Synthesis and evaluation of novel 4-[(3H,3aH,6aH)-3-phenyl)-4,6-dioxo-2-phenyldihydro-2H-pyrrolo[3,4-d]isoxazol-5(3H,6H,6aH)-yl]benzoic acid derivatives as potent acetylcholinesterase inhibitors and anti-amnestic agents

The present study was designed to synthesize and evaluate pyrrolo-isoxazole benzoic acid derivatives as potential acetylcholinesterase (AChE) inhibitors for the management of Alzheimer's disease. The synthesis of pyrrolo-isoxazole benzoic acid derivatives involved ring opening cyclization of p-aminobenzoic acid with maleic anhydride to yield maleanilic acid, which in turn afforded N-arylmaleimide via ring closed cyclization. Azomethine-N-oxides were obtained by condensation of N-arylhydroxylamine with differently substituted benzaldehydes followed by refluxing of N-arylmaleimide with differently substituted azomethine-N-oxides to pyrrolo-isoxazole benzoic acid derivatives as cis- and trans-stereoisomers. The synthesized compounds were evaluated in vitro for AChE inhibitory activity in rat brain homogenate with donepezil as standard AChE inhibitor. Thereafter, the most potent test compound was evaluated for in vitro butyrylcholinesterase inhibitory activity and in vivo memory evaluation in scopolamine (0.4mg/kg)-induced amnesia in mice by employing Morris water maze test. All pyrrolo-isoxazole benzoic acid derivatives demonstrated potent AChE inhibitory activity. Most of compounds exhibited similar activity to donepezil and four of them (7h, 7i, 8i, and 8h, IC(50)=19.1±1.9-17.5±1.5nM) displayed higher inhibitory activity as compared to donepezil (21.5±3.2nM) with compound 8ia (IC(50)=17.5±1.5nM) being the most active one. The test compound 8ia also ameliorated scopolamine-induced amnesia in mice in terms of restoration of time spent in target quadrant (TSTQ) and escape latency time (ELT). It may be concluded that pyrrolo-isoxazole benzoic acid derivatives may be employed as potential AChE inhibitors.     

De novo asymmetric syntheses of C-4-substituted sugars via an iterative dihydroxylation strategy

A short and highly efficient route to various C-4 substituted sugar lactones has been developed. The key to the overall transformation is the sequential osmium-catalyzed dihydroxylation reaction of substituted 2,4-dienoates and an allylic substitution at the C-4 position. When the Sharpless AD-mix procedure is used in a matched sense for the second dihydroxylation reaction, it results in an exceedingly diastereo- and enantioselective synthesis of several C-4-substituted sugars.     

Development of environmentally friendly syntheses: use of enzymes and biomimetic systems for the direct carboxylation of organic substrates

Carboxylation reactions widely occur in nature by the direct use of carbon dioxide or hydrogen carbonate and are mediated by enzymes, which may or may not have a metal as an active center. Such direct carboxylation reactions have found only very few applications for synthetic purposes at industrial level. In this paper we review a part of the work we have done on the use of carbon dioxide and describe: (i) the use of a carboxylation enzyme for the conversion of phenol into 4-OH benzoic acid; and (ii) the potential of biomimetic mixed anhydrides for the synthesis of compounds of industrial interest. The enzymatic production of acetic acid from carbon dioxide is compared with known and new transition metal catalyzed reactions that are fully biomimetic.     

Studies on synthetic and structural characterization of new fluorine substituted phthalides of pharmaceutical interest

An efficient and economical synthesis of some new fluorine substituted phthalides was accomplished from two γ-keto acids, 2-(4-fluorobenzoyl)benzoic acid and 2-(3,5-dinitro-4-flurobenzoyl)benzoic acid. Each acid was reacted with various phenolic compounds in presence of catalytic quantity of concentrated sulphuric acid to get the phthalides. The structures of the synthesized compounds were established on the basis of their elemental analysis, spectral data and chemical reactions. Some of the synthesized phthalides exhibited antibacterial and antifungal activity on antimicrobial screening against human pathogenic bacteria and fungi.     

