Arthrobacter sp.: a lipase of choice for the kinetic resolution of racemic arylazetidinone precursors of taxanoid side chains

The native strain of Arthrobacter sp. (MTCC 5125) bearing a lipase has been found to be the most effective in the kinetic resolution of racemic arylazetidinones for producing cis-(3R,4S)-3-acetoxy-1-(4-methoxyphenyl)-4-phenyl-2-azetidinone, cis-(3R,4S)-3-acetoxy-1-(4-methoxyphenyl)-4-(2-furanyl)-2-azetidinone, cis-(3R,4S)-3-acetoxy-1-(4-methoxyphenyl)-4-(2-thienyl)-2-azetidinone, and cis-3-acetoxy-4-(t-butyl)-2-azetidinone products. The resolved compounds, which were obtained in high enantiopurity are important intermediates of amino acid side chains of paclitaxel as well as a new generation of taxanoids. The use of co-solvents dramatically improved the resolution efficacy of the lipase.     

Synthesis of new pyrazole-1,2,3-triazole dyads

An efficient two step synthetic methodology of new 5(4)-aryl-4(5)-[3(5)-(2-hydroxyphenyl)-1H-pyrazol-5(3)-yl]-1H-1,2,3-triazole dyads was established. The reaction of (E)-2-styryl-4H-chromen-4-ones, used as building blocks, with sodium azide, gave 4(5)-aryl-5(4)-(chromon-2-yl)-1H-1,2,3-triazoles bearing either electron-donating or electron-withdrawing substituents in their styryl moiety which upon reaction with hydrazine hydrate afforded the expected pyrazoles in moderate to very good yields.     

Asymmetric synthesis of (+)-trachyspic acid

Aldol reaction of di-tert-butyl 4-(4-methoxybenzyloxy)-2-oxobutanoate with pent-4-enal using (S)-1-(3,5-bis(trifluoromethyl)phenyl)-3-(pyrrolidin-2-ylmethyl)thiourea hydrochloride as a catalyst, followed by Pinnick oxidation and tert-butyl esterification, gave (2S,3S)-di-tert-butyl 2-(2-(4-methoxybenzyloxy)ethyl)-3-allyl-2-hydroxysuccinate in high optical purity (85% ee), from which the total synthesis of (+)-trachyspic acid, a tumor cell heparanase inhibitor, was accomplished.     

Stereochemical aspects of the chemistry of 2-[trialkyl(aryl)silyloxy]alkyl-4-alkoxyalk-2-enylstannanes

2-tert-Butyldimethylsilyloxymethyl-4-(methoxymethoxy)pent-2-enyl(tributyl)stannane, prepared predominantly as the (Z)-isomer, is transmetallated by tin(IV) chloride to generate an allyltin trichloride which reacts with aldehydes with excellent stereocontrol in favour of (E)-1,5-syn-3-tert-butyldimethylsilyloxymethyl-5-(methoxymethoxy)alk-3-en-1-ols. These were taken through to 3-[(E)-2-(methoxymethoxy)-propylidenyl]-5-alkyl(aryl)tetrahydrofurans and used to prepare more complex 4-(methoxymethoxy)-pent-2-enylstannanes.     

Synthesis and conformational and configurational studies of diastereoisomeric O-protected 4-(arylsulfonimidoyl)butane-1,2,3-triols

Chiral sulfoximines have applications as transition-state mimicking enzyme inhibitors, as peptide isosteres and as chiral auxiliaries in synthesis. To access the required O-protected 4-(arylsulfonimidoyl)butane-1,2,3-triols, 4S,5S-di(hydroxymethyl)-2,2-dimethyl-1,3-dioxolane (prepared from diethyl R,R-tartrate) was converted into its monobenzyl ether. Mitsunobu-like coupling with thiophenols gave 4S,5R-4-(benzyloxymethyl)-2,2-dimethyl-5-(arylthiomethyl)-1,3-dioxolanes. Sulfoxidation and S-imination (trifluoroacetamide, iodosobenzene diacetate, rhodium acetate) proceeded without stereoselectivity, giving inseparable diastereomeric mixtures of 4S,5R,S(±)-4-(benzyloxymethyl)-2,2-dimethyl-5-(N-(trifluoroacetyl)arylsulfonimidoylmethyl)-1,3-dioxolanes. Removal of the trifluoroacetyl protection allowed chromatographic separation of the diastereomeric 4S,5R,S(±)-4-(benzyloxymethyl)-2,2-dimethyl-5-(arylsulfonimidoylmethyl)-1,3-dioxolanes. The configurations at sulfur were determined by X-ray crystallography and some analysis of the solution and solid-state conformations was carried out. The resulting O-protected 4-(arylsulfonimidoyl)butane-1,2,3-triols are of use in developing enzyme inhibitors.     

