment of 7 with organolithium or Grignard reagents to generate α-bromo-1-alkenylboronate complexes (10) that can undergo migratory insertion of a carbon group (R2) to form (E)-alkenylboranes (11) with inversion of alkene configuration (≥98% inversion), followed by fluoride-promoted Suzuki alkenylation, and (iii) Negishi coupling to generate (Z)-alkenylboranes (8) in ≥98% retention of configuration, followed by treatment with organolithium or Grignard reagents to produce trisubstituted alkenes with reversed stereo configurations. The synthetic utility of the present methodology has been demonstrated in the highly selective synthesis of side chain (4) of scyphostatin in 28% yield over nine steps in the longest linear sequence from allyl alcohol. Thus, this new tandem protocol has been emerged as the most widely applicable and highly selective route to trisubstituted alkenes including those that are otherwise difficult to prepare.

Faulty Initiation of Proteoglycan Synthesis Causes Cardiac and Joint Defects

Proteoglycans are a major component of extracellular matrix and contribute to normal embryonic and postnatal development by ensuring tissue stability and signaling functions. We studied five patients with recessive joint dislocations and congenital heart defects, including bicuspid aortic valve (BAV) and aortic root dilatation. We identified linkage to chromosome 11 and detected a mutation (c.830G>A, p.Arg277Gln) in B3GAT3, the gene coding for glucuronosyltransferase-I (GlcAT-I). The enzyme catalyzes an initial step in the synthesis of glycosaminoglycan side chains of proteoglycans. Patients' cells as well as recombinant mutant protein showed reduced glucuronyltransferase activity. Patient fibroblasts demonstrated decreased levels of dermatan sulfate, chondroitin sulfate, and heparan sulfate proteoglycans, indicating that the defect in linker synthesis affected all three lines of O-glycanated proteoglycans. Further studies demonstrated that GlcAT-I resides in the cis and cis-medial Golgi apparatus and is expressed in the affected tissues, i.e., heart, aorta, and bone. The study shows that reduced GlcAT-I activity impairs skeletal as well as heart development and results in variable combinations of heart malformations, including mitral valve prolapse, ventricular septal defect, and bicuspid aortic valve. The described family constitutes a syndrome characterized by heart defects and joint dislocations resulting from altered initiation of proteoglycan synthesis (Larsen-like syndrome, B3GAT3 type).

Synthesis and characterization of polysulfone-containing sulfonated side chains for direct methanol fuel cells

Two series of novel polysulfone-based ionomers containing pendant sulfonic acid groups (designated as PSf-sph- y and PSf-sna- z) have been prepared using commercially available polysulfone and sulfoaryl monomers. The synthesized ionomers have been characterized by nuclear magnetic resonance, differential scanning calorimetry, and thermogravimetric analysis. The thermal characterization data show that these polymers are stable up to 210 °C in acid form and 270 °C in salt form in air. Ion exchange capacity, water uptake, swelling, proton conductivity, and methanol permeability of the membranes have been investigated and compared with those of Nafion 115. The PSf-sna- z membranes bearing highly ionic groups on the flexible side chains show lower water uptake, swelling, and methanol permeability compared to the PSf-sph- y and Nafion 115 membranes. The optimized PSf-sna-58 membrane shows better performance in direct methanol fuel cells (DMFC) than Nafion 115 membranes.

SPOT Peptide Arrays to Study Biological Interfaces at the Molecular Level

A detailed knowledge on how proteins interact with other proteins or nucleic acids is essential for basic research as well as for the development of drugs and therapeutic leads. In this context, peptide arrays represent a powerful tool to analyze individual interactions within complex protein networks. Moreover, peptide arrays allow for incorporation of artificial building blocks during synthesis and secondary modification of amino acid side chains after synthesis, which makes them even more versatile. Within this review, we summarize the spectrum of applications of solid-supported peptide arrays generated by the SPOT method and provide an introduction into the entire volume dedicated to the topic. Keywords: Epitope mapping, peptide synthesis, protein-protein interaction, protein-RNA interaction, proteomics, SPOT, protein, Peptide arrays, complex protein

Synthesis and cytotoxic evaluation of 1-carboxamide and 1-amino side chain substituted β-carbolines

The condensation of alkylenediamine with ethyl β-carboline-1-carboxylate and 1-bromo-β-carboline gave β-carboline-1-carboxamides and 1-amino-β-carbolines, respectively. Some of these β-carbolines were active against a panel of human tumor cell lines, and 1-amino derivatives were more potent than their 1-carboxamide congeners. In particular, among the 1-amino-β-carbolines, the N 9-arylated alkyl substituted β-carbolines exhibited the most interesting cytotoxic activities with IC 50 value of lower than 20 μM. The preliminary structure–activity relationships (SARs) analysis suggested that (1) 1-amino substituents were the advisable pharmacophoric group for enhanced cytotoxic activities; (2) the introduction of appropriate arylated alkyl groups into position-9 of β-carboline facilitated their cytotoxic potencies.

