Synthesis, SAR study, and biological evaluation of novel 2,3-dihydro-1H-imidazo[1,2-a]benzimidazole derivatives as phosphodiesterase 10A inhibitors.

Phosphodiesterase 10A (PDE10A) inhibitors were designed and synthesized based on the dihydro-imidazobenzimidazole scaffold. Compound 5a showed moderate inhibitory activity and good permeability, but unfavorable high P-glycoprotein (P-gp) liability for brain penetration. We performed an optimization study to improve both the P-gp efflux ratio and PDE10A inhibitory activity. As a result, 6d was identified with improved P-gp liability and high PDE10A inhibitory activity. Compound 6d also showed satisfactory brain penetration, suppressed phencyclidine-induced hyperlocomotion and improved MK-801-induced working memory deficit.

Fragment-Based Discovery of Pyrimido[1,2-b]indazole PDE10A Inhibitors.

In this study, we report the identification of potent pyrimidoindazoles as phosphodiesterase10A (PDE10A) inhibitors by using the method of fragment-based drug discovery (FBDD). The pyrazolopyridine derivative 2 was found to be a fragment hit compound which could occupy a part of the binding site of PDE10A enzyme by using the method of the X-ray co-crystal structure analysis. On the basis of the crystal structure of compound 2 and PDE10A protein, a number of compounds were synthesized and evaluated, by means of structure-activity relationship (SAR) studies, which culminated in the discovery of a novel pyrimidoindazole derivative 13 having good physicochemical properties.

Novel benzimidazole derivatives as phosphodiesterase 10A (PDE10A) inhibitors with improved metabolic stability.

In this study, we report the identification of potent benzimidazoles as PDE10A inhibitors. We first identified imidazopyridine 1 as a high-throughput screening hit compound from an in-house library. Next, optimization of the imidazopyridine moiety to improve inhibitory activity gave imidazopyridinone 10b. Following further structure-activity relationship development by reducing lipophilicity and introducing substituents, we acquired 35, which exhibited both improved metabolic stability and reduced CYP3A4 time-dependent inhibition.

Synthesis and antifungal activity of ASP9726, a novel echinocandin with potent Aspergillus hyphal growth inhibition.

The synthesis and antifungal activity of ASP9726, a novel echinocandin with potent Aspergillus hyphal growth inhibition and significantly improved MIC against Candida parapsilosis and echinocandin resistant-Candida is described.

Total synthesis of chloropeptin II (complestatin) and chloropeptin I.

The first total synthesis of chloropeptin II (1, complestatin) is disclosed. Key elements of the approach include the use of an intramolecular Larock indole synthesis for the initial macrocyclization, adopting conditions that permit utilization of a 2-bromoaniline, incorporating a terminal alkyne substituent (-SiEt(3)) that sterically dictates the indole cyclization regioselectivity, and benefiting from an aniline protecting group (-Ac) that enhances the atropdiastereoselectivity and diminishes the strained indole reactivity toward subsequent electrophilic reagents. Not only did this key reaction provide the fully functionalized right-hand ring system of 1 in superb conversion (89%) and good atropdiastereoselectivity (4:1 R:S), but it also represents the first reported example of what will prove to be a useful Larock macrocyclization strategy. Subsequent introduction of the left-hand ring system enlisting an aromatic nucleophilic substitution reaction for macrocyclization with biaryl ether formation completed the assemblage of the core bicyclic structure of 1. Intrinsic in the design of the approach and by virtue of the single-step acid-catalyzed conversion of chloropeptin II (1) to chloropeptin I (2), the route also provides a total synthesis of 2.

FR290581, a novel sordarin derivative: synthesis and antifungal activity.

Sordarin is a unique natural product antifungal agent that is an inhibitor of elongation factor 2. To improve biological activity, we synthesized various compounds by novel modification of the aglycone, sordaricin. As a result, we have discovered the novel sordarin derivative FR290581. This compound exhibited superior activity and a good pharmacokinetic profile, and also displayed good in vivo activity against Candida albicans.

