Effect of acyl chain length on selective biocatalytic deacylation on O-aryl glycosides and separation of anomers

It has been demonstrated that Lipozyme® TL IM (Thermomyces lanuginosus lipase immobilised on silica) can selectively deacylate the ester function involving the C-5' hydroxyl group of α-anomers over the other acyl functions of anomeric mixture of peracylated O-aryl α,β-D-ribofuranoside. The analysis of results of biocatalytic deacylation reaction revealed that the reaction time decreases with the increase in the acyl chain length from C1 to C4. The unique selectivity of Lipozyme® TL IM has been harnessed for the separation of anomeric mixture of peracylated O-aryl α,β-D-ribofuranosides, The lipase mediated selective deacylation methodology has been used for the synthesis of O-aryl α-D-ribofuranosides and O-aryl β-D-ribofuranosides in pure forms, which can be used as chromogenic substrate for the detection of pathogenic microbial parasites containing glycosidases.

Selective biocatalytic acylation studies on 5'-O-(4,4'-dimethoxytrityl)-2',3'-secouridine: an efficient synthesis of UNA monomer

Lipozyme(®) TL IM (Theremomyces lanuginosus lipase immobilized on silica) in toluene catalyzes the acylation of the 2'-OH over the 3'-OH group in 5'-O-(4,4'-dimethoxytrityl)-2',3'-secouridine (5'-O-DMT-2',3'-secouridine) in a highly selective fashion in moderate to almost quantitative yields. The turn over during benzoyl transfer reactions mediated by vinyl benzoate or benzoic anhydride was faster than in acyl transfer reactions with vinyl acetate or C(1) to C(5) acid anhydrides; except in the case of butanoic anhydride. The 2'-O-benzoyl-5'-O-DMT-2',3'-secouridine obtained by Lipozyme(®) TL IM catalyzed benzoylation of 5'-O-DMT-2',3'-secouridine was successfully converted into its 3'-O-phosphoramidite derivative in satisfactory yield, which is a building block for the preparation of oligonucleotides containing the uracil monomer of UNA (unlocked nucleic acid).

Ethyl 3',4',5'-trimethoxythionocinnamate modulates NF-κB and Nrf2 transcription factors

Recently, we identified a novel cinnamate analog, ethyl 3',4',5'-trimethoxythionocinnamate (ETMTC) as a potent inhibitor of cell adhesion molecules (CAMs), such as intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1) and E-selectin. However, its mechanism of action has not been elucidated so far. Since, nuclear factor-kappa B (NF-κB) is the major transcription factor involved in the regulation of ICAM-1, VCAM-1 and E-selectin expression, we determined the status of NF-κB activation in ETMTC treated human endothelial cells. Here, we demonstrate that ETMTC inhibits TNF-α-induced nuclear translocation and activation of NF-κB by inhibiting phosphorylation and degradation of IκBα. The inhibition of IκBα phosphorylation and degradation by ETMTC was found to be due to its ability to inhibit IκB kinase activity. In addition, oxidative stress is known to regulate NF-κB activation through TNF-α signaling cascade, therefore, we examined the effect of ETMTC on TNF-α-induced reactive oxygen species generation. We observed that ETMTC significantly inhibits TNF-α-induced reactive oxygen species generation in endothelial cells. To further elucidate the anti-oxidant potential of ETMTC, we examined its effect on induction of anti-oxidant genes viz. glutamate-cysteine ligase, modifier subunit (GCLM), heme oxygenase-1 (HO1) and NAD (P)H:quinone oxidoreductase 1 (NQO1) in human bronchial epithelial cells. Interestingly, ETMTC significantly induces the anti-oxidant genes viz. GCLM, HO1 and NQO1 by activating nuclear factor-erythroid 2 p45-related factor 2 (Nrf2). Thus, ETMTC could be useful towards developing potent anti-inflammatory molecules.

A novel cinnamate derivative attenuates asthma features and reduces bronchial epithelial injury in mouse model

Airway epithelial injury is the hallmark of various respiratory diseases and therapeutic targeting of epithelial injury could be an effective strategy for controlling these diseases. We recently reported that a novel cinnamate, ethyl 3',4',5'-trimethoxythionocinnamate (ETMTC) derived from Piper longum derivative, was most potent among various cinnamate derivatives in inhibiting inflammatory cell adhesion molecules (CAMs). In this study, we investigated the effects of ETMTC on the features of allergic asthma and epithelial injury in a murine model. ETMTC treatment to ovalbumin sensitized and challenged mice during ovalbumin challenge reduced airway hyperresponsiveness, and airway inflammation. This attenuation of asthma features was associated with the reduction in the expressions of various CAMs, NF-κB activation, Th2 cytokines, eotaxin and 8-isoprostane that were estimated in lung homogenates. Further, it increased activities of mitochondrial complexes I and IV in lung mitochondria and reduced cytochrome c and caspase 9 activities in lung cytosol. In addition, it reduced the levels of oxidative DNA damage marker in bronchoalveolar lavage fluid and DNA fragmentation of bronchial epithelia in lung sections. Further, ETMTC not only increased the levels of 15-(S)-hydroxyeicosatetraenoic acid, suppressor of airway remodeling, but also inhibited goblet cell metaplasia and sub-epithelial fibrosis. These results demonstrate that ETMTC reduces epithelial injury and mitochondrial dysfunction associated with allergic asthma and thus ETMTC could be useful to develop efficient therapeutic molecule against asthma.