Studies on synthetic and structural characterization of new fluorine substituted phthalides of pharmaceutical interest

An efficient and economical synthesis of some new fluorine substituted phthalides was accomplished from two γ-keto acids, 2-(4-fluorobenzoyl)benzoic acid and 2-(3,5-dinitro-4-flurobenzoyl)benzoic acid. Each acid was reacted with various phenolic compounds in presence of catalytic quantity of concentrated sulphuric acid to get the phthalides. The structures of the synthesized compounds were established on the basis of their elemental analysis, spectral data and chemical reactions. Some of the synthesized phthalides exhibited antibacterial and antifungal activity on antimicrobial screening against human pathogenic bacteria and fungi.     

Drawbacks in the use of unconventional hydrophobic anhydrides for histone derivatization in bottom‐up proteomics PTM analysis

MS‐based proteomics has become the most utilized tool to characterize histone PTMs. Since histones are highly enriched in lysine and arginine residues, lysine derivatization has been developed to prevent the generation of short peptides (<6 residues) during trypsin digestion. One of the most adopted protocols applies propionic anhydride for derivatization. However, the propionyl group is not sufficiently hydrophobic to fully retain the shortest histone peptides in RP LC, and such procedure also hampers the discovery of natural propionylation events. In this work we tested 12 commercially available anhydrides, selected based on their safety and hydrophobicity. Performance was evaluated in terms of yield of the reaction, MS/MS fragmentation efficiency, and drift in retention time using the following samples: (i) a synthetic unmodified histone H3 tail, (ii) synthetic modified histone peptides, and (iii) a histone extract from cell lysate. Results highlighted that seven of the selected anhydrides increased peptide retention time as compared to propionic, and several anhydrides such as benzoic and valeric led to high MS/MS spectra quality. However, propionic anhydride derivatization still resulted, in our opinion, as the best protocol to achieve high MS sensitivity and even ionization efficiency among the analyzed peptides.     

Synthesis and biological evaluation of optically active conjugated γ- and δ-lactone derivatives

An efficient synthesis of racemic and both enantiomeric forms of heteroaryl substituted γ- and δ-lactone derivatives derived from allyl and homoallyl alcohol backbones has been accomplished via ring closing metathesis reaction. 2-Heteroaryl substituted allyl and homoallyl alcohols have been efficiently resolved through enzymatic method with high ee (97-99%) and known stereochemistry. Antimicrobial and antioxidant activities of target lactones were evaluated.     

Synthesis of buprestins D,E, F,G and H; structural confirmation and biological testing of acyl glucoses from jewel beetles (Coleoptera: Buprestidae)

A chemical and enzymatic synthesis was developed for five variant buprestins termed D, E, F, G and H found in jewel beetles (Coleoptera: Buprestidae). Selective acylation of the primary hydroxyl group of β-d-glucopyranose-1,2-bis(pyrrole-2-carboxylate) with substituted benzoic or cinnamic acid derivatives followed by deprotection gave the target compounds. Using coinjection the identity with the natural extracts was confirmed. The activity of the variant buprestins as deterrents for ants was assayed.     

Further sesquiterpene lactones from the genus Dittrichia

The aerial parts of Dittrichia graveolens afforded in addition to compounds isolated previously five new sesquiterpene lactones, two benzoic acid derivatives while D. viscosa gave two further derivatives of costic acid. The structures were elucidated by high field NMR spectroscopy.     

Iodine-catalyzed one-pot synthesis and antimalarial activity evaluation of symmetrically and asymmetrically substituted 3,6-diphenyl[1,2,4,5]tetraoxanes

A novel iodine-catalyzed one-pot synthesis of symmetrically and asymmetrically substituted 3,6-diphenyl-[1,2,4,5]tetraoxanes is described. The synthetic protocol is general with substituted benzaldehydes and proceeds well under acidic conditions. Total 17 tetraoxanes have been prepared during this study and some of these compounds exhibit promising antimalarial activity. None of the compounds shows any toxicity against vero cells.     