Synthesis of a d,d- and l,d-heptose-containing hexasaccharide corresponding to a structure from Haemophilus ducreyi lipopolysaccharides

The synthesis of a linear hexasaccharide, 2-(4-trifluoroacetamidophenyl)ethyl (β-d-galactopyranosyl)-(1→4)-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-(1→3)-(β-d-galactopyranosyl)-(1→4)-(d-glycero-α-d-manno-heptopyranosyl)-(1→6)-(β-d-glucopyranosyl)-(1→4)-l-glycero-α-d-manno-heptopyranoside, corresponding to a structure found in Haemophilus ducreyi LPS, is described. A Barbier reaction between benzyloxymethyl chloride and a properly protected 6-aldo-1-thio-mannopyranoside yielded both the d,d- and the l,d-heptopyranoside (2 and 3, ratio 2:3), which were separated and both used in the synthesis. p-Methoxybenzyl and chloroacetyl groups were employed as temporary protecting groups, selectively removed in the presence of the persistent benzyl, acetyl, benzoyl and isopropylidene groups by treatment with DDQ/H₂O and hydrazine dithiocarbonate, respectively. Thioglycosides were utilised as donors throughout using either NIS/TfOH or DMTST as promoters. The introduction of the spacer into thioglycoside 5 was high-yielding (95%) but with low stereoselectivity (α:β 5:3). All other glycosylations are completely stereoselective. The target hexasaccharide is obtained via a 3+3 block approach with the yield in the final NIS/TfOH-promoted coupling between an N,N-diacetyl-trisaccharide thioglycosyl donor 20 and a 4′′-OH trisaccharide acceptor 13 being 75%.     

Synthesis of trans-[Re(NO)2-(Ph2PCH2CH2PPh2)2][BF4], a formal dinitrosyl complex of rhenium(-I) and its protic denitrosylation. X-Ray structure of trans-[ReF(NO)-(Ph2PCH2CH2PPh2)2][BF4]

Treatment of a THF solution of trans-[ReCl(N₂)(dppe)₂] (dppe = Ph₂PCH₂CH₂PPh₂) with NO, in the presence of Tl[BF₄], forms trans-[Re(NO)₂(dppe)₂][BF₄], a rare formal 20-electron d⁸-rhenium nitrosyl complex which, by reaction with HX (X = BF₄, Cl or HSO₄), gives trans-[ReF(NO)(dppe)₂][BF₄] (2) (the X-ray structure of which is reported) or trans-[ReX(NO)(dppe)₂]X (3, X = Cl or HSO₄), respectively, as well as nitrous oxide.     

An investigation into the diastereoselective palladation of oxazoline appended cobalt metallocenes

The diastereoselective reactions of palladium acetate with (η⁵-(S)-2-(4-methylethyl)oxzazolinylcyclopentadienyl)(η⁴-tetraphenylcyclobutadiene)cobalt, which gives a planar chiral palladacycle with (_pR) configuration, and (η⁵-(S)-2-(4-dimethylethyl)oxzazolinylcyclopentadienyl)(η⁴-tetraphenylcyclobutadiene)cobalt, which results in the opposite (_pS) configuration, are shown to be a consequence of these reactions displaying thermodynamic and kinetic control, respectively.     

