Advancement of GyrB Inhibitors for Treatment of Infections Caused by Mycobacterium tuberculosis and Non-tuberculous Mycobacteria.

The prospect of ever increasing antibiotic resistance eroding currently available treatment options for bacterial infections underscores the need to continue to identify new antibiotics, preferably those that act on novel targets or with novel mechanisms of action. Bacterial gyrase B subunit (GyrB), an essential component of bacterial gyrase required for successful DNA replication, represents such a target. We describe recent examples of GyrB inhibitors and point out their potential utility for treatment of mycobacterial diseases caused by Mycobacterium tuberculosis (TB) and non-tuberculous mycobacteria (NTM). Current therapeutic options for these diseases are often suboptimal due to resistance to current standard of care antibiotics. A future GyrB inhibitor-based antibiotic could offer a new and effective addition to the armamentarium for treatment of mycobacterial diseases and possibly for infections caused by other bacterial pathogens. One GyrB inhibitor, SPR720, has recently completed a first-in-human clinical trial and is in clinical development for the treatment of NTM and TB infections.

Regioselective Synthesis of a C-4'' Carbamate,C-6'' n-Pr Substituted Cyclitol Analogue of SL0101.

An asymmetric synthesis of two analogues of SL0101 (1) has been achieved. The effort is aimed at the discovery of inhibitors of the p90 ribosomal S6 kinase (RSK) with improved bioavailability. The route relies upon the use of the Taylor catalyst to regioselectively install C-3″ acetyl or carbamate functionality. This study led to the identification of a third-generation analogue of SL0101 with a C-4″ n-Pr-carbamate and a C-3″ acetate with improved RSK inhibitory activity.

Synthesis of novel 5-substituted-2-aminotetralin analogs: 5-HT1A and 5-HT7 G protein-coupled receptor affinity, 3D-QSAR and molecular modeling.

The serotonin 5-HT7 G protein-coupled receptor (GPCR) is a proposed pharmacotherapeutic target for a variety of central and peripheral indications, albeit, there are no approved drugs selective for binding 5-HT7. We previously reported that a lead analog based on the 5-substituted-N,N-disubstituted-1,2,3,4-tetrahydronaphthalen-2-amine (5-substituted-2-aminotetralin, 5-SAT) scaffold binds with high affinity at the 5-HT7 GPCR, and can treat symptoms of autism in mouse models; subsequently, the lead was found to have high affinity at the 5-HT1A GPCR. Herein, we report the synthesis of novel 5-SAT analogs to develop a 3-dimensional quantitative structure-affinity relationship (3D-QSAR) at the human 5-HT7 receptor for comparison with similar studies at the highly homologous 5-HT1A receptor. We report 35 new 5-SAT ligands, some with very high affinity (Ki ≤ 1 nM) and stereoselectivity at 5-HT7 + or 5-HT1A receptors, several with modest selectivity (up to 12-fold) for binding at 5-HT7, and, several ligands with high selectivity (up to 40-fold) at the 5-HT1A receptor. 3D-QSAR results indicate that steric extensions at the C(5)-position improve selectivity for the 5-HT7 over 5-HT1A receptor, while steric and hydrophobic extensions at the chiral C(2)-amino position impart 5-HT1A selectivity. In silico receptor homology modeling studies, supplemented with molecular dynamics simulations and binding free energy calculations, were used to rationalize experimentally-determined receptor selectivity and stereoselective affinity results. The data from these studies indicate that the 5-SAT chemotype, previously shown to be safe and efficacious in rodent paradigms of neurodevelopmental and neuropsychiatric disorders, is amenable to structural modification to optimize affinity at serotonin 5-HT7 vs. 5-HT1A GPCRs, as may be required for successful clinical translation.

A New, Short, and Stereocontrolled Synthesis of C2-Symmetric 1,2-Diamines.

The previously unknown 5-spirocyclohexylisoimidazole has been made efficiently and simply by reaction of ammonia, glyoxal hydrate, and cyclohexanone. It is a very useful precursor for the diastereocontrolled synthesis of many C2-symmetric 1,2-diamines, a class which is important for the generation of a variety of C2-symmetric reagents and catalysts for enantioselective synthesis.

An Orally Active Phenylaminotetralin-Chemotype Serotonin 5-HT7 and 5-HT1A Receptor Partial Agonist that Corrects Motor Stereotypy in Mouse Models.

