Maiko Iida

Crystal structure of enoyl-acyl carrier protein reductase (FabK) from Streptococcus pneumoniae reveals the binding mode of an inhibitor.

Enoyl–acyl carrier protein (ACP) reductases are critical for bacterial type II fatty acid biosynthesis and thus are attractive targets for developing novel antibiotics. We determined the crystal structure of enoyl–ACP reductase (FabK) from Streptococcus pneumoniae at 1.7 Å resolution. There was one dimer per asymmetric unit. Each subunit formed a triose phosphate isomerase (TIM) barrel structure, and flavin mononucleotide (FMN) was bound as a cofactor in the active site. The overall structure was similar to the enoyl–ACP reductase (ER) of fungal fatty acid synthase and to 2‐nitropropane dioxygenase (2‐ND) from Pseudomonas aeruginosa, although there were some differences among these structures. We determined the crystal structure of FabK in complex with a phenylimidazole derivative inhibitor to envision the binding site interactions. The crystal structure reveals that the inhibitor binds to a hydrophobic pocket in the active site of FabK, and this is accompanied by induced‐fit movements of two loop regions. The thiazole ring and part of the ureido moiety of the inhibitor are involved in a face‐to‐face π–π stacking interaction with the isoalloxazine ring of FMN. The side‐chain conformation of the proposed catalytic residue, His144, changes upon complex formation. Lineweaver–Burk plots indicate that the inhibitor binds competitively with respect to NADH, and uncompetitively with respect to crotonoyl coenzyme A. We propose that the primary basis of the inhibitory activity is competition with NADH for binding to FabK, which is the first step of the two‐step ping‐pong catalytic mechanism.

Functional Analysis of Synthetic Substructures of Polytheonamide B: A Transmembrane Channel-Forming Peptide†

1 couldserve as a minimum-structure platform for investigatingrequirements for ion-channel functions and designing noveltransmembrane channels. The structure–function relation-ships of various analogues of 1 should shed light on thespecificconstituentaminoacidsandsequencesthatencodeitsunique channel function.

Characterization of Antifungal Activity and Nail Penetration of ME1111, a New Antifungal Agent for Topical Treatment of Onychomycosis

ABSTRACT Fungal nail infection (onychomycosis) is a prevalent disease in many areas of the world, with a high incidence approaching 23%. Available antifungals to treat the disease suffer from a number of disadvantages, necessitating the discovery of new efficacious and safe antifungals. Here, we evaluate the in vitro antifungal activity and nail penetration ability of ME1111, a novel antifungal agent, along with comparator drugs, including ciclopirox, amorolfine, terbinafine, and itraconazole. ME1111 showed potent antifungal activity against Trichophyton rubrum and Trichophyton mentagrophytes (the major etiologic agents of onychomycosis) strains isolated in Japan and reference fungal strains with an MIC range of 0.12 to 0.5 mg/liter and an MIC50 and MIC90 of 0.5 mg/liter for both. Importantly, none of the tested isolates showed an elevated ME1111 MIC. Moreover, the antifungal activity of ME1111 was minimally affected by 5% wool keratin powder in comparison to the other antifungals tested. The ME1111 solution was able to penetrate human nails and inhibit fungal growth in a dose-dependent manner according to the TurChub assay. In contrast, 8% ciclopirox and 5% amorolfine nail lacquers showed no activity under the same conditions. ME1111 demonstrated approximately 60-fold-greater selectivity in inhibition of Trichophyton spp. than of human cell lines. Our findings demonstrate that ME1111 possesses potent antidermatophyte activity, maintains this activity in the presence of keratin, and possesses excellent human nail permeability. These results suggest that ME1111 is a promising topical medication for the treatment of onychomycosis and therefore warrants further clinical evaluation.

Design and synthesis of potent substrate-based inhibitors of the Trypanosoma cruzi dihydroorotate dehydrogenase

Chagas disease, caused by the parasitic protozoan Trypanosoma cruzi, is the leading cause of heart disease in Latin America. T. cruzi dihydroorotate dehydrogenase (DHODH), which catalyzes the production of orotate, was demonstrated to be essential for T. cruzi survival, and thus has been considered as a potential drug target to combat Chagas disease. Here we report the design and synthesis of 75 compounds based on the orotate structure. A comprehensive structure-activity relationship (SAR) study revealed two 5-substituted orotate analogues (5u and 5v) that exhibit Kiapp values of several ten nanomolar level and a selectivity of more than 30,000-fold over human DHODH. The information presented here will be invaluable in the search for next-generation drug leads for Chagas disease.

Erratum: Total synthesis of the large non-ribosomal peptide polytheonamide B

Nature Chemistry doi: 10.1038/nchem.554 (2010); published online: 21 February 2010; corrected online 23 February 2010. In the version of this Article originally published online, an in-house error led to the incorrect representation of stereochemistry in Figs 1, 2 and 6. These have now been corrected in all versions of the Article.