Asit K. Chakraborti

Perchloric acid adsorbed on silica gel as a new, highly efficient, and versatile catalyst for acetylation of phenols, thiols, alcohols, and amines

Perchloric acid adsorbed on silica gel efficiently catalyses acetylation of structurally diverse phenols, alcohols, thiols, and amines under solvent free conditions.

Degradation of phenanthrene by different bacteria: evidence for novel transformation sequences involving the formation of 1-naphthol.

Abstract Four polycyclic aromatic hydrocarbon (PAH)- degrading bacteria, namely Arthrobacter sulphureus RKJ4, Acidovorax delafieldii P4-1, Brevibacterium sp. HL4 and Pseudomonas sp. DLC-P11, capable of utilizing phenanthrene as the sole source of carbon and energy, were tested for its degradation using radiolabelled phenanthrene. [9-14C]Phenanthrene was incubated with microorganisms containing 100 mg/l unlabelled phenanthrene and the evolution of 14CO2 was monitored: within 18 h of incubation, 30.1, 35.6, 26.5 and 2.1% of the recovered radiolabelled carbon was degraded to 14CO2 by RKJ4, P4-1, HL4 and DLC-P11, respectively. When mixtures of other PAHs such as fluorene, fluoranthene and pyrene, in addition to phenanthrene, were added as additional carbon sources, there was a 36.1 and 20.6% increase in 14CO2 production from [9-14C]phenanthrene in the cases of RKJ4 and HL4, respectively, whereas P4-1 and DLC-P11 did not show any enhancement in 14CO2 production. Although, a combination of many bacteria enhances the degradation of organic compounds, no enhancement in the degradation of [9-14C]phenanthrene was observed in mixed culture involving all four microorganisms together. However, when different PAHs, as indicated above, were used in mixed culture, there was a 68.2% increase in 14CO2 production. In another experiment, the overall growth rate of P4-1 on phenanthrene could be enhanced by adding the non-ionic surfactant Triton X-100, whereas RKJ4, HL4 and DLC-P11 did not show any enhancement in growth. Pathways for phenanthrene degradation were also analysed by thin-layer chromatography, gas chromatography and gas chromatography-mass spectrometry. Common intermediates such as o-phthalic acid and protocatechuic acid were detected in the case of RKJ4 and o-phthalic acid was detected in the case of P4-1. A new intermediate, 1-naphthol, was detected in the cases of HL4 and DLC-P11. HL4 degrades phenanthrene via 1-hydroxy-2-naphthoic acid, 1-naphthol and salicylic acid, whereas DLC-P11 degrades phenanthrene via the formation of 1-hydroxy-2-naphthoic acid, 1-naphthol and o-phthalic acid. Both transformation sequences are novel and have not been previously reported in the literature. Mega plasmids were found to be present in RKJ4, HL4 and DLC-P11, but their involvement in phenanthrene degradation could not be established.

“On water” organic synthesis: a highly efficient and clean synthesis of 2-aryl/heteroaryl/styryl benzothiazoles and 2-alkyl/aryl alkyl benzothiazolines

A convenient and clean “on water”-mediated synthesis of benzothiazoles/benzothiazolines is reported. Aromatic, heteroaromatic, and styryl aldehydes are converted to 2-substituted benzothiazoles in high yields in a one-pot reaction with 2-aminothiophenol in water at 110 °C (oil-bath). Alkyl and aryl alkyl aldehydes afforded the benzothiazolines. The reaction is highly chemoselective with no competitive thia-Michael addition, O-dealkylation/debenzoylation, reduction of the nitro or the α,β-unsaturated carbonyl groups, and substitution of the halogen atom or the nitro group. The reaction is found to be general with respect to the 2-aminothiophenol substrate through the reaction of a few substituted 2-aminothiophenols with a few representative aromatic and aliphatic aldehydes. The procedure does not involve the use of any additional reagent/catalyst, produces no waste, and represents a green synthetic protocol.

