Peptidehelicenes in solution and gel: chiral discrimination through interactions between two types of helixes

Helical [5]thiaheterohelicene 5HM, which rapidly interconverts between P and M enantiomers in solution, was connected to helical l-phenylalanine oligomers with an ester linkage to give peptidehelicenes (5Fn, where n: number of bonded phenylalanines). The characteristics of 5F4 and 5F5 with two types of helixes in a molecule were investigated, particularly in comparison with those of 5F1–5F3 with an incomplete coil of a peptide moiety. l-Phenylalanine peptide chains induced a shift in the equilibrium between the P and M helixes of 5HM toward the P side for all the 5Fns examined. The enantiomeric excess (ee) of the P form increased with a decrease in temperature, together with an elongation of the peptide chains. 5F4 and 5F5 in hot solutions of some solvents formed a gel at room temperature, whereas 5F1–5F3 showed no such behavior. In this gel, the stable helical form of the 5HM moiety in 5F4 and 5F5 was observed to be the M form in contrast to that in their solutions.     

Force field-SCF calculations on cyclopropene intermediates in carbene rearrangements. Comparison with experiment

Heats of formation and geometries of benzocyclopropene, cyclopropa[b]naphthalene, bicyclo[4.1.0]hepta-2,4,7-triene, and benzannelated derivatives have been calculated with a combined force field-SCF program. The bicycloheptatrienes are stabilized relative to the isomeric arylcarbenes by benzannelation, and destabilized by loss of aromaticity and/or increased strain. 1-Naphthylcarbene, 2-naphthylcarbene, 9-phenanthrylcarbene and 9-anthrylcarbene were generated by gas-phase pyrolysis of the corresponding arene aldehyde tosylhydrazone sodium salts, diazomethanes, or 5-aryltetrazoles, and rearranged to cyclobuta[de]naphthalene (21), cyclobuta[jk]phenanthrene (33), and cyclobuta[de] anthracene (38), respectively. 10,11-Dihydrodibenzo[ad]cyclohepten-5-ylidene (15), similarly generated from 5-diazo-10,11-dihydro-5H-dibenzo [ad]cycloheptene(39), rearranged to 5a,9b-dihydro-5H-benzo[3,4]cyclobut[1,2-a] indene(40), 5H-dibenzo[ad]cycloheptene(41), and 8,9-dihydro-4H-cyclopenta[def]phenanthrene(44).40 rearranged thermally to 41. The mechanisms of the rearrangements are discussed.     

Enantioselective hydrolysis of (RS)-2-fluoroarylacetonitriles using nitrilase from Arabidopsis thaliana

The enzymatic resolution of 2-fluoroarylacetonitriles (RS)-3 using nitrilase from the plant Arabidopsis thaliana is described. Racemic 2-fluoronitriles 3 are easily accessible from O-silylated aromatic cyanohydrins 2 by reaction with DAST. The nitriles (RS)-3 were hydrolysed with the nitrilase as a catalyst, not to the expected 2-fluoroarylacetic acids but to the corresponding (R)-2-fluoroarylacetamides (R)-5 as the main products. After optimization of reaction conditions (pH 9, 7°C), the enantiomeric excesses of (R)-5a,c and f (R=H, 3-Me, 3-OMe) could be improved to >99% by one recrystallization. The acid catalysed hydrolysis of (R)-5a,5c and 5f afforded the corresponding (R)-2-fluoroarylacetic acids (R)-4a,4c and 4f without racemization.     

Incorporation of 5-substituted uracil derivatives into nucleic acids—III : Synthesis of 5-substituted uracils derived from 5-acetyluracil

5-Acetyluracil (1) has been converted into 5-(bromoacetyl)-uracil (2) by an established procedure. Reduction of 2 with sodium borohydride gave 5-(2-hydroxyethyl)uracil (4) in low yield. Treatment of 5-vinyluracil (7), obtained from 1 by published methods, with 1 molecular proportion of bromine followed by heating to 100°, gave E-5-(2-bromovinyl)uracil (8). Reaction of 8 with potassium t-butoxide gave 5(7)H-furanol[2,3,d]pyrimidin-6-one (10) and upon reduction with sodium in liquid ammonia, 8 gave 5-ethyluracil (11). Compound 2 showed low antibacterial activity against Staphylocuccus aureus, Streptococcus faecalis and Escherichia coli in nutrient broth and in a medium containing only inorganic salts, glucose and thymine, appreciable activity (～ 6 μg/ml) against E. coli. Compound 2 was not incorporated into the DNA of E. coli.     