Synthesis,anti-inflammatory and analgesic activity of 2-[4-(substituted benzylideneamino)-5-(substituted phenoxymethyl)-4H-1,2,4-triazol-3-yl thio] acetic acid derivatives

The title compounds 3a–l have been synthesized by the reaction of thiocarbohydrazide with substituted phenoxy acetic acid to obtained substituted 1,2,4-triazoles (1). Compound 1 was treated with various substituted aromatic aldehydes which results in 4-(substituted benzylideneamino)-5-(substituted phenoxymethyl)-2H-1,2,4-triazol-3(4H)-thiones (2a–g), further 2a–g is converted to 2-[4-(substituted benzylideneamino)-5-(substituted phenoxymethyl)-4H-1,2,4-triazol-3-yl thio] acetic acid (3a–l) derivatives by the reaction with chloroacetic acid. All the newly synthesized compounds were evaluated for in vivo anti-inflammatory and analgesic activities. Among the series 2-[4-(2,4-dichlorobenzylideneamino)-5-(phenoxymethyl)-4H-1,2,4-triazol-3-yl thio] acetic acid (3d), 2-[4-(4-dichlorobenzylideneamino)-5-(phenoxymethyl)-4H-1,2,4-triazol-3-yl thio] acetic acid (3e), 2-[4-(2,4-dichlorobenzylideneamino)-5-[(2,4-dichlorophenoxy)methyl]-4H-1,2,4-triazol-3-yl thio] acetic acid (3j) and 2-[5-[(2,4-dichlorophenoxy)methyl)]-4-(4-chlorobenzylideneamino)-4H-1,2,4-triazol-3-yl thio] acetic acid (3k) showed significant anti-inflammatory activity with P < 0.001 (63.4%, 62.0%, 64.1% and 62.5% edema inhibition, respectively), as compared to the standard drug diclofenac (67.0%) after third hour respectively and also compounds 3j, 3k exhibited significant analgesic activity with P < 0.001 (55.9% and 54.9% protection, respectively) and less ulcerogenic activity as compared with standard drug aspirin (57.8%).     

Facile ionic liquid-mediated,three-component sequential reactions for the green,regio- and diastereoselective synthesis of furocoumarins

An environmentally friendly approach to the diastereoselective synthesis of trans-4-oxo-3-aryl-3,4-dihydro-2H-furo[3,2-c]coumarin-2-carbonitriles, trans-2-benzoyl-3-(aryl)-2H-furo[3,2-c]chromen-4(3H)-ones and trans-ethyl-4-oxo-3-(aryl)-3,4-dihydro-2H-furo[3,2-c]chromene-2-carboxylates in good yields is described. The method is based on the sequential multicomponent reactions of 4-hydroxycoumarin, aromatic aldehydes and in situ generated cyanomethylpyridinium, phenacylpyridinium/(2-ethoxy-2-oxoethyl)pyridinium ylides, in the presence of the ionic liquid [BMIm]OH, which functions both as a catalyst and the reaction medium.     

Bioinspired manganese complexes catalyzed epoxidation for the synthesis of the epoxyketone fragment of carfilzomib

We report herein an efficient catalytic epoxidation reaction for the synthesis of epoxyketone (tert-butyl ((S)-4-methyl-1-((R)-2-methyloxiran-2-yl)-1-oxopentan-2-yl)carbamate), which is an important synthetic intermediate of carfilzomib.     

A novel synthesis of new 2-aryl-6-(arylamino)-1H-imidazo[1,2-b]pyrazole-7-carbonitrile derivatives

New 2-aryl-6-(arylamino)-1H-imidazo[1,2-b]pyrazole-7-carbonitriles are synthesized in good yields, via cyclocondensation of 5-amino-1-(2-oxo-2-arylethyl)-3-(arylamino)-1H-pyrazole-4-carbonitriles, which are prepared by the reaction of 5-amino-3-arylamino-1H-pyrazole-4-carbonitriles and α-bromoacetophenone derivatives in the presence of K₂CO₃ using acetone as the solvent.     

Synthesis of both enantiomers of baclofen using (R)- and (S)-N-phenylpantolactam as chiral auxiliaries

Esterification of racemic 4-nitro-3-(4-chlorophenyl)butanoic acid with (R)- or (S)-N-phenylpantolactam as the chiral auxiliary allowed us to obtain the (3R,3′R)- or (3S,3′S)-nitro esters with >98:2 dr after column chromatography. Hydrolysis of the resulting diastereopure nitro esters gave the corresponding enantiopure nitro acids, which were readily converted in high yields into either (R)- or (S)-baclofen hydrochloride.     