ChemInform Abstract: Palladium Catalysis in Cephalosporin Chemistry: General Methodology for the Synthesis of Cephem Side Chains.

ChemInform Abstract: Palladium Catalysis in Cephalosporin Chemistry: General Methodology for the Synthesis of Cephem Side Chains.

Novel biosynthesis of (R)-ethyl-3-hydroxyglutarate with (R)-enantioselective hydrolysis of racemic ethyl 4-cyano-3-hydroxybutyate by Rhodococcus erythropolis

(R)-ethyl-3-hydroxyglutarate with highly optical purity (> or = 99%) can be used as a novel precursor for synthesis of chiral side chain of rosuvastatin. In this study, a novel synthesis route of (R)-ethyl-3-hydroxyglutarate by whole microorganism cells from racemic ethyl 4-cyano-3-hydroxybutyate was created. A strain ZJB-0910 capable of transforming racemic beta-hydroxy aliphatic nitrile was isolated by employing a screening method based on a colorimetric reaction of Co(2+) ion with ammonia, and identified as Rhodococcus erythropolis based on its morphology, physiological tests, Biolog, and the 16S rDNA sequence. After cultivation in a sterilized medium with composition of 20 g glucose, 5 g yeast extract, 0.5 g KH(2)PO(4), 0.5 g K(2)HPO(4), 0.2 g MgSO(4).7H(2)O per liter at 30 degrees C and 150 rpm for 48 h, the whole cells of R. erythropolis ZJB-0910 were prepared as a catalyst in (R)-enantioselective hydrolysis of racemic ethyl 4-cyano-3-hydroxybutyate for synthesis of (R)-ethyl-3-hydroxyglutarate, without bearing hydrolase activity for the ester bond of ethyl 4-cyano-3-hydroxybutyate. Under the optimized biotransformation conditions of pH 7.5, 30 degrees C,and 20 mM substrate concentration, (R)-ethyl-3-hydroxyglutarate with 46.2% yield (ee>99%) was afforded, and its chemical structure was determined by ESI-MS, NMR, and IR. The apparent Michaelis constant K(m) and maximum rate Vmax for this biocatalytic reaction were 0.01 M and 85.6 micromol min(-1)g(-1), respectively.

An Efficient Synthesis of Taxotere Side Chain

An efficient synthesis of taxotere side chain has been achieved using Shibasakis asymmetric Henry reaction as the key step. Keywords: Taxol, Taxotere side chain, Anticancer agents, Asymmetric synthesis, Asymmetric Henry reaction, La-(R)-BINOL

Stereoselective introduction of two chiral centers by a single diketoreductase: an efficient biocatalytic route for the synthesis of statin side chains

Statins, including atorvastatin (Lipitor), are the top-selling drugs in the world. The biocatalytic production of chiral side chains of statin drugs is of great interest to academia and industry. Stereoselective double reduction of a beta,delta-diketo ester catalyzed by a diketoreductase offers a simple and efficient route for the preparation of statin side chains. Comparison of different cofactor regeneration systems resulted in an easy and cost-effective process for this enzymatic reduction.

Cis-(-)-Menthyl phenylglycidates in the asymmetric synthesis of taxol side chain

The one-pot azidation and benzoylation of a mixture of cis (-)-menthyl phenylglycidates provide quantitatively the corresponding (2R,3S)-, and (2S,3R)-3-azido-1-((1R,2S,5R)-2-isopropyl-5methylcyclohexyloxy)-1-oxo-3-phenylpropan-2-yl benzoate. Enantiopure (2R,3S)-3-azido-1((1R,2S,5R)-2-isopropyl-5-methylcyclohexyloxy)-1-oxo-3-phenylpropan-2-yl benzoate crystallize from MeOH at room temperature in high yields. The reduction of the latter with Zn-TMSCl produces (-)-menthyl 3-benzamido-3-phenyl-2-(trimethylsilyloxy)propanoate which upon simultanious desilylation and hydrolysis provide the taxol side chain N-benzoyl-(2R,3S)-3phenylisoserine.