Chemical constituents of the genus Prunus and their medicinal properties

Prunus is a genus of trees and shrubs, including the plums, cherries, peaches, apricots and almonds. Nearly five hundred seventy chemical compounds have so far been isolated from several Prunus species. This comprehensive review summarizes the isolation of chemical compounds reported during the period 1908 to June 2010. As per scrutiny of literature, we did not find any review on the chemistry or biology of genus Prunus or on the biological activities of its constituents. Extensive work has been done at the Department of Chemistry, University of Delhi by several groups on the isolation, identification, biological activity evaluation and synthesis of a large number of novel compounds from different Prunus species during the the last six decades (1940-2000), primarly by Seshadri, Nagarajan and Parmar et al. on P. domestica, P. cerasus, P. cerasoides, P. puddum and P. communis. This comprehensive review will benefit a large number of researchers in the fields of chemistry, botany, drug industries and pharmacology.

Coumarins as antioxidants

Coumarins, a well-known class of naturally occurring compounds, display a remarkable array of biochemical and pharmacological actions, some of which suggest that certain members of this group of compounds may significantly affect the function of various mammalian cellular systems. The development of coumarins as antioxidant agents has attracted much attention in recent years. Coumarins afford an opportunity for the discovery of new antioxidants with truly novel mechanisms of action. This review updates and expands the 2006 review by the same author. The review considers and incorporates the most recently published literature on coumarins as related to their antioxidant properties. A lot of coumarins have been identified from natural sources, especially green plants. These natural compounds have served as valuable leads for further design and synthesis of more active analogues. Beyond doubt, a deep understanding of the mechanisms of existing synthetic and natural coumarins will build the basis for the rational design.

Characterization of 7-amino-4-methylcoumarin as an effective antitubercular agent: structure-activity relationships

OBJECTIVES

The objective of the present study was to evaluate the antitubercular activity of amino and acyl amino derivatives of coumarins when used alone and in combination with isoniazid, rifampicin, streptomycin or ethambutol, and to decipher the mode of action of the most effective agent.

METHODS

A series of amino and acyl amino coumarins were synthesized and screened for activity against the Mycobacterium tuberculosis H37Rv strain. These compounds were further evaluated by standard assay procedures to determine their MBCs, fractional inhibitory concentration index values and cytotoxicities. The MICs for a susceptible and a multidrug-resistant clinical isolate of M. tuberculosis were also determined. Electron and fluorescence microscopy of the test compound-treated mycobacterial samples were also carried out in an attempt to find out the target of action.

RESULTS

7-Amino-4-methylcoumarin (7-amino-4-methyl-2H-chromen-2-one; NA5) displayed the lowest MIC of 1 mg/L against not only H37Rv but also the susceptible as well as the multidrug-resistant clinical isolates. Certain acyl amino coumarins were also found to inhibit the aforementioned strains and isolates with MICs in the range of 1.0-3.5 mg/L. They were also found to act in synergy with isoniazid/rifampicin. Electron microscopy revealed the cell-wall-attacking characteristic of these compounds, while fluorescence microscopy indicated that mycolic acid might be the target of action.

CONCLUSIONS

The present study clearly demonstrated the in vitro antitubercular potential of the novel drug candidate NA5. Further studies are warranted to establish the in vivo efficacy and therapeutic potential of NA5.

Biocatalytic route to sugar-PEG-based polymers for drug delivery applications

Sugar-PEG-based polymers were synthesized by enzymatic copolymerization of 4-C-hydroxymethyl-1,2-O-isopropylidene-β-L-threo-pentofuranose/4-C-hydroxymethyl-1,2-O-benzylidene-β-L-threo-pentofuranose/4-C-hydroxymethyl-1,2-O-isopropylidene-3-O-pentyl-β-L-threo-pentofuranose with PEG-600 dimethyl ester using Novozyme-435 (Candida antarctica lipase immobilized on polyacrylate). Carbohydrate monomers were obtained by the multistep synthesis starting from diacetone-D-glucose and PEG-600 dimethyl ester, which was in turn obtained by the esterification of the commercially available PEG-600 diacid. Aggregation studies on the copolymers revealed that in aqueous solution those polymers bearing the hydrophobic pentyl/benzylidene moiety spontaneously self-assembled into supramolecular aggregates. The critical aggregation concentration (CAC) of polymers was determined by surface tension measurements, and the precise size of the aggregates was obtained by dynamic light scattering. The polymeric aggregates were further explored for their drug encapsulation properties in buffered aqueous solution of pH 7.4 (37 °C) using nile red as a hydrophobic model compound by means of UV/vis and fluorescence spectroscopy. There was no significant encapsulation in polymer synthesized from 4-C-hydroxymethyl-1,2-O-isopropylidene-β-L-threo-pentofuranose because this sugar monomer does not contain a big hydrophobic moiety as the pentyl or the benzylidene moiety. Nile red release study was performed at pH 5.0 and 7.4 using fluorescence spectroscopy. The release of nile red from the polymer bearing benzylidene moiety and pentyl moiety was observed with a half life of 3.4 and 2.0 h, respectively at pH 5.0, whereas no release was found at pH 7.4.

