Revisiting the aldol reaction of cis-α,β-epoxyaldehyde promoted by BF(3)·Et(2)O: direct access to 2-deoxy-2-fluoro heptulosonic ester analogues

The aldol reaction between cis-3-((tert-butyldiphenylsilyloxy)methyl)oxirane-2-carbaldehyde and ethyl-2-(trimethylsilyloxy)-2-propenoate promoted by boron trifluoride diethyl etherate was reinvestigated. By varying the work-up conditions, a new 2-deoxy-2-fluoro heptulosonic ester analogue was synthesized. Derivatizations and detailed NMR analysis allowed the complete characterization of this fluoro analogue and its derivatives.     

Synthesis of 2-acetamido-1-N[N-(tert-butoxycarbonyl)-l-aspart-1-oyl-(l-phenylalanyl-l-serine methyl ester)-4-oyl]-2-deoxy-β-d-glucopyranosylamine and analogs

2-Acetamido-1-N-[N-(tert-butoxycarbonyl)-l-aspart-1-oyl-(l-phenylalanyl-l-serine methyl ester)-4-oyl]-2-deoxy-β-d-glucopyranosylamine and analogs containing d-glucopyranosyl, 4-O-β-d-glucopyranosyl-d-glucopyranosyl, l-Phe-l-Ala, and d-Phe-l-Ser were synthesized by condensation of glycosylamines having free hydroxyl groups with tripeptide esters activated with N-hydroxysuccinimide.     

Characterization of 5-Chloro-5-Deoxy-d-Ribose 1-Dehydrogenase in Chloroethylmalonyl Coenzyme A Biosynthesis: SUBSTRATE AND REACTION PROFILING*

SalM is a short-chain dehydrogenase/reductase enzyme from the marine actinomycete Salinispora tropica that is involved in the biosynthesis of chloroethylmalonyl-CoA, a novel halogenated polyketide synthase extender unit of the proteasome inhibitor salinosporamide A. SalM was heterologously overexpressed in Escherichia coli and characterized in vitro for its substrate specificity, kinetics, and reaction profile. A sensitive real-time ¹³C NMR assay was developed to visualize the oxidation of 5-chloro-5-deoxy-d-ribose to 5-chloro-5-deoxy-d-ribono-γ-lactone in an NAD⁺-dependent reaction, followed by spontaneous lactone hydrolysis to 5-chloro-5-deoxy-d-ribonate. Although short-chain dehydrogenase/reductase enzymes are widely regarded as metal-independent, a strong divalent metal cation dependence for Mg²⁺, Ca²⁺, or Mn²⁺ was observed with SalM. Oxidative activity was also measured with the alternative substrates d-erythrose and d-ribose, making SalM the first reported stereospecific non-phosphorylative ribose 1-dehydrogenase.     

The metabolism of 3,5-di-tert.-butyl-4-hydroxytoluene in the rat and in man

1. The major metabolites of 3,5-di-tert.-butyl-4-hydroxytoluene (BHT) in the rat are 3,5-di-tert.-butyl-4-hydroxybenzoic acid (BHT-acid), both free (9% of the dose) and as a glucuronide (15%), and S-(3,5-di-tert.-butyl-4-hydroxybenzyl)-N-acetylcysteine. 2. The mercapturic acid does not appear to derive from the usually accepted enzyme mechanism, and may involve a non-enzymic reaction between BHT free radical and cysteine. 3. The ester glucuronide and mercapturic acid found in rat urine are also the major metabolites in rat bile and must be responsible for the enterohepatic circulation. 4. Free BHT-acid is the main component in rat faeces. 5. In man, BHT-acid, free and conjugated, is a minor component in urine, and the mercapturic acid is virtually absent. The bulk of the radioactivity is excreted as the ether-insoluble glucuronide of a metabolite in which the ring methyl group and one tert.-butyl methyl group are oxidized to carboxyl groups, and a methyl group on the other tert.-butyl group is also oxidized, probably to an aldehyde group. 6. These differences in metabolism by the rat and by man are sufficient to account for the difference in excretion by the two species.     

