Amino-Heterocycle Tetrahydroisoquinoline CXCR4 Antagonists with Improved ADME Profiles via Late-Stage Buchwald Couplings.

This work surveys a variety of diamino-heterocycles as an isosteric replacement for the piperazine substructure of our previously disclosed piperarinyl-tetrahydroisoquinoline containing CXCR4 antagonists. A late-stage Buchwald coupling route was developed for rapid access to final compounds from commercial building blocks. Among 13 analogs in this study, compound 31 embodying an aza-piperazine linkage was found to have the best overall profile with potent CXCR4 inhibitory activity and favorable in vitro absorption, distribution, metabolism, and excretion (ADME) properties. An analysis of the calculated physiochemical parameters (ROF, cLogD) and the experimental ADME attributes of the analogs lead to the selection of 31 for pharmacokinetic studies in mice. Compared with the clinical compound AMD11070, compound 31 has no CYP450 3A4 or 2D6 inhibition, higher metabolic stability and PAMPA permeability, greatly improved physiochemical parameters, and superior oral bioavailability (%F = 24). A binding rationale for 31 within CXCR4 was elucidated from docking and molecular simulation studies.

Design, Synthesis, and Pharmacological Evaluation of Second-Generation Tetrahydroisoquinoline-Based CXCR4 Antagonists with Favorable ADME Properties.

CXCR4 is a G-protein-coupled receptor that interacts with its cognate ligand, CXCL12, to synchronize many physiological responses and pathological processes. Disruption of the CXCL12-CXCR4 circuitry by small-molecule antagonists has emerged as a promising strategy for cancer intervention. We previously disclosed a hit-to-lead effort that led to the discovery of a series of tetrahydroisoquinoline-based CXCR4 antagonists exemplified by the lead compound TIQ15. Herein, we describe our medicinal-chemistry efforts toward the redesign of TIQ15 as a result of high mouse-microsomal clearance, potent CYP2D6 inhibition, and poor membrane permeability. Guided by the in vitro ADME data of TIQ15, structural modifications were executed to provide compound 12a, which demonstrated a reduced potential for first-pass metabolism while maintaining CXCR4 potency. Subsequent SAR studies and multiparameter optimization of 12a resulted in the identification of compound 25o, a highly potent, selective, and metabolically stable CXCR4 antagonist possessing good intestinal permeability and low risk of CYP-mediated drug-drug interactions.

Discovery of N-Alkyl Piperazine Side Chain Based CXCR4 Antagonists with Improved Drug-like Properties.

A novel series of CXCR4 antagonists with piperidinyl and piperazinyl alkylamine side chains designed as butyl amine replacements are described. Several of these compounds showed similar activity to the parent compound TIQ-15 (5) in a SDF-1 induced calcium flux assay. Preliminary structure-activity relationship investigations led us to identify a series containing N-propyl piperazine side chain analogs exemplified by 16 with improved off-target effects as measured in a muscarinic acetylcholine receptor (mAChR) calcium flux assay and in a limited drug safety panel screen. Further efforts to explore SAR and optimize drug properties led to the identification of the N'-ethyl-N-propyl-piperazine tetrahydroisoquinoline derivative 44 and the N-propyl-piperazine benzimidazole compound 37, which gave the best overall profiles with no mAChR or CYP450 inhibition, good permeability in PAMPA assays, and metabolic stability in human liver microsomes.

Synthesis of Novel Tetrahydroisoquinoline CXCR4 Antagonists with Rigidified Side-Chains.

A structure-activity relationship study of potent TIQ15-derived CXCR4 antagonists is reported. In this investigation, the TIQ15 side-chain was constrained to improve its drug properties. The cyclohexylamino congener 15a was found to be a potent CXCR4 inhibitor (IC50 = 33 nM in CXCL12-mediated Ca2+ flux) with enhanced stability in liver microsomes and reduced inhibition of CYP450 (2D6). The improved CXCR4 antagonist 15a has potential therapeutic application as a single agent or combinatory anticancer therapy.

Discovery of Tetrahydroisoquinoline-Containing CXCR4 Antagonists with Improved in Vitro ADMET Properties.

CXCR4 is a seven-transmembrane receptor expressed by hematopoietic stem cells and progeny, as well as by ≥48 different cancers types. CXCL12, the only chemokine ligand of CXCR4, is secreted within the tumor microenvironment, providing sanctuary for CXCR4+ tumor cells from immune surveillance and chemotherapeutic elimination by (1) stimulating prosurvival signaling and (2) recruiting CXCR4+ immunosuppressive leukocytes. Additionally, distant CXCL12-rich niches attract and support CXCR4+ metastatic growths. Accordingly, CXCR4 antagonists can potentially obstruct CXCR4-mediated prosurvival signaling, recondition the CXCR4+ leukocyte infiltrate from immunosuppressive to immunoreactive, and inhibit CXCR4+ cancer cell metastasis. Current small molecule CXCR4 antagonists suffer from poor oral bioavailability and off-target liabilities. Herein, we report a series of novel tetrahydroisoquinoline-containing CXCR4 antagonists designed to improve intestinal absorption and off-target profiles. Structure-activity relationships regarding CXCR4 potency, intestinal permeability, metabolic stability, and cytochrome P450 inhibition are presented.