Aqueous Extract of the Pericarp of Sapindus trifoliatus Fruits: A Novel ‘Green’ Catalyst for the Aldimine Synthesis

The catalytic efficiency in organic synthesis of the aqueous extract of the pericarp of Sapindus trifoliatus fruits was evaluated. The synthesis of a series of aldimines from aromatic aldehydes and amines was successfully catalyzed by the extract, whereas aromatic ketones and amines did not yield ketimines under comparable reaction conditions, indicating the chemoselective catalysis of the extract. The catalytic activity of the extract is due to saponins, which have a common structural skeleton containing a pentacyclic triterpenoid part substituted with different carbohydrate side chains. The mild conditions, high yields, and short reaction times not only make this protocol a valuable alternative to the conventional methods, but it also becomes significant under the roof of environmentally greener and safer processes.     

An efficient synthesis of anhydrides of 2-monosubstituted succinic acid monoesters and their application to the Dakin–West reaction: Isolation of some 5-succinyloxyoxazole intermediates

A rapid and versatile synthesis of 2-monosubstituted monosuccinates and their bimolecular anhydrides is described. The reaction of these anhydrides with N-Fmoc-protected dipeptides under the modified Dakin–West reaction affords mainly the corresponding 5-succinyloxyoxazoles.     

Arabidopsis Chy1 null mutants are deficient in benzoic acid-containing glucosinolates in the seeds

The specific set of reactions that lead to the synthesis of benzoic acid in plants is still unclear, and even the subcellular compartment in which these reactions occur is unknown. Biosynthesis of both vegetative tissues and seeds of Arabidopsis thaliana contain a class of defense compounds termed glucosinolates, but only the seeds synthesize and store high levels of two glucosinolate compounds that contain a benzoic acid moiety. To identify genes involved in the synthesis of benzoic acid (directly or via benzaldehyde) in Arabidopsis , we analysed the levels of benzoylated glucosinolates in several lines that carry mutations in genes with homology to Pseudomonas fluorescens feruloyl-CoA hydratase, an enzyme that converts feruloyl-CoA to vanillin and acetyl-CoA, a reaction analogous to the conversion of cinnamoyl-CoA to benzaldehyde. We show here that mutations in the gene At5g65940 , previously shown to encode a peroxisomal protein with β-hydroxyisobutyryl-CoA hydrolase activity and designated as Chy1 , lead to a deficiency of benzoic acid-containing glucosinolates in the seeds. Furthermore, Chy1 exhibits cinnamoyl-CoA hydrolase activity with a K_m of 2.9 μ m . Our findings suggest that at least a part of benzoic acid biosynthesis occurs in the peroxisomes, although the specific pathway that leads to benzoic acid and the specific biochemical role of Chy1 remain unclear.     

An efficient synthesis of anhydrides of 2-monosubstituted succinic acid monoesters and their application to the Dakin–West reaction: Isolation of some 5-succinyloxyoxazole intermediates

Summary A rapid and versatile synthesis of 2-monosubstituted monosuccinates and their bimolecular anhydrides is described. The reaction of these anhydrides withN-Fmoc-protected dipeptides under the modified Dakin-West reaction affords mainly the corresponding 5-succinyloxyoxazoles.     

Synthesis of the food flavoring methyl benzoate by genetically engineered Saccharomyces cerevisiae

Current means of production for plant-derived aroma compounds include chemical synthesis and extraction from plant material. Both methods are environmentally detrimental and relatively expensive: plant material is only seasonally available and only a small subset of the plant biomass produces the desired aroma compounds, while organic synthesis inevitably involves waste byproducts with a negative ecological impact. Benzenoids are a class of plant metabolites that includes a number of aroma compounds. This paper explores, for the first time, the feasibility of producing benzenoids in yeast. We present a method for the production of the phenylpropanoid methyl benzoate in Saccharomyces cerevisiae using benzoic acid as a substrate, by heterologous expression of Antirrhinum majus benzoic acid methyl transferase. Production was pH dependent with a maximal yield of approximately 50 microg of methyl benzoate per liter of culture per hour, and with linear kinetics over at least 24 h. In addition, we have analyzed two alternative expression vectors for the production of benzoic acid methyl transferase in S. cerevisiae: a constitutive triosephosphate isomerase promoter-based system was compared with a copper-inducible CUP1 promoter system. We find major differences in the amounts of methylbenzoate produced by these respective systems. Potential applications are discussed.     