Enantioselective ester hydrolase from Sphingobacterium sp. 238C5 useful for chiral resolution of β-phenylalanine and for its β-peptide synthesis

A novel enzyme, β-phenylalanine ester hydrolase, useful for chiral resolution of β-phenylalanine and for its β-peptide synthesis was characterized. The enzyme purified from the cell free-extract of Sphingobacterium sp. 238C5 well hydrolyzed β-phenylalanine esters (S)-stereospecifically. Besides β-phenylalanine esters, the enzyme catalyzed the hydrolysis of several α-amino acid esters with l-stereospecificity, while the deduced 369 amino acid sequence of the enzyme exhibited homology to alkaline d-stereospecific peptide hydrolases from Bacillus strains. Escherichia coli transformant expressing the β-phenylalanine ester hydrolase gene exhibited an about 8-fold increase in specific (S)-β-phenylalanine ethyl ester hydrolysis as compared with that of Sphingobacterium sp. 238C5. The E. coli transformant showed (S)-enantiomer specific esterase activity in the reaction with a low concentration (30 mM) of β-phenylalanine ethyl ester, while it showed both esterase and transpeptidase activity in the reaction with a high concentration (170 mM) of β-phenylalanine ethyl ester and produced β-phenylalanyl-β-phenylalanine ethyl ester. This transpeptidase activity was useful for β-phenylalanine β-peptide synthesis.     

Total synthesis of 12,13-desoxyepothilone B (Epothilone D)

A highly convergent total synthesis of 12,13-desoxyepothilone B (4, Epothilone D) is described involving the coupling of vinyl iodide (5) and olefin (6). Key steps in the synthesis are the introduction of chirality at C15 via highly enantioselective lipase-mediated enzymatic resolution, diastereoselective alkylation at C8, highly diastereoselective Evans aldol reaction to establish C6-C7, and Mukaiyama aldol reaction to introduce chiral center C3. Palladium catalyzed Suzuki coupling of (5) and (6) provided the methyl ester (27), which was converted to 12,13-desoxyepothilone B (4).     

Synthesis of Novel 4′α-Trifluoromethyl-2′β-C-Methyl-Carbodine Analogs as Anti-Hepatitis C Virus Agents

Novel 4?′α-trifluoromethyl-2?′β-methyl carbocyclic nucleoside analogs have been prepared and evaluated for inhibition of hepatitis C virus (HCV) RNA replication in cell cultures. Construction of cyclopentene intermediate 10a was achieved via sequential Johnson–Claisen orthoester rearrangement and ring-closing metathesis starting from the α-trifluoromethyl-α,β-unsaturated ester 5. Stereoselective dihydroxylation and desilylation yielded the target carbodine analogs. The synthesized nucleoside analogs mentioned above (18 and 19) were assayed for their ability to inhibit HCV RNA replication in a subgenomic replicon Huh7 cell line (LucNeo#2). However, the synthesized nucleosides showed neither significant antiviral activity nor toxicity up to 50 μM.     

Synthesis of 5-thio-D-galactose

A synthesis of 5-thio-D-galactose, in the form of its crystalline, anomeric methyl glycopyranosides, is described. Compounds prepared as intermediates included ethyl 2,3-di-O-(tert-butyldimethylsilyl)-5,6-O-carbonyl-β-D-galactofuranoside, the corresponding 5,6-dideoxy-5,6-epithio derivative, and ethyl 2,3,6-tri-O-acetyl-5-S-acetyl-5-thio-β-D-galactofuranoside. On methanolysis, the latter afforded methyl 5-thio-α-D-galactopyranoside which, in turn, was transformed into methyl 5-thio-β-D-galactopyranoside. Acetolysis proved to be less satisfactory for incorporation of the sulfur atom into a pyranose ring-form. Characteristics of the ¹³C-n.m.r. spectra of derivatives of 5-thio-D-galactose are described, including the fact that ¹J_C,H values for the anomeric pyranosides differ by only 1–3 Hz, as compared with ≈ 10 Hz for their oxygen analogs.     

