Application of Virtual Screening to the Identification of New LpxC Inhibitor Chemotypes, Oxazolidinone and Isoxazoline

This report summarizes the identification and synthesis of novel LpxC inhibitors aided by computational methods that leveraged numerous crystal structures. This effort led to the identification of oxazolidinone and isoxazoline inhibitors with potent in vitro activity against P. aeruginosa and other Gram-negative bacteria. Representative compound 13f demonstrated efficacy against P. aeruginosa in a mouse neutropenic thigh infection model. The antibacterial activity against K. pneumoniae could be potentiated by Gram-positive antibiotics rifampicin (RIF) and vancomycin (VAN) in both in vitro and in vivo models.

Potent nonimmunosuppressive cyclophilin inhibitors with improved pharmaceutical properties and decreased transporter inhibition

Nonimmunosuppressive cyclophilin inhibitors have demonstrated efficacy for the treatment of hepatitis C infection (HCV). However, alisporivir, cyclosporin A, and most other cyclosporins are potent inhibitors of OATP1B1, MRP2, MDR1, and other important drug transporters. Reduction of the side chain hydrophobicity of the P4 residue preserves cyclophilin binding and antiviral potency while decreasing transporter inhibition. Representative inhibitor 33 (NIM258) is a less potent transporter inhibitor relative to previously described cyclosporins, retains anti-HCV activity in cell culture, and has an acceptable pharmacokinetic profile in rats and dogs. An X-ray structure of 33 bound to rat cyclophilin D is reported.

Chemoselective and enantioselective oxidation of indoles employing aspartyl peptide catalysts

Catalytic enantioselective indole oxidation is a process of particular relevance to the chemistry of complex alkaloids, as it has been implicated in their biosynthesis. In the context of synthetic methodology, catalytic enantioselective indole oxidation allows a rapid and biomimetic entry into several classes of alkaloid natural products. Despite this potentially high utility in the total synthesis, reports of catalytic enantioselective indole oxidation remain sparse. Here we report a highly chemoselective catalytic system for the indole oxidation that delivers 3-hydroxy-indolenines with good chemical yields and moderate to high levels of enantio- and diastereoselectivity (up to 95:5 er and up to 92:8 dr). These results represent, to our knowledge, the most selective values yet reported in the literature for catalytic asymmetric indole oxidation. Furthermore, the utility of enantioenriched hydroxy-indolenines in stereospecific rearrangements is demonstrated.

Total synthesis of (-)-himandrine

We describe the first total synthesis of (-)-himandrine, a member of the class II galbulimima alkaloids. Noteworthy features of this chemistry include a diastereoselective Diels-Alder reaction in the rapid synthesis of the tricycle ABC-ring system in an enantiomerically enriched form, the use of a formal [3+3] annulation strategy to secure the CDE-ring system with complete diastereoselection, and successful implementation of our biogenetically inspired oxidative spirocyclization of an advanced intermediate. The successful and direct late-stage formation of the F-ring in the hexacyclic core of himandrine drew on the power of biogenetic considerations and fully utilized the inherent chemistry of a plausible biosynthetic intermediate.

Total synthesis and absolute stereochemical assignment of (+)- and (-)-galbulimima alkaloid 13

We describe the total synthesis of (+)- and (-)-galbulimima alkaloid 13. The absolute stereochemistry of natural (-)-galbulimima alkaloid 13 is revised to 2S. Sequential use of catalytic cross-coupling and cross-metathesis reactions followed by an intramolecular Diels-Alder reaction provided the required trans-decalin AB-ring system and masked the C16 carbonyl as an N-vinyl carbamate for late-stage unveiling in the form of the necessary C16 enone. A vinyl radical cyclization secured the C-ring, while successful execution of our strategy for introduction of the CDE-ring system in complex galbulimima alkaloids provided the target pentacycle with complete diastereoselection.

Cleavable Hydrophilic Linker for One-Bead-One-Compound Sequencing of Oligomer Libraries by Tandem Mass Spectrometry

We have developed a method for the rapid and unambiguous identification of sequences of hit compounds from one-bead-one-compound combinatorial libraries of peptide and peptoid ligands. The approach uses a cleavable linker that is hydrophilic to help reduce nonspecific binding to biological samples and allows for the attachment of a halogen tag, which greatly facilitates post-screening sequencing by tandem mass spectrometry (MS/MS). The linker is based on a tartaric acid unit, which, upon cleavage from resin, generates a C-terminal aldehyde. This aldehyde can then be derivatized with a bromine-containing amino-oxy compound that serves as an isotope tag for subsequent MS/MS analysis of y-ion fragments. We have applied this linker and method to the syntheses of a number of peptoids that vary in sequence and length and have also demonstrated single-bead sequencing of a peptoid pentamer. The linker is also shown to have very low levels of nonspecific binding to proteins.