Synthesis and biological evaluation of N-thia-carba-thymidine as an antiherpetic agent

As a continuation of our project aimed at the search for new antiviral agents, the synthesis and biological evaluation of N-thia-carba-thymidine ((1R,2S,4S,5S)-5-methyl-1-{6-thia-4-hydroxy-5-[(hydroxy)-methyl]bicyclo[3.1.0]hex-2-yl}-1,3-dihydropyrimidine-2,4-dione; compound 8) was carried out employing the carbocyclic enantioenriched intermediate (1R,4S)-4-phenylmethoxy-3-[(phenylmethoxy)methyl]cyclopent-2-en-1-ol, which in turn was prepared from (3R,4S) phenylmethoxy-3-[(phenylmethoxy)methyl]-cyclopent-1-ene. The title compound resulted to be a very potent antiherpetic agent exhibiting a similar potency to acyclovir as shown. The synthetic approach to obtain this carbanucleoside required a novel strategy to introduce a thiirane group fused to a functionalized five-membered ring.     

Asymmetric synthesis of (+)-abresoline

The first asymmetric synthesis of (+)-abresoline has been achieved starting from the (S)-1-(aryl)homoallylic amine, which was prepared enantioselectively by the method based on allylation of the (R)-2′-(2-naphthyl)-bearing hydroxyoxime ether. This synthetic route employs the TiCl₄-induced intramolecular Mannich-type cyclization of the 1-azadiene-bearing ketal amine as the key steps to afford stereoselectively the cis-2,6-disubstituted piperidine, followed by CBr₄/PPh₃-induced dehydrocyclization for the elaboration of the amino alcohol to the trans-4-arylquinolizidine.     

Synthesis and Characterization of Novel Methyl (3)5-(N-Boc-piperidinyl)-1H-pyrazole-4-carboxylates

Series of methyl 3- and 5-(N-Boc-piperidinyl)-1H-pyrazole-4-carboxylates were developed and regioselectively synthesized as novel heterocyclic amino acids in their N-Boc protected ester form for achiral and chiral building blocks. In the first stage of the synthesis, piperidine-4-carboxylic and (R)- and (S)-piperidine-3-carboxylic acids were converted to the corresponding β-keto esters, which were then treated with N,N-dimethylformamide dimethyl acetal. The subsequent reaction of β-enamine diketones with various N-mono-substituted hydrazines afforded the target 5-(N-Boc-piperidinyl)-1H-pyrazole-4-carboxylates as major products, and tautomeric NH-pyrazoles prepared from hydrazine hydrate were further N-alkylated with alkyl halides to give 3-(N-Boc-piperidinyl)-1H-pyrazole-4-carboxylates. The structures of the novel heterocyclic compounds were confirmed by ¹H-, ¹³C-, and ¹⁵N-NMR spectroscopy and HRMS investigation.     

Asymmetric syntheses of 3,4-syn- and 3,4-anti-3-substituted-4-aminopiperidin-2-ones: application to the asymmetric synthesis of (+)-(3S,4R)-cisapride

The conjugate addition of lithium (R)-N-benzyl-N-(α-methylbenzyl)amide to δ-(N-allylamino)-α,β-unsaturated esters, followed by N-deallylation and cyclisation of the resultant β,δ-diamino esters, gives the corresponding 4-aminopiperidin-2-ones as single diastereoisomers (>99:1 dr). Subsequent deprotonation with LiHMDS and functionalisation of the resultant lithium enolate gives 3,4-anti-3-substituted-4-aminopiperidin-2-ones in >99:1 dr. Alternatively, in situ oxidation of the intermediate lithium (Z)-β-amino enolates formed upon conjugate addition gives α-hydroxy-β,δ-diamino esters, which after N-deallylation and cyclisation gives the corresponding 3,4-syn-3-hydroxy-4-aminopiperidin-2-ones in >99:1 dr. The utility of this methodology was successfully demonstrated in a concise asymmetric synthesis of the gastroprokinetic agent (+)-(3S,4R)-cisapride {(+)-(3S,4R)-N(1)-[3′-(4″-fluorophenoxy)propyl]-3-methoxy-4-(2?-methoxy-4?-amino-5?-chlorobenzamido)piperidine} in nine steps from commercially available starting materials with an overall yield of 19%.     

