Discovery, Isolation, and Structure Elucidation of Dretamycin

The Candida albicans fitness test is a whole cell screening platform that utilizes a mixed-pool of C. albicans mutants, each of which carries a heterozygous deletion of a particular gene. In the presence of an antifungal inhibitor, a subset of these mutants exhibits a growth phenotype of hypersensitivity or hyposensitivity. Collectively these mutants reflect aspects of the mechanism of action of the compound in question. In the course of screening natural products a culture of Streptomyces sp. MS-1-4 was discovered to produce a compound, dretamycin, which yielded a fitness profile exhibiting significant hypersensitivity of the <i>DRE2</i> heterozygote and hyposensitivity of the <i>DIP5</i> heterozygote. Herein we report the production, isolation, and structure elucidation of dretamycin

Isolation, Structure, and Biological Activity of Phaeofungin, a Cyclic Lipodepsipeptide from a <i>Phaeosphaeria</i> sp. Using the Genome-Wide <i>Candida albicans</i> Fitness Test

Phaeofungin (<b>1</b>), a new cyclic depsipeptide isolated from <i>Phaeosphaeria</i> sp., was discovered by application of reverse genetics technology, using the <i>Candida albicans</i> fitness test (<i>Ca</i>FT). Phaeofungin is comprised of seven amino acids and a β,γ-dihydroxy-γ-methylhexadecanoic acid arranged in a 25-membered cyclic depsipeptide. Five of the amino acids were assigned with d-configurations. The structure was elucidated by 2D-NMR and HRMS-MS analysis of the natural product and its hydrolyzed linear peptide. The absolute configuration of the amino acids was determined by Marfey’s method by complete and partial hydrolysis of <b>1</b>. The <i>Ca</i>FT profile of the phaeofungin-containing extract overlapped with that of phomafungin (<b>3</b>), another structurally different cyclic lipodepsipeptide isolated from a <i>Phoma</i> sp. using the same approach. Comparative biological characterization further demonstrated that these two fungal lipodepsipeptides are functionally distinct. While phomafungin was potentiated by cyclosporin A (an inhibitor of the calcineurin pathway), phaeofungin was synergized with aureobasidin A (2) (an inhibitor of the sphingolipid biosynthesis) and to some extent caspofungin (an inhibitor of glucan synthase). Furthermore, phaeofungin caused ATP release in wild-type <i>C. albicans</i> strains but phomafungin did not. It showed modest antifungal activity against <i>C. albicans</i> (MIC 16–32 μg/mL) and better activity against <i>Aspergillus fumigatus</i> (MIC 8–16 μg/mL) and <i>Trichophyton mentagrophytes</i> (MIC 4 μg/mL). The linear peptide was inactive, suggesting that the macrocyclic depsipeptide ring is essential for target engagement and antifungal activity

Identification of Highly Specific Diversity-Oriented Synthesis-Derived Inhibitors of Clostridium difficile

In 2013, the Centers for Disease Control highlighted Clostridium difficile as an urgent threat for antibiotic-resistant infections, in part due to the emergence of highly virulent fluoroquinolone-resistant strains. Limited therapeutic options currently exist, many of which result in disease relapse. We sought to identify molecules specifically targeting <i>C. difficile</i> in high-throughput screens of our diversity-oriented synthesis compound collection. We identified two scaffolds with apparently novel mechanisms of action that selectively target <i>C. difficile</i> while having little to no activity against other intestinal anaerobes; preliminary evidence suggests that compounds from one of these scaffolds target the glutamate racemase. In vivo efficacy data suggest that both compound series may provide lead optimization candidates

Discovery of Potent EV71 Capsid Inhibitors for Treatment of HFMD

Enterovirus 71 (EV71) is a major causative agent of hand, foot, and mouth disease (HFMD), which can spread its infections to the central nervous and other systems with severe consequences. The viral caspid protein VP1 is a well-known target for antiviral efficacy because its occupancy by suitable compounds could stabilize the virus capsid, thus preventing uncoating of virus for RNA release. In this Letter, design, synthesis, and biological evaluation of novel anti-EV71 agents (aminopyridyl 1,2,5-thiadiazolidine 1,1-dioxides) are described. One of the most promising compounds (<b>14</b>) showed excellent antiviral activity against EV71 (EC₅₀ = 4 nM) and exhibited excellent <i>in vivo</i> efficacy in the EV71 infected mouse model

Synthesis and Biological Evaluation of a Series of Bile Acid Derivatives as FXR Agonists for Treatment of NASH

Farnesoid X receptor (FXR) has become a particularly attractive target for the discovery of drugs for the treatment of liver and metabolic diseases. Obeticholic acid (<b>INT-747</b>), a FXR agonist, has advanced into clinical phase III trials in patients with nonalcoholic steatohepatitis (NASH), but adverse effects (e.g., pruritus, LDL increase) were observed. Pruritus might be induced by Takeda G-protein-coupled receptor 5 (TGR5, GPBAR1), and there are chances to develop FXR agonists with higher selectivity over TGR5. In this letter, novel bile acids bearing different modifications on ring A and side chain of <b>INT-747</b> are reported and discussed. Our results indicated that the side chain of <b>INT-747</b> is amenable to a variety of chemical modifications with good FXR potency <i>in vitro</i>. Especially, compound <b>18</b> not only showed promising FXR potency and excellent pharmacokinetic properties, but also proved superior pharmacological efficacy in the HFD + CCl₄ model