Stereotypy (e.g., repetitive hand waving) is a key phenotype of autism spectrum disorder, Fragile X and Rett syndromes, and other neuropsychiatric disorders, and its severity correlates with cognitive and attention deficits. There are no effective treatments, however, for stereotypy. Perturbation of serotonin (5-HT) neurotransmission contributes to stereotypy, suggesting that distinct 5-HT receptors may be pharmacotherapeutic targets to treat stereotypy and related neuropsychiatric symptoms. For example, preclinical studies indicate that 5-HT7 receptor activation corrects deficits in mouse models of Fragile X and Rett syndromes, and clinical trials for autism are underway with buspirone, a 5-HT1A partial agonist with relevant affinity at 5-HT7 receptors. Herein, we report the synthesis, in vitro molecular pharmacology, behavioral pharmacology, and pharmacokinetic parameters in mice after subcutaneous and oral administration of (+)-5-(2'-fluorophenyl)-N,N-dimethyl-1,2,3,4-tetrahydronaphthalen-2-amine ((+)-5-FPT), a new, dual partial agonist targeting both 5-HT7 (Ki = 5.8 nM, EC50 = 34 nM) and 5-HT1A (Ki = 22 nM, EC50 = 40 nM) receptors. Three unique, heterogeneous mouse models were used to assess the efficacy of (+)-5-FPT to reduce stereotypy: idiopathic jumping in C58/J mice, repetitive body rotations in C57BL/6J mice treated with the NMDA antagonist, MK-801, and repetitive head twitching in C57BL/6J mice treated with the 5-HT2 agonist, DOI. Systemic (+)-5-FPT potently and efficaciously reduced or eliminated stereotypy in each of the mouse models without altering locomotor behavior on its own, and additional tests showed that (+)-5-FPT, at the highest behaviorally active dose tested, enhanced social interaction and did not cause behaviors indicative of serotonin syndrome. These data suggest that (+)-5-FPT is a promising medication for treating stereotypy in psychiatric disorders.

Reversal of the importance of steric and electronic effects in the base-promoted α-silylation of sulfides.

Lithiation of α-C-H groups in organic substrates by RLi or R2NLi followed by silylation with R'3SiCl generally provides analogous products regardless of the R' group of R'3SiCl. A striking exception using 3,4-benzothiophane as substrate depending on whether R' is methyl, phenyl, or isopropyl is demonstrated. With R' = Me or Ph, the geminal α,α-bis-silylated products result whereas with i-Pr3SiCl the trans-α,α'-bis-silylated sulfide is formed. The latter pathway provides ready access to the C2-symmetric enantiomers of trans-2,5-bis(triisopropylsilyl)-3,4-benzothiophane.

De novo synthesis and biological evaluation of C6″-substituted C4″-amide analogues of SL0101.

In an effort to improve upon the in vivo half-life of the known ribosomal s6 kinase (RSK) inhibitor SL0101, C4″-amide/C6″-alkyl substituted analogues of SL0101 were synthesized and evaluated in cell-based assays. The analogues were prepared using a de novo asymmetric synthetic approach, which featured Pd-π-allylic catalyzed glycosylation for the introduction of a C4″-azido group. Surprisingly replacement of the C4″-acetate with a C4″-amide resulted in analogues that were no longer specific for RSK in cell-based assays.

Improving the affinity of SL0101 for RSK using structure-based design.

Enhanced activity of the Ser/Thr protein kinase, RSK, is associated with transformation and metastasis, which suggests that RSK is an attractive drug target. The natural product, SL0101 (kaempferol 3-O-(3″,4″-di-O-acetyl-α-L-rhamnopyranoside), has been shown to be a RSK selective inhibitor. However, the Ki for SL0101 is 1 µM with a half-life of less than 30 min in vivo. To identify analogues with improved efficacy we designed a set of analogues based on the crystallographic model of SL0101 in complex with the RSK2 N-terminal kinase domain. We identified an analogue with a 5″-n-propyl group on the rhamnose that has > 40-fold improved affinity for RSK relative to SL0101 in an in vitro kinase assay. This analogue preferentially inhibited the proliferation of the human breast cancer line, MCF-7, versus the normal untransformed breast line, MCF-10A, which is consistent with results using SL0101. However, the efficacy of the 5″-n-propyl analogue to inhibit MCF-7 proliferation was only two-fold better than for SL0101, which we hypothesize is due to limited membrane permeability. The improved affinity of the 5″-n-propyl analogue for RSK will aid in the design of future compounds for in vivo use.