Use of a serum-based antifungal susceptibility assay to predict the in vivo efficacy of novel echinocandin compounds.

In vitro susceptibility assays of antifungal activity do not always accurately predict in vivo efficacy. As well as having a clear clinical importance, the ability to predict efficacy is also essential for effective screening of novel drug compounds. Initial screening of novel compounds must often be based on in vitro data. The present report describes the use of serum-MIC, an in vitro test of antifungal susceptibility, to accurately predict in vivo efficacy of echinocandin drugs in a mouse model of disseminated candidiasis. The basis of the serum-MIC method was to measure the inhibitory activity of a test compound against Candida albicans hyphal growth in the presence of pooled mouse serum. For 13 previously uncharacterized echinocandin compounds, as well as for the known echinocandin drugs, micafungin and caspofungin, serum-MIC determinations were shown to give better correlation to efficacy in the animal model than conventional, CLSI standard, in vitro antifungal susceptibility tests. The most accurate prediction of efficacy was obtained when the serum-MIC was adjusted in relation to the serum concentration at 30 min post-treatment. Furthermore, when the efficacy of micafungin was determined by measuring C. albicans kidney burden in the mouse model of infection, the adjusted serum-MIC consistently reflected the effective serum concentrations. Our data indicate that determination of serum-MIC values will facilitate prediction of the in vivo potency of new antifungal compounds such as novel echinocandins.

Novel echinocandin antifungals. Part 2: Optimization of the side chain of the natural product FR901379. Discovery of micafungin.

Further optimization of the potent antifungal activity of side chain analogs of the natural product FR901379 led to the discovery of compound 8 with an excellent, well-balanced profile. Potent compounds with reduced hemolytic potential were designed based upon a disruption of the linearity of the terphenyl lipophilic side chain. The optimized compound (8, FK463, micafungin) displayed the best balance and was selected as the clinical candidate.

Novel echinocandin antifungals. Part 1: novel side-chain analogs of the natural product FR901379.

A series of novel acylated analogs of the novel water-soluble echinocandin FR901379 have been prepared and evaluated for antifungal and hemolytic activity. A relationship between antifungal activity and lipophilicity of the acyl side chain, expressed as ClogP was demonstrated, and an analog (3c) with 5.5- to 8-fold superior in vivo activity relative to the previously disclosed 4-(n-octyloxy)benzoyl side chain analog, FR131535 obtained.

Determination of antifungal activities in serum samples from mice treated with different antifungal drugs allows detection of an active metabolite of itraconazole.

To establish an in vitro method of predicting in vivo efficacy of antifungal drugs against Candida albicans and Aspergillus fumigatus, the antifungal activities of fluconazole, itraconazole, and amphotericin B were determined in mouse serum. The minimum inhibitory concentration (MIC) of each drug was measured using mouse serum as a diluent. For C. albicans, the assay endpoint of azoles was defined as inhibition of mycelial extension (mMIC) and for A. fumigatus, as no growth (MIC). The MICs of amphotericin B for both pathogens were defined as the MIC at which no mycelial growth occurred. Serum MIC or mMIC determinations were then used to estimate the concentration of the drugs in serum of mice treated with antifungal drugs by multiplying the antifungal titer of the serum samples by the serum (m)MIC. The serum drug concentrations were also determined by HPLC. The serum concentrations estimated microbiologically showed good agreement with those determined by HPLC, except for itraconazole. Analysis of the serum samples from itraconazole-treated mice by a sensitive bioautography revealed the presence of additional spots, not seen in control samples of itraconazole. The bioautography assay demonstrated that the additional material detected in serum from mice treated with itraconazole was an active metabolite of itraconazole. The data showed that the apparent reduction in the itraconazole serum concentration as determined by HPLC was the result of the formation of an active metabolite, and that the use of a microbiological method to measure serum concentrations of drugs can provide a method for prediction of in vivo efficacy of antifungal drugs.