A general strategy for the formal synthesis of (−)-trans-kumausyne and total synthesis of (5R)-Hagen’s gland lactones from diacetone-d-glucose

A general strategy for the formal synthesis of (−)-trans-kumausyne 1 via the bicyclic lactone (3aR,5R,6aR)-4 and total synthesis of (5R)-Hagen’s gland lactones 2 and 3 via bicyclic lactone (3aR,5S,6aR)-5 starting from diacetone-d-glucose 6 is described. Syntheses of 4 and 5 were achieved by Wittig olefination–lactonization–Michael addition of the corresponding lactols 16 and 17, respectively.     

Asymmetric hydrolysis,esterfication catalyzed by esterases from porcine pancreas in the synthesis of both enantiomers of cyclopentanoid building blocks

The asymmetric synthesis of the cyclopentanoid building blocks 5 and ent-5 from the easily accessible meso-diacetates 4 and meso-diols 7, respectively by crude PPL and a carboxyl esterase from crude PPL is described. Enzymatic esterfication of 8 by crude PPL gave the cyclohexanoid monoacetate 9, whereas by hydrolysis of 10 the cyclobutenoid monoacetate 11 was obtained.     

New polycyclic tetramate macrolactams from marine-derived Streptomyces sp. SCSIO 40060

Polycyclic tetramate macrolactams (PTMs) are widely distributed in nature and are generated from a compact biosynthetic pathway. Bioinformatics analysis of the draft genome sequence of marine-derived Streptomyces sp. SCSIO 40060 revealed the presence of a putative PTM-encoding biosynthetic gene cluster (BGC). Comparison of this PTM BGC with those from the databank by genome mining suggests that Streptomyces sp. SCSIO 40060 should produce PTMs with a 5/6/5 type of carbocyclic ring. Subsequently, a 40-L scale of cultivation of Streptomyces sp. SCSIO 40060 led to the isolation and characterization of four known PTMS, ikarugamycin (1), epoxyikarugamycin (2), capsimycin (3), capsimycin C (4), and three new PTMs, hydroxyikarugamycins A–C (5–7). The planar structures of 5–7 were assigned by comprehensive spectroscopic analysis and the absolute configurations of 5 and 6 were unequivocally determined by X-ray diffraction analysis. The absolute structure of 7 was deduced by comparing ECD spectra of 5–7. Capsimycin (3) showed antimicrobial activity against methicillin-resistant Staphylococcus aureus with a MIC value of 16?μg/mL and displayed cytotoxicity against several cancer cell lines with IC₅₀ values ranging from 2.62 to 6.87?μM.     

Ouverture régiospécifique d'un oxirane preparé á partir du d-xylose par des carbanions soufres: Synthèse de c-nucleosides branches

Two methods using the readily accessible D-xylose have been developed for the synthesis of epoxides 4 and 5. The oxirane 5 was considered as a good intermediate for the preparation of 3'-C-substituted nucleosides. The crucial step for the synthesis of 32 is the regiospecific opening of the epoxide 5 using two carbanions, derived from either dithiane or bis(phenylthio)methane, followed by desulphurisation leading to 17. The exclusive opening of the epoxide in 5 was unequivocally established by ¹³CNMR spectroscopy.     

Total synthesis of (+) methyl β-d-vicenisaminide

The total synthesis of methyl β-d-vicenisaminide 1 has been achieved. In this approach, the synthesis of enantiomerically pure methyl (4R,5S)- and (4S,5R)-4-azido-5-hydroxy-2(E)-hexenoates 2 was established by enzymatic resolution of (±)-anti-5-acetoxy -4-azido-2(E)-hexenoate 4. Another stereogenic center was introduced by base-catalyzed intramolecular conjugate addition of a hemiacetal-derived alkoxide nucleophile obtained by the reaction of methyl (4S,5R)-N-4-tert-butoxycarbonyl-N-methylamino-5-hydroxyl-2(E)-hexenoate 8 and benzaldehyde in the presence of a base.     

Two approaches to the enantioselective synthesis of (4R)-(−)-4-hydroxymethyl-4-thiobutyro-1,4-lactone

Enantiomerically pure (4R)-4-hydroxymethyl-4-thiobutyro-1,4-lactone [(5R)-dihydro-5-(hydroxymethyl)-2(3H)-thiophenone (12)] and derivatives were synthesized by two enantiospecific sequences employing d-ribono-1,4-lactone (1) and l-glutamic acid (6) as chiral templates. The key step in the first approach was the SmI₂-promoted 2,3-deoxygenation of a 4-thio-l-lyxono-1,4-lactone derivative, prepared from 1. The other strategy, which starts from 6, involves the (5S)-dihydro-5-(p-tolylsulfonyloxymethyl)-2-(3H)-furanone (8) as chiral precursor. This was converted into a 4,5-thiirane derivative via the corresponding 4,5-epoxide. Regioselective opening of the thiirane ring by acetate followed by O-deacetylation gave 12 (40% overall yield from 8).     