Synthesis of [19, 35, 36-13C3]-labeled TAK779 as a molecular probe

N,N-Dimethyl-N-[4-[[[2-(4-methylphenyl)-6,7-dihydro-5H-benzocyclohepten-8-yl]carbonyl]amino]benzyl]tetrahydro-2H-pyran-4-aminium chloride (TAK779) is a potent and selective non-peptide CCR5 antagonist. To use a site-specifically labeled form as a molecular probe, TAK779 containing ¹³C at positions C19, 35, and 36 was produced. A commercially available [¹³C]-methyl iodide was employed for the labeling. Starting from a known carboxylic acid segment containing no labeled carbon, the labeled TAK779 was constructed by the successive coupling of [¹³C]-labeled tolyl boronic ester by the Suzuki–Miyaura reaction and a [¹³C]-labeled aniline segment by amide bond formation.     

Lipase resolution of new (±)-3-aryloxy-1-halogenopropan-2-ols: Versatile building blocks for β-adrenergic receptor antagonists

Using two commercial immobilized lipases Lipozyme^® TL and Novozym^® 435 effective kinetic resolution of several novel 3-aryloxy-1-halogenopropan-2-ols was achieved by acyl transfer reaction in organic solvents, yielding both enantiomers with 89–99% ee. In preparative resolutions carried out in tert-butyl methyl ether at 25 °C with vinyl acetate as acyl donor enantioselectivity ratio E was from 64 to 99. The resolved enantiomers were successfully used as chiral building blocks in the synthesis of new 1-alkylamino-3-aryloxypropan-2-ols, by nucleophilic halogen substitution with isopropylamine and tert-butylamine. The obtained products will be evaluated in vitro as potential new β-adrenergic receptors antagonists.     

Efficient synthesis of ruthenium complexes of the type (R-bpy)2RuCl2 and [(R-bpy)2Ru(L-L)]Cl2 by microwave-activated reactions (R: H, Me, tert-But) (L-L: substituted bibenzimidazoles, bipyrimidine, and phenanthroline)

Complexes of the type (R-bpy)₂RuCl₂ (R: H, Me, tert-but) were synthesised by microwave-activated reactions of [Ru(cod)Cl₂]_n with substituted 2,2′-bipyridines in dimethylformamide as the solvent. The complexes were isolated in high yields and high purity from the reaction mixture. Microwave-assisted or thermal reaction of the (R-bpy)₂RuCl₂ solutions with substituted bibenzimidazoles, 1,10 phenanthroline or bipyrimidine in dmf/water mixtures resulted in the formation of mixed ligand complexes of the type [(R-bpy)₂Ru(L-L)]Cl₂. The complexes were characterised by NMR spectroscopy and MS. Furthermore, their photochemical and electrochemical properties were investigated and the solid state structure of (4-tert-butyl-bpy)₂RuCl₂ (3), [(4-tert-butyl-bpy)₂Ru(tetramethylbibenzimidazole)](PF₆)₂ (4), and [(4-tert-butyl-bpy)₂Ru(bipyrimidine] (PF₆)₂ (5) was determined by X-ray diffraction analysis of single crystals.     

Synthesis of 2,6-di(acylamino)-2,6-dideoxy-3-O-(d-2-propanoyl-l-alanyl-d-isoglutamine)-d-glucopyranoses

Five 2,6-di(acylamino)-2,6-dideoxy-3-O-(d-2-propanoyl-l-alanyl-d-isoglutamine)-d-glucopyranoses (lipophilic, muramoyl dipeptide analogs) were synthesized from benzyl 2-(benzyloxycarbonylamino)-3-O-(d-1-carboxyethyl)-2-deoxy-5,6-O-isopropylidene-β-dglucopyranoside (1). Methanesulfonylation of 3, derived from the methyl ester of 1 by O-deisopropylidenation, gave the 6-methanesulfonate (4). (Tetrahydropyran-2-yl)ation of 4 gave benzyl 2-(benzyloxycarbonylamino)-2-deoxy-3-O-[d-1-(methoxycarbonyl)ethyl]-6-O-(methylsulfonyl)-5-O-(tetrahydropyran-2-yl)-β-d- glucofuranoside, which was treated with sodium azide to give the corresponding 6-azido derivative (6). Condensation of benzyl 6-amino-2-(benzyloxycarbonyl-amino)-2,6-dideoxy-3-O-[d-1-(methoxycarbonyl)ethyl]-5-O-(tetrahydropyran-2-yl)-β-d-glucofuranoside, derived from 6 by reduction, with the activated esters of octanoic, hexadecanoic, and eicosanoic acid gave the corresponding 6-N-fatty acyl derivatives (8–10). Coupling of the 2-amino derivatives, obtained from compounds 8, 9, and 10 by catalytic reduction, with the activated esters of the fatty acids, gave the 2,6-(diacylamino)-2,6-dideoxy derivatives (11–15). Condensation of the acids, formed from 11–15 by de-esterification, with the benzyl ester of l-alanyl-d-isoglutamine, and subsequent hydrolysis, afforded benzyl 2,6-di(acylamino)-2,6-dideoxy-3-O-(d-2-propanoyl-l-alanyl-d-isoglutamine benzyl ester)-β-d-glucofuranosides. Hydrogenation of the dipeptide derivatives thus obtained gave the five lipophilic analogs of 6-amino-6-deoxymuramoyl dipeptide, respectively, in good yields.     