Zirconium(IV) Compounds As Efficient Catalysts for Synthesis of α-Aminophosphonates

Zirconium(IV) compounds are reported as excellent catalysts for a three-component one-pot reaction of an amine, an aldehyde or a ketone, and a di/trialkyl/aryl phosphite to form alpha-aminophosphonates under solvent-free conditions at rt. Among the various zirconium compounds, ZrOCl2 x 8 H2O and ZrO(ClO4)2 x 6 H2O were most effective. The reactions were faster with dialkyl/diaryl phosphites than with trialkyl/triaryl phosphites. No O-Me cleavage occurs with aryl methyl ether and methyl ester groups. alpha,beta-Unsaturated carbonyl moiety does not undergo conjugate addition with the phorphorous moiety.

Indium(III) chloride as a new, highly efficient, and versatile catalyst for acylation of phenols, thiols, alcohols, and amines

Indium(III) chloride efficiently catalyses the acylation of structurally diverse phenols, alcohols, thiols, and amines under solvent free conditions. Acid sensitive alcohols are smoothly acylated without competitive side reactions. Acylation of 2-hydroxynaphthalene is carried out with carboxylic acids adopting the mixed anhydride protocol using trifluoroacetic anhydride.

Fluoroboric acid adsorbed on silica gel as a new and efficient catalyst for acylation of phenols, thiols, alcohols, and amines

Fluoroboric acid supported on silica gel efficiently catalyzes acylation of structurally diverse phenols, alcohols, thiols, and amines under solvent free conditions. Acid-sensitive alcohols are smoothly acylated without competitive side reactions.

Catalytic application of room temperature ionic liquids: [bmim][MeSO4] as a recyclable catalyst for synthesis of bis(indolyl)methanes. Ion-fishing by MALDI-TOF-TOF MS and MS/MS studies to probe the proposed mechanistic model of catalysis

The catalytic application of room temperature ionic liquids (RTILs) has been explored to catalyse the reaction of indole with aldehydes to afford bis(indolyl)methanes. The catalytic efficiency of the RTILs derived from butylmethylimidazolium (bmim) cation is influenced by the structure of the imidazolium moiety and the counter anion following the order: [bmim][MeSO4] > [bmim][HSO4] ≈ [bmim][MeSO3] ≫ [bmim][BF4] > [bmim][Br] > [bmim][NTf2] ≈ [bmim][PF6] > [bmim][N(CN)2] ≈ [bmim][ClO4] ≈ [bmim][HCO2] > [bmim][N3] > [bmim][OAc]. Substitution of the C-2 hydrogen in [bmim][MeSO4] decreased the catalytic efficiency. In the 1-methyl-3-alkylimidazolium methyl sulfates, the best results are obtained with the 3-butyl derivative and the catalytic property was retained with ethyl, n-propyl, and n-pentyl groups at N-3 although to a lesser extent with respect to the 3-butyl analogue. However, much reduction of the catalytic effect is observed with n-hexyl at N-3. The method is simple, environment friendly, compatible with various functional groups such as halogen, alkoxy, nitrile and O-t-Boc and gives excellent yields in short times. The catalyst is recyclable upto three consecutive uses. A mechanism has been proposed invoking ambiphilic dual activation role of the IL through the formation of intermediates involving hydrogen bond formation between the oxygen atom of the aldehyde carbonyl (or the transiently formed indolyl methanol in the subsequent step) and the C-2 hydrogen atom of the bmim cation, electrostatic intercation between the quarternary nitrogen atom of the bmim cation with the nitrogen lone pair of electrons of the indole and enforced hydrogen bond formation between the indole N–H hydrogen atom and the anion of the IL. The transient indolyl methanol and intermediate non-covalent clusters were “fished” by MALDI-TOF-TOF MS and MS/MS studies and served as ‘proof-of-concept’ to the mechanistic model.