Stereoselective Construction of Steroidal Side Chain from 16-Dehydropregnenolone Acetate

Stereoselective construction of steroidal side chain at C-20 having ‘natural’ configuration using 16-dehydropregnalone acetate (16-DPA) as a starting material has been carried out. Palladium-catalyzed carbon-carbon bond-forming Heck reaction between C-20 vinyl iodide with methyl acrylate and transfer hydrogenation with triethylsilane and Pd/C are the key steps for stereoselective side-chain synthesis.

Synthesis and Antimalarial Activity of Novel Side Chain Modified Antimalarial Agents Derived from 4-Aminoquinoline

Malaria is one of the foremost public health problems in developing countries affecting nearly 40% of the global population. Apart from this, the past two decade's emergence of drug resistance has severely limited the choice of available antimalarial drugs. Furthermore, the general trend emerging from the SAR-studies is that chloroquine resistance does not involve any change to the target of this class of drugs but involves compound specific efflux mechanism. Based on this premise a number of groups have developed short chain analogues of 4-aminoquinoline, which are active against CQ-resistant strains of P. falciparum in in vitro studies. However, these derivatives undergo biotransformation (de-alklyation) significantly affecting lipid solubility of the drug. In view of this background information, we thought that it would be interesting to study the effect of additional lipophilicity and cationic charge at the lateral side chain of 4-aminoquinoline. This prompted us to explore the cationic amino acid conjugates namely, lysine and ornithine of 4-aminoquinoline with a view to achieve improved antimalarial activity and to the best of our knowledge such amino acid conjugates have not been hitherto reported in the literature in the case of 4-aminoquinolines. In the present study, a new series of side-chain modified 4-aminoquinolines have been synthesized and found active against both susceptible and multidrug resistant strains of P. falciparum in vitro and P. yoelli in vivo. The seminal finding of the present study is that a new series of compounds having significantly more activity against CQ resistant parasites has been identified.

A genome-wide screen identifies genes required for formation of the wobble nucleoside 5-methoxycarbonylmethyl-2-thiouridine in Saccharomyces cerevisiae

We recently showed that the gamma-subunit of Kluyveromyces lactis killer toxin (gamma-toxin) is a tRNA endonuclease that cleaves tRNA(mcm5s2UUC Glu), tRNA(mcm5s2UUU Lys), and tRNA(mcm5s2UUG Gln) 3' of the wobble nucleoside 5-methoxycarbonylmethyl-2-thiouridine (mcm(5)s(2)U). The 5-methoxycarbonylmethyl (mcm(5)) side chain was important for efficient cleavage by gamma-toxin, and defects in mcm(5) side-chain synthesis correlated with resistance to gamma-toxin. Based on this correlation, a genome-wide screen was performed to identify gene products involved in the formation of the mcm(5) side chain. From a collection of 4826 homozygous diploid Saccharomyces cerevisiae strains, each with one nonessential gene deleted, 63 mutants resistant to Kluyveromyces lactis killer toxin were identified. Among these, eight were earlier identified to have a defect in formation of the mcm(5) side chain. Analysis of the remaining mutants and other known gamma-toxin resistant mutants revealed that sit4, kti14, and KTI5 mutants also have a defect in the formation of mcm(5). A mutant lacking two of the Sit4-associated proteins, Sap185 and Sap190, displays the same modification defect as a sit4-null mutant. Interestingly, several mutants were found to be defective in the synthesis of the 2-thio (s(2)) group of the mcm(5)s(2)U nucleoside. In addition to earlier described mutants, formation of the s(2) group was also abolished in urm1, uba4, and ncs2 mutants and decreased in the yor251c mutant. Like the absence of the mcm(5) side chain, the lack of the s(2) group renders tRNA(mcm5s2UUC Glu) less sensitive to gamma-toxin, reinforcing the importance of the wobble nucleoside mcm(5)s(2)U for tRNA cleavage by gamma-toxin.