Microwave assisted solid support synthesis of novel 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazepines as potent antimicrobial agents

An environmentally benign and economic synthesis of 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazepines is described from readily accessible substituted 2-mercapto-1-amino triazoles and substituted chalcones on basic alumina that are accelerated by exposure to microwaves. The reaction time has been brought down from hours to seconds with improved yield as compared to conventional heating. The method reported herein is devoid of the hazards of solution phase reactions. All the synthesised compounds were tested for their in vitro antibacterial and antifungal activity. Some compounds showed significant antimicrobial properties. The best activity was observed with compounds 3a, 3c, 4a and 4d.     

Lactones of methyl 3-O

Lactones of methyl 3-O-[(R)- and (S)-1-carboxyethyl]-alpha-D-gluco-, galacto- and manno-pyranoside were prepared by treatment of the sugar derivatives in acetic acid. The lactones were formed between the 1-carboxyethyl substituent and 2-OH or 4-OH in different proportions depending on the stereochemistry of the parent compounds. Relative formation rates in acetic acid-d4 and hydrolysis rates in buffered D2O solutions at pD 2.4, 4.6 and 7.4 were estimated. Hydrolysis of the formed lactones is relatively slow in D2O at pD 4.6, which permitted characterization of the lactones by 1H and 13C NMR spectroscopy in buffered D2O solutions. Hydrolysis of the lactones in 1 M aqueous NaOH at 80 degrees C gave no detectable isomerization of the alpha-carbon. The set of lactones formed from the 1-carboxyethyl substituted methyl glycosides used in this study showed large similarities in the NMR shifts (delta delta values). Deviations from the observed shift pattern were found for two lactones. Our findings strongly suggest that those two lactones differ from the rest by adopting a boat-like conformation, whereas the others adopt pseudo-chair conformations.     

New entry to the enantioselective formation of substituted cyclohexenes bearing an all-carbon quaternary stereogenic center

Enantioselective formation of cyclohexene derivatives bearing an all-carbon quaternary stereogenic center is described. The racemic cyclohexenes are readily transformed to chiral substituted cyclohexenes in good yield with excellent enantioselectivity and diastereoselectivity by a palladium-mediated deracemization. The resulting products are promising synthetic intermediates of biologically active natural products. This protocol provides us with a new entry to the concise and scalable synthesis of multifunctionalized compounds.     

Macrolactones and polyesters from ricinoleic acid

A systematic study on the synthesis, characterization, and polymerization of ricinoleic acid (RA) lactone is reported. Ricinoleic acid lactones were synthesized by refluxing pure ricinoleic acid in chloroform (10 mg/mL) with dicyclohexylcarbodimide and (dimethylamino)pyridine as catalyst. Purification of RA lactones was performed by silica gel chromatography. The reaction resulted in a 75% yield of ricinoleic acid lactones. IR and NMR analysis confirmed the formation of cyclic compounds. Polymerization of the ricinoleic acid lactones with catalysts commonly used for ring-opening polymerization of lactones, under specific reaction conditions, resulted in oligomers. Copolymerization with lactide (LA) by ring-opening polymerization, using Sn(Oct) as catalyst, yielded copolyesters with molecular weights (M(w)) in the range of 5000-16000 and melting temperatures of 100-130 degrees C for copolymers containing 10-50% w/w ricinoleic acid residues. Degradation studies of the copolymers were performed in 0.1 M phosphate buffer solution, pH 7.4, at 37 degrees C. P(LA-RA)s with up to 20% w/w RA slowly degraded and released only approximately 7% of its lactic acid content after 60 days of study, while pure PLA under similar conditions released more than 20% of its lactic acid content. On the other hand, copolyesters containing more then 20% w/w RA degraded and released lactic acid faster than pure PLA due to the low crystallinity of the copolymers.