Hydrolysis of novel diacylglycerol and phorbol diesters by serum lipase

Rat serum, active in the hydrolysis of the tumor-promoting phorbol diester, 12-O-tetradecanoylphorbol-13-acetate (TPA), was examined with regard to lipid interferences of [³H]TPA hydrolysis and enzyme substrate specificity. The enzymatic hydrolysis of TPA could be enhanced 8-fold, ever crude serum, by using a lipid-free acetone powder of rat serum. Addition of lipid to the lipid-free acetone powder produced potent inhibition of TPA hydrolysis. The inclusion of multilamallar liposomes resulted in similar inhibition, and isolation of liposomes by high-speed centrifugation showed that 95% of the radiolabeled TPA was associated with the fatty pellet. Substrate specificity studies demonstrated that the serum activity hydrolyzes the long-chain ester of TPA and the long-chain primary acyl group of diacylglycerols. TPA was hydrolyzed at approximately twice the rate of dioleoylglycerol; however, the most reactive substrates were those synthetic analogs of diacylglycerol containing a short-chain ester group at the sn-2 position. Palmitic acid was liberated from [1-¹⁴C]palmitoyl-2-acetyl-sn-glycerol and [1-¹⁴C]palmitoyl-2-butyryl-sn-glycerol at 120- and 33-tinies the rate of TPA hydrolysis, respectively. Lipase resistant 1-hexadecyl-2-[³H]acetylglycerol was also used as substrate, but the sn-2 ester moiety showed poor lability. The diacylglycerol analogs are new lipase substrates and, in view of their similarities to the fatty acyl portion of TPA, it is thought that these compounds could serve as protein kinase C activators.     

A sialic acid aldolase from Peptoclostridium difficile NAP08 with 4-hydroxy-2-oxo-pentanoate aldolase activity

Sialic acid aldolases (E.C.4.1.3.3) catalyze the reversible aldol cleavage of N-acetyl-d-neuraminic acid (Neu5Ac) to from N-acetyl-d-mannosamine (ManNAc) and pyruvate. In this study, a sialic acid aldolase (PdNAL) from Peptoclostridium difficile NAP08 was expressed in Escherichia coli BL21 (DE3). This homotetrameric enzyme was purified with a specific activity of 18.34 U/mg for the cleavage of Neu5Ac. The optimal pH and temperature for aldol addition reaction were 7.4 and 65 °C, respectively. PdNAL was quite stable at neutral and alkaline pH (6.0–10.0) and maintained about 89% of the activity after incubation at pH 10.0 for 24 h. After incubation at 70 °C for 15 min, almost no activity loss was observed. The high thermostability simplified the purification of this enzyme. Interestingly, substrate profiling showed that PdNAL not only accepted ManNAc but also short chain aliphatic aldehydes such as acetaldehyde, propionaldehyde and n-butyraldehyde as the substrates. This is the first example that a sialic acid aldolase is active toward aliphatic aldehyde acceptors with two or more carbons. The amino acid sequence analysis indicates that PdNAL belongs to the NAL subfamily rather than 4-hydroxy-2-oxopentanoate (HOPA) aldolase, but it is interesting that the enzyme possesses the activity of HOPA aldolase.     