Monoquaternary pyridinium salts with modified side chain—synthesis and evaluation on model of tabun- and paraoxon-inhibited acetylcholinesterase

Acetylcholinesterase reactivators are crucial antidotes for the treatment of organophosphate intoxication. Eighteen monoquaternary reactivators of acetylcholinesterase with modified side chain were developed in an effort to extend the properties of pralidoxime. The known reactivators (pralidoxime, HI-6, obidoxime, trimedoxime, methoxime) and the prepared compounds were tested in vitro on a model of tabun- and paraoxon-inhibited AChE. Monoquaternary reactivators were not able to exceed the best known compounds for tabun poisoning, but some of them did show reactivation better or comparable with pralidoxime for paraoxon poisoning. However, extensive differences were found by a SAR study for various side chains on the non-oxime part of the reactivator molecule.

Multigenome analysis identifies a worldwide distributed epidemic Legionella pneumophila clone that emerged within a highly diverse species

Genomics can provide the basis for understanding the evolution of emerging, lethal human pathogens such as Legionella pneumophila, the causative agent of Legionnaires' disease. This bacterium replicates within amoebae and persists in the environment as a free-living microbe. Among the many Legionella species described, L. pneumophila is associated with 90% of human disease and within the 15 serogroups (Sg), L. pneumophila Sg1 causes over 84% of Legionnaires' disease worldwide. Why L. pneumophila Sg1 is so predominant is unknown. Here, we report the first comprehensive screen of the gene content of 217 L. pneumophila and 32 non-L. pneumophila strains isolated from humans and the environment using a Legionella DNA-array. Strikingly, we uncovered a high conservation of virulence- and eukaryotic-like genes, indicating strong environmental selection pressures for their preservation. No specific hybridization profile differentiated clinical and environmental strains or strains of different serogroups. Surprisingly, the gene cluster coding the determinants of the core and the O side-chain synthesis of the lipopolysaccaride (LPS cluster) determining Sg1 was present in diverse genomic backgrounds, strongly implicating the LPS of Sg1 itself as a principal cause of the high prevalence of Sg1 strains in human disease and suggesting that the LPS cluster can be transferred horizontally. Genomic analysis also revealed that L. pneumophila is a genetically diverse species, in part due to horizontal gene transfer of mobile genetic elements among L. pneumophila strains, but also between different Legionella species. However, the genomic background also plays a role in disease causation as demonstrated by the identification of a globally distributed epidemic strain exhibiting the genotype of the sequenced L. pneumophila strain Paris.

A Short Method for the Synthesis of Alpha-Tocopherol Side Chain

The enzymatic hydrolysis of meso-1,7-diac etoxy-2,6-dimethylheptane 5, prepared from 2,6-dimethylhepta-1,6-diene 6, gave the (2S,6R)-7-acetoxy-2,6-dimethyl-1-heptanol 1, which was transformed to the (2R,6R)-2,6,10-trimethyl-1-undecanol 7. In this manner, the C14 side chain of α-Tocopherol was synthesized from 2,6-dimethylhepta-1,6-diene 6 in only 5 steps.

Determination of enantiomeric excess of ethyl 3,5‐dihydroxy‐6‐benzyloxy hexanoate by chiral reverse phase high performance liquid chromatography

A simple and reliable chiral HPLC method was developed for the determination of enantiomeric excess of a chiral dihydroxy intermediate for the chemoenzymatic synthesis of side chain of statin drugs. After evaluating different columns and conditions, the four stereoisomers of ethyl 3,5-dihydroxy-6-benzyloxy hexanoate were well resolved by a simple gradient elution on OD-RH column, and the enantiomeric excess of the desired 3R,5S-enantiomer was accurately measured. This study provides a simple, rapid, accurate, and reliable method to assess the enantiomeric quality of such important intermediates.

Specificity of L,D-Transpeptidases from Gram-positive Bacteria Producing Different Peptidoglycan Chemotypes