Synthesis and SAR of 1,2,3,4-Tetrahydroisoquinoline-Based CXCR4 Antagonists.

CXCR4 is the most common chemokine receptor expressed on the surface of many cancer cell types. In comparison to normal cells, cancer cells overexpress CXCR4, which correlates with cancer cell metastasis, angiogenesis, and tumor growth. CXCR4 antagonists can potentially diminish the viability of cancer cells by interfering with CXCL12-mediated pro-survival signaling and by inhibiting chemotaxis. Herein, we describe a series of CXCR4 antagonists that are derived from (S)-5,6,7,8-tetrahydroquinolin-8-amine that has prevailed in the literature. This series removes the rigidity and chirality of the tetrahydroquinoline providing 2-(aminomethyl)pyridine analogs, which are more readily accessible and exhibit improved liver microsomal stability. The medicinal chemistry strategy and biological properties are described.

CCR5 receptor antagonists in preclinical to phase II clinical development for treatment of HIV.

INTRODUCTION: The chemokine receptor CCR5 has garnered significant attention in recent years as a target to treat HIV infection largely due to the approval and success of the drug Maraviroc. The side effects and inefficiencies with other first generation agents led to failed clinical trials, prompting the development of newer CCR5 antagonists. Areas covered: This review aims to survey the current status of 'next generation' CCR5 antagonists in the preclinical pipeline with an emphasis on emerging agents for the treatment of HIV infection. These efforts have culminated in the identification of advanced second-generation agents to reach the clinic and the dual CCR5/CCR2 antagonist Cenicriviroc as the most advanced currently in phase II clinical studies. Expert opinion: The clinical success of CCR5 inhibitors for treatment of HIV infection has rested largely on studies of Maraviroc and a second-generation dual CCR5/CCR2 antagonist Cenicriviroc. Although research efforts identified several promising preclinical candidates, these were dropped during early clinical studies. Despite patient access to Maraviroc, there is insufficient enthusiasm surrounding its use as front-line therapy for treatment of HIV. The non-HIV infection related development activities for Maraviroc and Cenicriviroc may help drive future interests.

The Synthesis and Antimicrobial Activity of Heterocyclic Derivatives of Totarol.

The synthesis and antimicrobial activity heterocyclic analogs of the diterpenoid totarol are described. An advanced synthetic intermediate with a ketone on the A-ring is used to attach fused heterocycles and a carbon-to-nitrogen atom replacement is made on the B-ring by de novo synthesis. A-ring analogs with an indole attached exhibit, for the first time, enhanced antimicrobial activity relative to the parent natural product. Preliminary experiments demonstrate that the indole analogs do not target the bacterial cell division protein FtsZ as had been hypothesized for totarol.

Comparison of small molecule inhibitors of the bacterial cell division protein FtsZ and identification of a reliable cross-species inhibitor.

FtsZ is a guanosine triphosphatase (GTPase) that mediates cytokinesis in bacteria. FtsZ is homologous in structure to eukaryotic tubulin and polymerizes in a similar head-to-tail fashion. The study of tubulin's function in eukaryotic cells has benefited greatly from specific and potent small molecule inhibitors, including colchicine and taxol. Although many small molecule inhibitors of FtsZ have been reported, none has emerged as a generally useful probe for modulating bacterial cell division. With the goal of establishing a useful and reliable small molecule inhibitor of FtsZ, a broad biochemical cross-comparison of reported FtsZ inhibitors was undertaken. Several of these molecules, including phenolic natural products, are unselective inhibitors that seem to derive their activity from the formation of microscopic colloids or aggregates. Other compounds, including the natural product viriditoxin and the drug development candidate PC190723, exhibit no inhibition of GTPase activity using protocols in this work or under published conditions. Of the compounds studied, only zantrin Z3 exhibits good levels of inhibition, maintains activity under conditions that disrupt small molecule aggregates, and provides a platform for exploration of structure-activity relationships (SAR). Preliminary SAR studies have identified slight modifications to the two side chains of this structure that modulate the inhibitory activity of zantrin Z3. Collectively, these studies will help focus future investigations toward the establishment of probes for FtsZ that fill the roles of colchicine and taxol in studies of tubulin.

Synthesis of 6,6'-binaphthopyran-2-one natural products: pigmentosin A, talaroderxines A and B.

Efficient and stereoselective syntheses of pigmentosin A, talaroderxine A, and its diastereomer talaroderxine B are reported. The binaphthyl ring system is assembled by vanadium-catalyzed phenolic coupling of tricyclic precursors. These key intermediates were prepared by Michael-Dieckmann annulation of a protected orsellinate ester, with the requisite pyranones accessed by a new variant of Ghosez's sulfone-epoxide annulation. Preliminary biological experiments are reported for pigmentosin.

Synthesis of antimicrobial natural products targeting FtsZ: (+)-totarol and related totarane diterpenes.

An efficient, convergent synthesis of totarol by a diastereoselective epoxide/alkene/arene bicyclization is described. The reported synthesis enables the preparation of related diterpenes totaradiol and totarolone as well as previously unavailable derivatives that exhibit comparable inhibition of the bacterial cell division protein FtsZ.