anti-Markovnikov addition of tellurium tetrachloride to trimethyl ethynyl silane

An investigation of the TeCl₄ interaction with trimethyl ethynyl silane 1 in CHCl₃ has shown that anti-Markovnikov adduct [Z-1-(trimethylsilyl)-2-chlorovinyl]tellurium trichloride is formed as the only product. In time, it is hydrolyzed to give [Z-1-(trimethylsilyl)-2-chlorovinyl]tellurium (hydroxy) dichloride which, in turn, is dehydrated to afford bis[(2-chloro-1-trimethyl-silylvinyl)dichlorotellurium]oxide. These data revealed that the reaction studied was the first example of anti-Markovnikov syn-addition of TeCl₄ to terminal acetylenes. A computed simulation of the TeCl₄ interaction with ethynyl silane 1 in a gas state using PES method did not reveal dominating orientation of the addition but showed the conditions at which anti-Markovnikov addition can occur and which were probably met in carrying out the reaction in CHCl₃.     

New developments in the Pd-catalysed cyclisation-coupling reaction of alkene-containing carbonucleophiles with organic halides (and triflates). The first examples of asymmetric catalysis.

The results of our preliminary investigations directed toward asymmetric catalysis of the cyclocarbopalladation of alkenes bearing a proximate nucleophile with organic halides (or triflates) are disclosed. A series of bidentate phosphine ligands were evaluated in intramolecular versions of this reaction using (E)-2-[7-(2-bromophenyl)-hept-4-enyl]-malonic acid dimethyl ester (1) and (Z)-2-[7-(2-trifluoromethanesulfonyloxy-phenyl)-hept-4-enyl]-malonic acid dimethyl ester (9) as model substrates. The highest enantioselective induction was obtained with aryl triflate 9 which produced the corresponding cyclopentylindane as a single diastereomer in 54% chemical yield and 43% ee by using PdCl₂[S-(−)-TolBINAP] as chiral catalyst and K₂CO₃ as base.     

Synthesis,Structure and Cytotoxicity Testing of Novel 7-(4,5-Dihydro-1H-imidazol-2-yl)-2-aryl-6,7-dihydro-2H-imidazo[2,1-c][1,2,4]triazol-3(5H)-Imine Derivatives

The appropriate 1-arylhydrazinecarbonitriles 1a–c are subjected to the reaction with 2-chloro-4,5-dihydro-1H-imidazole (2), yielding 7-(4,5-dihydro-1H-imidazol-2-yl)-2-aryl-6,7-dihydro-2H-imidazo[2,1-c][1,2,4]triazol-3(5H)-imines 3a–c, which are subsequently converted into the corresponding amides 4a–e, 8a–c, sulfonamides 5a–n, 9, ureas 6a–I, and thioureas 7a–d. The structures of the newly prepared derivatives 3a–c, 4a–e, 5a–n, 6a–i, 7a–d, 8a–c, and 9 are confirmed by IR, NMR spectroscopic data, as well as single-crystal X-ray analyses of 5e and 8c. The in vitro cytotoxic potency of these compounds is determined on a panel of human cancer cell lines, and the relationships between structure and antitumor activity are discussed. The most active 4-chloro-N-(2-(4-chlorophenyl)-7-(4,5-dihydro-1H-imidazol-2-yl)-6,7-dihydro-2H-imidazo[2,1-c][1,2,4]triazol-3(5H)-ylidene)benzamide (4e) and N-(7-(4,5-dihydro-1H-imidazol-2-yl)-2-(p-tolyl)-6,7-dihydro-2H-imidazo[2,1-c][1,2,4]triazol-3(5H)-ylidene)-[1,1′-biphenyl]-4-sulfonamide (5l) inhibits the growth of the cervical cancer SISO and bladder cancer RT-112 cell lines with IC₅₀ values in the range of 2.38–3.77 μM. Moreover, N-(7-(4,5-dihydro-1H-imidazol-2-yl)-2-phenyl-6,7-dihydro-2H-imidazo[2,1-c][1,2,4]triazol-3(5H)-ylidene)-4-phenoxybenzenesulfonamide (5m) has the best selectivity towards the SISO cell line and induces apoptosis in this cell line.