Isostructurality in crystalline oxa-androgens: a case of C-O-···O and C-H···O interaction mimicry and solid solution formation

A C-H···O interaction in 2-oxa-4-androstene-3,17-dione is replaced by a C-O-H···O hydrogen bond in the isostructural 6a-hydroxy analogue, and these compounds form a binary solid solution, showing the similarity of these two crystal structures

Synthesis and mechanistic studies of diketo acids and their bioisosteres as potential antibacterial agents

A series of diketo esters and their pertinent bioisosteres were designed and synthesized as potent antibacterial agents by targeting methionine amino peptidases (MetAPs). In the biochemical assay against purified MetAPs from Streptococcus pneumoniae (SpMetAP1a), Mycobacterium tuberculosis (MtMetAP1c), Enterococcus faecalis (EfMetAP1a) and human (HsMetAP1b), compounds 3a, 4a and 5a showed more than 85% inhibition of all the tested MetAPs at 100 μM concentration. Compounds 4a and 5a also exhibited antibacterial potential with MIC values 62.5 μg/mL (S. pneumoniae), 31.25 μg/mL (E. faecalis), 62.5 μg/mL (Escherichia coli) and 62.5 μg/mL (S. pneumoniae), 62.5 μg/mL (E. coli), respectively. Moreover, 5a also significantly inhibited the growth of multidrug resistant E. coli strains at 512 μg/mL conc., while showing no cytotoxic effect towards healthy CHO cells and thus being selected. Growth kinetics study showed significant inhibition of bacterial growth when treated with different conc. of 5a. TEM analysis also displayed vital damage to bacterial cells by 5a at MIC conc. Moreover, significant inhibition of biofilm formation was observed in bacterial cells treated with MIC conc. of 5a as visualized by SEM micrographs. Interestingly, 5a did not cause an alteration in the hemocyte density in Galleria mellonella larvae which is considered in vivo model for antimicrobial studies and was non-toxic up to a conc. of 2.5 mg/mL

Crystallization of pseudopolymorphs of some gamboge pigments. Pyridine, dimethylformamide and dimethylsulfoxide solvates of morellic acid, gambogic acid and guttiferic acid

Morellic acid, gambogic acid and guttiferic acid are related naturally-occurring xanthone pigments that yield X-ray quality crystals only from solvents like pyridine, dimethylformamide (dmf) and dimethyl sulfoxide (dmso). The structures of four of these crystals have been determined and are found to contain solvents of crystallization. The solvents hydrogen bond to the carboxyl groups with O-H…O/N motifs previously seen in other carboxylic acids. Distinctive, however, is the presence of an extended though somewhat diffuse array of C-H…O hydrogen bonds that aggregates the entire solute-solvent assemblage in a multi-point manner. Pyridine and dmf are able to mimic each other with respect to their hydrogen bond donating and accepting characteristics and in this respect play equivalent roles in their solvates with morellic acid and gambogic acid. Dmso is seen to self-associate in its guttiferic acid solvate. It is possible that these solvents with multiple hydrogen bonding donor and acceptor capability can act as hydrogen bond nucleators, providing just enough rigidity to the solutes to ensure crystallization

Discovery of a new genetic variant of methionine aminopeptidase from Streptococci with possible post-translational modifications: biochemical and structural characterization.

Protein N-terminal methionine excision is an essential co-translational process that occurs in the cytoplasm of all organisms. About 60-70% of the newly synthesized proteins undergo this modification. Enzyme responsible for the removal of initiator methionine is methionine aminopeptidase (MetAP), which is a dinuclear metalloprotease. This protein is conserved through all forms of life from bacteria to human except viruses. MetAP is classified into two isoforms, Type I and II. Removal of the map gene or chemical inhibition is lethal to bacteria and to human cell lines, suggesting that MetAP could be a good drug target. In the present study we describe the discovery of a new genetic variant of the Type I MetAP that is present predominantly in the streptococci bacteria. There are two inserts (insert one: 27 amino acids and insert two: four residues) within the catalytic domain. Possible glycosylation and phosphorylation posttranslational modification sites are identified in the 'insert one'. Biochemical characterization suggests that this enzyme behaves similar to other MetAPs in terms of substrate specificity. Crystal structure Type Ia MetAP from Streptococcus pneumoniae (SpMetAP1a) revealed that it contains two molecules in the asymmetric unit and well ordered inserts with structural features that corroborate the possible posttranslational modification. Both the new inserts found in the SpMetAP1a structurally align with the P-X-X-P motif found in the M. tuberculosis and human Type I MetAPs as well as the 60 amino acid insert in the human Type II enzyme suggesting possible common function. In addition, one of the β-hairpins within in the catalytic domain undergoes a flip placing a residue which is essential for enzyme activity away from the active site and the β-hairpin loop of this secondary structure in the active site obstructing substrate binding. This is the first example of a MetAP crystallizing in the inactive form

Steroidal aromatase inhibitors : Model receptor surfaces and 3D QSAR^†

1054-1062Receptor surfaces have been generated with a training set of 50 steroids active against cytochrome P450 enzyme, aromatase, using the Drug Discovery Workbench (Cerius2). A combination of van der Waals-electrostatic and Wyvill-partial- charge force fields together with overlay of 17- and 13-atoms of the steroid ligand resulted in four different receptor surface models. These models have high conventional and cross-validated r2, q2 values (> 0.8) for 50 training set molecules with the four components, vdW-17A, vdW-13A, Wsc-17A, Wsc-13A. Binding energies of six synthetic 2-oxasteroid analogues are evaluated with receptor surfaces and their biological activity predicted through 3D QSAR. Ligand-receptor binding is examined in relation to (1) van der Waals vs. Wyvill force fields, (2) 17- vs. 13-atoms overlay, (3) conformation of the 2-oxasteroid. Our computations show that replacement of C2-methylene group with an O-atom in the A-ring of androgens (2-oxasteroids) is accommodated during recognition by the receptor

Biochemical characterization of <i>Sp</i>MetAP1a.

<p>a) Enzyme binding curve of the Met-pNA at varied concentrations is depicted with the fit value of 0.97924. b) Metal dependency on the activity of the enzyme is tested using five different metal salts ranging from 1-1000 µM. Cobalt is identified as the best co-factor followed by manganese. In the presence of nickel, negligible activity was observed. Zinc and magnesium did not activate the enzyme. c) Activity dependency of the <i>Sp</i>MetAP1a on pH change. Maximum activity was observed at pH 7.5. d) Substrate specificity of the <i>Sp</i>MetAP1a. Among the eleven amino acid-<i>p</i>NA substrates tested, only methionine was hydrolyzed.</p

Inactive conformation of the <i>Sp</i>MetAP1a.

<p>Cartoon representation of the structural alignment of <i>Sp</i>MetAP1a (yellow) and <i>Ec</i>MetAP1a (red). Note that the β-hairpin loop collapses in to the active site there by the peptide with methionine on the amino terminus cannot bind to the enzyme.</p