Supramolecular Assemblies in Ionic Liquid Catalysis for Aza-Michael Reaction

Supramolecular assemblies formed by a relay of cooperative hydrogen bonds and charge-charge interactions have been identified/characterized by (+ve) ESI and MALDI-TOF-TOF MS and MS-MS studies during the aza-Michael reaction of amines with alpha,beta-unsaturated carbonyl compounds in the presence of ionic liquids (ILs) digging out the role of catalysis by ILs, forming the basis of rational design/selection as organocatalysts, and offering a diagnostic model to predict/rationalize the selectivity of the aza-Michael reaction in a competitive environment.

Progress in COX-2 Inhibitors: A Journey So Far

The non-steroidal anti-inflammatory drugs (NSAIDs) are diverse group of compounds used for the treatment of inflammation, since the introduction of acetylsalicylic acid in 1899. Traditional (first generation) NSAIDs exert antiinflammatory, analgesic, and antipyretic effects through the blockade of prostaglandin synthesis via non-selective inhibition of cyclooxygenase (COX-1 and COX-2) isozymes. Their use is associated with side effects such as gastrointestinal and renal toxicity. A number of selective (second generation) COX-2 inhibitors (rofecoxib, celecoxib, valdecoxib etc.) were developed as safer NSAIDs with improved gastric safety profile. Observation of increased cardiovascular risks in APPROVe (Adenomatous Polyp Prevention on Vioxx) study sent tremors and led to voluntary withdrawn of Vioxx (rofecoxib) by Merck from the market in September 2004 followed by Bextra (valdecoxib) in 2005 raising a question on the safety of selective COX-2 inhibitors. This leads to the belief that these effects are mechanism based and may be class effect. However, some studies suggested association of traditional NSAIDs with similar effects requiring a relook into the whole class of NSAIDs rather than simply victimizing the selective COX-2 inhibitors. Recognition of new avenues for selective COX-2 inhibitors such as cancer, Alzheimers disease, Parkinsons disease, schizophrenia, major depression, ischemic brain injury and diabetic peripheral nephropathy has kindled the interest in these compounds. This review highlights the various structural classes of selective COX-2 inhibitors developed during past seven years (2003-2009) with special emphasis on diaryl-hetero/carbo-cyclic class of compounds. Molecular modeling aspects are also briefly discussed.

Protic Acid Immobilized on Solid Support as an Extremely Efficient Recyclable Catalyst System for a Direct and Atom Economical Esterification of Carboxylic Acids with Alcohols

A convenient and clean procedure of esterification is reported by direct condensation of equimolar amounts of carboxylic acids with alcohols catalyzed by an easy to prepare catalyst system of perchloric acid immobilized on silica gel (HClO(4)-SiO(2)). The direct condensation of aryl, heteroaryl, styryl, aryl alkyl, alkyl, cycloalkyl, and long-chain aliphatic carboxylic acids with primary/secondary alkyl/cycloalkyl, allyl, propargyl, and long-chain aliphatic alcohols has been achieved to afford the corresponding esters in excellent yields. Chiral alcohol and N-t-Boc protected chiral amino acid also resulted in ester formation with the representative carboxylic acid or alcohol without competitive N-t-Boc deprotection and detrimental effect on the optical purity of the product demonstrating the mildness and chemoselectivity of the procedure. The esters of long-chain (>C(10)) acids and alcohols are obtained in high yields. The catalyst is recovered and recycled without significant loss of activity. The industrial application of the esterification process is demonstrated by the synthesis of prodrugs of ibuprofen and a few commercial flavoring agents. Other protic acids such as H(2)SO(4), HBr, TfOH, HBF(4), and TFA that were adsorbed on silica gel were less effective compared to HClO(4)-SiO(2) following the order HClO(4)-SiO(2) >> H(2)SO(4)-SiO(2) > HBr-SiO(2) > TfOH-SiO(2) >> HBF(4)-SiO(2) approximately TFA-SiO(2). When HClO(4) was immobilized on other solid supports the catalytic efficiency followed the order HClO(4)-SiO(2) > HClO(4)-K10 > HClO(4)-Al(2)O(3) (neutral) > HClO(4)-Al(2)O(3) (acidic) > HClO(4)-Al(2)O(3) (basic).