We report here the first direct assessment of the specificity of a class of peptidoglycan cross-linking enzymes, the L,D-transpeptidases, for the highly diverse structure of peptidoglycan precursors of Gram-positive bacteria. The lone functionally characterized member of this new family of active site cysteine peptidases, Ldt(fm) from Enterococcus faecium, was previously shown to bypass the D,D-transpeptidase activity of the classical penicillin-binding proteins leading to high level cross-resistance to glycopeptide and beta-lactam antibiotics. Ldt(fm) homologues from Bacillus subtilis (Ldt(Bs)) and E. faecalis (Ldt(fs)) were found here to cross-link their cognate disaccharide-peptide subunits containing meso-diaminopimelic acid (mesoDAP(3)) and L-Lys(3)-L-Ala-L-Ala at the third position of the stem peptide, respectively, instead of L-Lys(3)-d-iAsn in E. faecium. Ldt(fs) differed from Ldt(fm) and Ldt(Bs) by its capacity to hydrolyze the L-Lys(3)-D-Ala(4) bond of tetrapeptide (L,D-carboxypeptidase activity) and pentapeptide (L,D-endopeptidase activity) stems, in addition to the common cross-linking activity. The three enzymes were specific for their cognate acyl acceptors in the cross-linking reaction. In contrast to Ldt(fs), which was also specific for its cognate acyl donor, Ldt(fm) tolerated substitution of L-Lys(3)-D-iAsn by L-Lys(3)-L-Ala-L-Ala. Likewise, Ldt(Bs) tolerated substitution of mesoDAP(3) by L-Lys(3)-D-iAsn and L-Lys(3)-L-Ala-L-Ala in the acyl donor. Thus, diversification of the structure of peptidoglycan precursors associated with speciation has led to a parallel evolution of the substrate specificity of the L,D-transpeptidases affecting mainly the recognition of the acyl acceptor. Blocking the assembly of the side chain could therefore be used to combat antibiotic resistance involving L,D-transpeptidases.

Mutations Blocking Side Chain Assembly, Polymerization, or Transport of a Wzy-DependentStreptococcus pneumoniaeCapsule Are Lethal in the Absence of Suppressor Mutations and Can Affect Polymer Transfer to the Cell Wall

Extracellular polysaccharides of many bacteria are synthesized by the Wzy polymerase-dependent mechanism, where long-chain polymers are assembled from undecaprenyl-phosphate-linked repeat units on the outer face of the cytoplasmic membrane. In gram-positive bacteria, Wzy-dependent capsules remain largely cell associated via membrane and peptidoglycan linkages. Like many Wzy-dependent capsules, the Streptococcus pneumoniae serotype 2 capsule is branched. In this study, we found that deletions of cps2K, cps2J, or cps2H, which encode a UDP-glucose dehydrogenase necessary for side chain synthesis, the putative Wzx transporter (flippase), and the putative Wzy polymerase, respectively, were obtained only in the presence of suppressor mutations. Most of the suppressor mutations were in cps2E, which encodes the initiating glycosyltransferase for capsule synthesis. The cps2K mutants containing the suppressor mutations produced low levels of high-molecular-weight polymer that was detected only in membrane fractions. cps2K-repaired mutants exhibited only modest increases in capsule production due to the effect of the secondary mutation, but capsule was detectable in both membrane and cell wall fractions. Lethality of the cps2K, cps2J, and cps2H mutations was likely due to sequestration of undecaprenyl-phosphate in the capsule pathway and either preclusion of its turnover for utilization in essential pathways or destabilization of the membrane due to an accumulation of lipid-linked intermediates. The results demonstrate that proper polymer assembly requires not only a functional transporter and polymerase but also complete repeat units. A central role for the initiating glycosyltransferase in controlling capsule synthesis is also suggested.

Cloning and expression of the gene encoding solanesyl diphosphate synthase from Hevea brasiliensis

Summary Plastoquinones play important roles as electron carriers in the light-dependent reactions of photosynthesis and also as a cofactor of phytoene desaturation in the synthesis of carotenoid. A plastoquinone-9 (PQ-9) was identified in Frey-Wyssling organelles of fresh rubber latex from Hevea brasiliensis. This indicates that a Hevea solanesyl diphosphate synthase (HbSDS) must be present for the synthesis of the C45 prenyl side chain of the PQ-9 found in the rubber latex. Based on the sequence information of other trans-prenyl diphosphate synthases, the cDNA encoding HbSDS was cloned from aHevearubberlatexcDNAlibrary.Sequence analysis revealed the presence of an ORFconsisting of 1254 bpcapable of encoding a 46,095 Da polypeptide. The deduced amino acid sequence of the clone contained all conserved regions found in typical trans-prenyl chain elongating enzymes. This cDNA, expressed in Escherichia coli cells as an insoluble but Trx-His-tagged fusion protein, showed a distinct solanesyl diphosphate synthase activity in the presence of Triton X-100. The expression level of HbSDS mRNA in latex was found to be higher than those in leaves, stems and roots. The expressed HbSDS is suggested to be a specific enzyme in the Frey-Wyssling particles of rubber latex. # 2007 Elsevier Ireland Ltd. All rights reserved.