Synthesis and Structure?Activity Relationships of Antifungal Crassinervic Acid Analogs

A series of analogs of the natural antifungal compound crassinervic acid, a constituent of Piper crassinervium, were synthesized to gain insight into the most relevant structural features affecting the activity of the parent molecule. Most compounds were prepared by aldol reaction of methyl 3‐acetyl‐4‐hydroxybenzoate with a series of ketones, followed by reduction, hydrolysis, and oxidation. The antifungal activities of crassinervic acid and its analogs was assessed against Cladosporium cladosporioides by using the method of bioautography. The bioassay results allowed us to depict structure? activity relationships for this class of compounds.     

A sterically congested aryltrimethylstannane - Synthesis, reactivity, transmetalation and CH-π interaction

The synthesis of a novel sterically congested tetraorganotin compound, (4-tert-butyl-2,6-dimesitylphenyl)trimethylstannane (1), is reported and its reactivity with special focus on transmetalation studied. The reaction of compound 1 with reagents such as HgCl₂, BiCl₃ and HOTf gave (4-tert-butyl-2,6-dimesitylphenyl)dimethyltin chloride (2) and (4-tert-butyl-2,6-dimesitylphenyl)dimethyltin triflate (3), respectively, as a result of selective tin-methyl bond cleavage. Less bulky aryltrimethyltin derivatives react with BiCl₃ to give both tin-methyl and tin-aryl bond cleavage. Hydrolysis of compound 3 proceeds slowly to give bis-(4-tert-butyl-2,6-dimesitylphenyl)dimethyl stannoxane (5) via the intermediate (4-tert-butyl-2,6-dimesitylphenyl)dimethyltin hydroxide (4). All terphenyldimethyltin derivatives that were characterized by single crystal X-ray diffraction analysis show C-H?π interactions. Based on these results, the optimum C-H?π distance (C?centroid_aryl distance) is suggested to be in the range 3.4 and 3.5 Å.     

Catalytic asymmetric synthesis of α-methyl-p-boronophenylalanine

p-Boronophenylalanine (l-BPA) is applied in clinical settings as a boron carrier for boron neutron capture therapy (BNCT) to cure malignant melanomas. Structural modification or derivatization of l-BPA, however, to improve its uptake efficiency into tumor cells has scarcely been investigated. We successfully synthesized (S)-2-amino-3-(4-boronophenyl)-2-methylpropanoic acid in enantioenriched form as a novel candidate molecule for BNCT. Key steps to enhance the efficiency of this synthesis were enantioselective alkylation of N-protected alanine tert-butyl ester with a Maruoka catalyst and Miyaura borylation reaction to install the boron functionality.     

Characterization of CYP1A2, CYP2C19, CYP3A4 and CYP3A5 polymorphisms in South Brazilians

Potential causes of variability in drug response include intrinsic factors such as ethnicity and genetic differences in the expression of enzymes that metabolize drugs, such as those from Cytochrome P450 (CYPs) superfamily. Pharmacogenetic studies search for genetic differences between populations since relevant alleles occur with varying frequencies among different ethnic populations. The Brazilian population is one of the most heterogeneous in the world, resulting from multiethnic admixture of Amerindians, Europeans, and Africans across centuries. Since the knowledge of CYP allele frequency distributions is relevant to pharmacogenetic strategies and these data are scarce in the Brazilian population, this study aimed to describe genotype and allele distributions of 15 single nucleotide polymorphisms (SNPs) at CYP 1A2, 2C19, 3A4, and 3A5 genes in African and European descents from South Brazil. A sample of 179 healthy individuals of European and African ancestry was genotyped by the MassARRAY SNP genotyping system. CYP3A5*3, CYP1A2*1F, CYP3A4*1B, and CYP2C19*2 were the most frequent alleles found in our sample. Significant differences in genotype and allelic distribution between African and European descents were observed for CYP3A4 and CYP3A5 genes. CYP3A4*1B was observed in higher frequency in African descents (0.379) than in European descents (0.098), and European descents showed higher frequency of CYP3A5*3 (0.810) than African descents (0.523). Our results indicate that only a few polymorphisms would have impact in pharmacogenetic testing in South Brazilians. Further studies with larger sample sizes are required also among other Brazilian regions.