Synthesis of ethyl and t-butyl (3R,5S)-dihydroxy-6-benzyloxy hexanoates via diastereo- and enantioselective microbial reduction

Previously we have demonstrated the reduction of ethyl diketoester 4 to the corresponding dihydroxy ester 6a by Acinetobacter sp. SC13874. Recently we screened more than 100 cultures for microbial reduction of both the ethyl and t-butyl diketoesters 4 and 5. Most yeast cultures showed a preference for reduction at the C-3 with low enantioselectivity. Among the three Acinetobacter strains screened, Acinetobacter sp. SC13874 reduced both compounds 4 and 5 to the corresponding (3R)- and (5S)-monohydroxy compounds. Monohydroxy compounds were isolated and their absolute configurations determined. (3R)- and (5S)-Monohydroxy compounds were reduced further to the corresponding dihydroxy esters 6a and 8a to provide alternate routes for the synthesis of compounds 14a and 16a, potential intermediates for the synthesis of HMG-CoA reductase inhibitors. Cell suspensions of Acinetobacter sp. SC13874 reduced the ethyl diketoester 4 to a mixture of desired syn and undesired anti diastereomers. The desired syn-(3R,5S)-dihydroxy ester 6a was obtained with an enantiomeric excess (ee) of 99% and a diastereomeric excess (de) of 63%. Cell suspensions reduced the t-butyl diketoester 5 to a mixture of mono- and dihydroxy esters with the dihydroxy ester showing an ee of 87% and de of 51% for the desired syn-(3R,5S)-dihydroxy ester 8a. Three different ketoreductases were purified to homogeneity, and their biochemical properties compared. Reductase I only catalyzes the reduction of ethyl diketoester 4 to its monohydroxy products 10 and 11, whereas reductase II catalyzes the formation of dihydroxy products 6 and 7 from monohydroxy substrates 10 and 11. A third reductase (III) was identified, which catalyzes the reduction of diketoester 4 to syn-(3R,5S)-dihydroxy ester 6a.     

Composés á structure imidazopyridinyl-arylpropénone,nouveaux agents anti-infectieux potentiels

This paper describes the design by juxtaposition of anti-infectious moieties, a series of hybrid imidazopyridinyl-arylpropenone compounds. These compounds (5a–y) were synthesized by a crotonization reaction of 1-(2-methylimidazo[1,2-a]pyridin-3-yl)ethanone (3) with benzaldehyde derivatives (4). Spectral determination of structure of those compounds was performed by NMR and ESI mass spectroscopy. From the screening of antiparasitic and antimicrobial activities, the compound 5q (IC₅₀ = 1.52 μM) was identified for possible development against a chloroquine-resistant strain of Plasmodium falciparum. The compounds 5n, 5s and 5w showed a veterinary interest due to their nematicidal activities (LC₁₀₀) against Haemonchus contortus from 7.1 to 1.5 nM. Against candidiasis, three other compounds (5e, 5g, 5v) inhibited drug-resistant strains of Candida albicans (MIQ = 1.25 to 0.31 μg). This study showed that the arylpropenone functional group vectorised by imidazopyridine could be considered as a new pharmacophore with potential anti-infectious activities.     

A diastereoselective C–C bond formation at C-5 of d-gulose. A convenient approach to (5S)-5-C-alkyl-β-l-lyxo-hexofuranoses

A flexible approach to the stereoselective synthesis of (5S)-5-C-methyl- and (5S)-5-C-ethyl-β-l-lyxo-hexofuranoses 15a, 22 starting from 1,2:5,6-di-O-isopropylidene-α-d-gulofuranose 3 as the source of chirality is described. The corresponding C-5 alkyl groups were introduced via a Wittig olefination followed by Pd/C-mediated hydrogenation of the conformationally restricted alkenes in a highly diastereoselective manner.     

Lipase-mediated kinetic resolution of cis-1,2-indandiol and the Ritter reaction of its mono-acetate

Lipase-mediated kinetic resolution of cis-1,2-indandiol 5 in the presence of lipase PS was examined. Enantiomerically enriched (1S,2R)-2-acetoxy-1-indanol 6a was obtained when cis-1,2-indandiol 5 was treated with one equivalent of vinyl acetate. Treatment of 5 with two equivalents of vinyl acetate furnished a mixture of (1R,2S)-2-acetoxy-1-indanol 6a and (1R,2S)-1-acetoxy-2-indanol 6b. A route to both enantiomers of 1 was also developed by using the enantiomerically enriched mono-acetate thus obtained.     

