Analogs of N'-hydroxy-N-(4H,5H-naphtho[1,2-d]thiazol-2-yl)methanimidamide inhibit Mycobacterium tuberculosis methionine aminopeptidases

Cobalt-Catalyzed Cross-Dehydrogenative C(sp2 )-C(sp3 ) Coupling of Oxazole/Thiazole with Ether or Cycloalkane

Direct C5-alkylation of oxazole/thiazole with ether or cycloalkane has been achieved through a cobalt-catalyzed cross-dehydrogenative coupling (CDC) process in moderate to good yields. This transformation represents the first C(sp² )-C(sp³ ) cross-coupling at the C5-position of the oxazole/thiazole via double C-H bond cleavages. Various functional groups on oxazole/thiazole substrates, as well as water and air, are well-tolerated with this concise and practical protocol, constituting straightforward access to heterocycles with great medicinal significance. A preliminary mechanism involving a radical process has also been proposed.

Biochemical and functional characterizations of tyrosine phosphatases from pathogenic and nonpathogenic mycobacteria: indication of phenyl cyclopropyl methyl-/phenyl butenyl azoles as tyrosine phosphatase inhibitors

Tyrosine phosphorylation is one of the most common means of posttranslational modifications which can generate novel recognition motifs for protein interactions and thereafter affecting cellular localization, protein stability, and enzyme activity. Mycobacterium tuberculosis (Mtb) possesses a wide range of signal transduction systems, including two protein tyrosine phosphatases (PtpA and PtpB). Since functional diversities between protein tyrosine phosphatases (PTPases) are illustrated by regulatory domains and subunits, we have characterized the nature of tyrosine phosphatases from slow-grower pathogenic species Mtb and from fast-grower nonpathogenic species Mycobacterium smegmatis (MS). The findings delineate that the enzymes present in MS have significantly lesser phosphatase activity than PTPases of Mtb as evidenced by low K cat/K m of recombinantly expressed proteins. The K cat/K m for Mtb PtpA was 500-1000-fold higher than MS PTPases. We have designed and synthesized phenyl cyclopropyl methyl-/phenyl butenyl azoles which inhibit growth of mycobacteria, in culture and in macrophages. The mechanism of efficacy of these compounds against mycobacteria was identified and suggested that the inhibition may possibly be mediated via the targeting of Mtb tyrosine phosphatase. The results further added that these compounds exclusively inhibit PtpA of Mtb.

Bridging of a substrate between cyclodextrin and an enzyme's active site pocket triggers a unique mode of inhibition

BACKGROUND

Methionyl-7-amino-4-methylcoumarin (MetAMC) serves as a substrate for the Escherichia coli methionine aminopeptidase (MetAP) catalyzed reaction, and is routinely used for screening compounds to identify potential antibiotic agents. In pursuit of screening the enzyme's inhibitors, we observed that 2-hydroxypropyl-β-cyclodextrin (HP-β-CD), utilized to solubilize hydrophobic inhibitors, inhibited the catalytic activity of the enzyme, and such inhibition was not solely due to sequestration of the substrate by HP-β-CD.

METHODS

The mechanistic path for the HP-β-CD mediated inhibition of MetAP was probed by performing a detailed account of steady-state kinetics, ligand binding, X-ray crystallographic, and molecular modeling studies.

RESULTS

X-ray crystallographic data of the β-cyclodextrin-substrate (β-CD-MetAMC) complex reveal that while the AMC moiety of the substrate is confined within the CD cavity, the methionine moiety protrudes outward. The steady-state kinetic data for inhibition of MetAP by HP-β-CD-MetAMC conform to a model mechanism in which the substrate is "bridged" between HP-β-CD and the enzyme's active-site pocket, forming HP-β-CD-MetAMC-MetAP as the catalytically inactive ternary complex. Molecular modeling shows that the scissile bond of HP-β-CD-bound MetAMC substrate does not reach within the proximity of the enzyme's catalytic metal center, and thus the substrate fails to undergo cleavage.

CONCLUSIONS

The data presented herein suggests that the bridging of the substrate between the enzyme and HP-β-CD cavities is facilitated by interaction of their surfaces, and the resulting complex inhibits the enzyme activity.

GENERAL SIGNIFICANCE

Due to its potential interaction with physiological proteins via sequestered substrates, caution must be exercised in HP-β-CD mediated delivery of drugs under pathophysiological conditions.

Tricyclic thiazoles are a new class of angiogenesis inhibitors

Tricyclic thiazoleamine derivatives that were identified as hits in a screen against human umbilical vein endothelial cell proliferation were subjected to a structure-activity relationship study. Two structurally superimposable scaffolds-4H-thiochromeno[4,3-d]thiazol-2-amine and 5,6-dihydro-4H-benzo[6,7]cyclohepta[1,2-d]thiazol-2-amine derivatives-yielded low-micromolar inhibitors, and two among them 37 and 43 also exhibited antiangiogenic activity in an endothelial tube formation assay. Thus, 37 and 43 can serve as leads to develop a novel class of antiangiogenic agents.