Protein acyltransferase function of purified calreticulin: the exclusive role of P-domain in mediating protein acylation utilizing acyloxycoumarins and acetyl CoA as the acyl group donors

The distinct biochemical function of endoplasmic reticulum (ER) protein Calreticulin (CR) catalyzing the transfer of acyl group from acyloxycoumarin to a receptor protein was termed calreticulin transacylase (CRTAase). The present study, unlike the previous reports of others utilizing CR-deficient cells alone, dealt with the recombinant CR domains of Heamonchus contortus (rhCRTAase) in order to examine their CRTAase activity. P-domain of rhCR unlike N- and C-domains was found to be endowed with CRTAase function. We have also observed for the first time acetyl CoA, as a substrate for rhCRTAase/P-domain mediated acetylation of recombinant Schistosoma japonicum glutathione S-transferase (rGST). rhCRTAase/P-domain were also found to undergo autoacylation by acyloxycoumarins. Also, the isolated autoacylated rhCRTAase/P-domain in non-denatured form alone exhibited the ability to transfer acyl group to rGST indicating the stable intermediate nature of acylated CR. P-domain catalyzed acetylation of rGST by 7,8-Diacetoxy-4-methylcoumarin or acetyl CoA resulted in the modification of several lysine residues in common was evidenced by LC-MS/MS analysis. The putative site of the binding of acyloxycoumarins with CR was predicted by computational blind docking studies. The results showed the involvement of two lysine residues Lys-173 and Lys-174 present in P-domain for binding acyloxycoumarins and acetyl CoA thus highlighting that the active site for the CRTAase activity would reside in the P-domain of CR. Certain ER proteins are known to undergo acetylation under the physiological conditions involving acetyl CoA. These results demonstrating CRTAase mediated protein acetylation by acetyl CoA may hint at CR as the possible protein acetyltransferase of the ER lumen.

Characterization of a unique dihydropyrimidinone, ethyl 4-(4'-heptanoyloxyphenyl)-6-methyl-3,4-dihydropyrimidin-2-one-5-carboxylate, as an effective antithrombotic agent in a rat experimental model

OBJECTIVES

To evaluate the potential of a novel dihydropyrimidinone, ethyl 4-(4'-heptanoyloxyphenyl)-6-methyl-3,4-dihydropyrimidin-2-one-5-carboxylate (H-DHPM), as a calcium channel blocker, endowed with the ability to inhibit platelet aggregation effectively.

METHODS

In-vitro and in-vivo studies were conducted for the determination of antiplatelet activity using adenosine diphosphate (ADP), collagen or thrombin as inducers. Calcium channel blocking activity and nitric oxide synthase (NOS) activity were monitored. Lipopolysaccharide (LPS)-mediated prothrombotic conditions were developed in rats to study the efficacy of H-DHPM to suitably modulate the inflammatory mediators such as inducible NOS (iNOS) and tissue factor. The cGMP level and endothelial NOS (eNOS) expression were checked in aortic homogenate of LPS-challenged rats pretreated with H-DHPM. The effect of H-DHPM on FeCl(3) -induced thrombus formation in rats was examined.

KEY FINDINGS

The concentrations of H-DHPM required to give 50% inhibition (IC50) of in-vitro platelet aggregation induced by ADP, collagen or thrombin were 98.2±2.1, 74.5±2.3 and 180.7±3.4µm, respectively. H-DHPM at a dose of 52.0±0.02mg/kg (133µmol/kg) was found to optimally inhibit ADP-induced platelet aggregation in-vivo. The level of nitric oxide was found to be up to 9±0.08-fold in H-DHPM-treated platelets in-vitro and 8.2±0.05-fold in H-DHPM-pretreated rat platelets in-vivo compared with control. OH-DHPM, the parent compound was found to be ineffective both in-vitro and in-vivo. H-DHPM-pretreated rats were able to resist significantly the prothrombotic changes caused by LPS by blunting the expression of iNOS, tissue factor and diminishing the increased level of cGMP to normal. H-DHPM enhanced the eNOS expression in aorta of rats treated with LPS. H-DHPM displayed synergy with antiplatelet activity of aspirin even at lower doses. H-DHPM was found to inhibit the LPS-induced platelet aggregation in younger as well as older rats. H-DHPM exhibited the ability to markedly decrease FeCl(3) -induced thrombus formation in rats.

CONCLUSIONS

H-DHPM has the attributes of a promising potent antiplatelet candidate molecule that should attract further study. H-DHPM displayed antiplatelet activity both in vivo and in vitro, which was due partially by lowering the intraplatelet calcium concentration.