Synthesis of enantiomerically pure spiro-cyclopropane derivatives containing multichiral centers

A novel chiral source, 5-(R)-[(1R,2S,5R)-(−)-menthyloxy]-3-bromo-2(5H)-furanone (5a), was obtained in 46% yield with d.e.≥98% from the epimeric mixture of 5-(l-menthyloxy)-3-bromo-2(5H)-furanone (5a+5b) obtained via the bromination of an epimeric mixture of 5-(l-menthyloxy)-2(5H)-furanone (3a+3b) followed by the elimination of hydrogen bromide. The asymmetric reaction of 5a with a nucleophilic alcohol afforded enantiomerically pure spiro-cyclopropane derivatives containing four stereogenic centers, 9a–9e, in 50–68% yield with d.e.≥98%. The enantiomerically pure compounds 9a–9e were identified on the basis of their analytical data and spectroscopic data, such as [α]_D²⁰, UV, IR, ¹H NMR, ¹³C NMR, MS and elementary analysis. The absolute configuration of the chiral spiro-cyclopropane compound 9a was established by X-ray crystallography.     

Synthesis of (1R,4E,5S)-4-{[(E)-(azinyl)diazenyl]methylidene}-1,8,8-trimethyl-2-oxabicyclo[3.2.1]octan-3-ones and (1R,4R,5R)-4-([1,2,4]triazolo[4,3-x]azin-3-yl)-1,8,8-trimethyl-2-oxabicyclo[3.2.1]octan-3-ones

4-[(Heteroaryldiazenyl)methylidene] and 4-([1,2,4]triazolo[4,3-x]azin-3-yl) substituted (1R,5R)-4-1,8,8-trimethyl-2-oxabicyclo[3.2.1]octan-3-ones 6/6′ and 7/7′ were obtained in a one-pot transformation of the enamino lactone 2 with hydrazinoazines 3a–g followed by oxidation of the intermediate mixture of isomeric enehydrazines 4/4′ and hydrazones 5/5′ with lead tetraacetate. The oxidation selectivity was dependent on the ratio of isomeric intermediates 4/4′ and 5/5′. Treatment of 7b with lead tetraacetate led to α-acetoxylated compound 11, while bromination of 9b afforded a 1:1 mixture of α-bromination products 12 and 12′, which were separated by medium pressure liquid chromatography (MPLC). The structures of intermediates and products were confirmed by NMR and X-ray diffraction.     

A simple and practical access to enantiopure 2,3-diamino acid derivatives

Enantiomerically pure (4R,5R)- and (4S,5S)-2-imidazolines 5 were conveniently obtained on a gram scale. These can be converted into enantiopure (2R,3R)-2,3-diamino ester 6 or 2,3-diamino alcohol 7 by hydrolysis or reduction.     

Biocatalytic oxidation of thiophosphoryl compounds: a new chemo-enzymatic approach to enantiomeric insecticidal thionophosphates and their oxons

The biocatalytic oxidation of racemic O-S-dimethyl O-p-nitrophenyl phosphorodithioate 5 catalyzed by chloroperoxidase from Caldariomyces fumago resulted in the formation of the (?)-(S)-enantiomer of the corresponding oxon 4 and unoxidized substrate 5 with a (+)-(R)-configuration. Both compounds were obtained with very high enantiomeric excesses, 99.6% and 97%, respectively. The thionation reaction of the resulting (?)-(S)-oxon 4 with Lawesson’s reagent gave (?)-(S)-phosphorodithioate 5 with full stereoselectivity, while the oxidation of unreacted substrate (+)-(R)-5 with iodoxybenzene afforded oxon (+)-(R)-4 with 94.9% ee.     

Study on enantiomerically pure 2-substituted N,N-dialkyl-1-naphthamides: resolution,absolute stereochemistry,and application to desymmetrization of cyclic meso anhydrides

The axially chiral 2-substituted N,N-diisopropyl-1-naphthamides 1 and 2 were resolved by HPLC over a chiral stationary phase to provide enantiomerically pure atropisomers. The absolute stereochemistry of (−)-syn-1 was determined by X-ray crystallographic analysis of the corresponding (1S)-camphanic acid ester derivative. Desymmetrization of cyclic meso anhydrides 5a and 5b using (−)-syn-1 gave a single diastereomer in good yield.     

Fluorosulfonic acid induced ring opening of pinanones: pinane chirality in synthesis1

The acid-catalysed ring opening of a number of substituted nopinones to give 4-(2-propyl)cyclohex-2-enones is described. In an application of this reaction use has been made of pinane chirality in the synthesis of R-o-mentha-2,4-diene (13) by fluorosulfonic acid-catalysed rupture of cis-verbanone (8) to (4S,5R)- and (4R,5R)-5-methyl-4(2-propyl)cyclohex-2-enone (9 and 10) followed by reduction-elimination.