R. Nathan Daniels

Discovery of potent myeloid cell leukemia 1 (Mcl-1) inhibitors using fragment-based methods and structure-based design.

Myeloid cell leukemia 1 (Mcl-1), a member of the Bcl-2 family of proteins, is overexpressed and amplified in various cancers and promotes the aberrant survival of tumor cells that otherwise would undergo apoptosis. Here we describe the discovery of potent and selective Mcl-1 inhibitors using fragment-based methods and structure-based design. NMR-based screening of a large fragment library identified two chemically distinct hit series that bind to different sites on Mcl-1. Members of the two fragment classes were merged together to produce lead compounds that bind to Mcl-1 with a dissociation constant of <100 nM with selectivity for Mcl-1 over Bcl-xL and Bcl-2. Structures of merged compounds when complexed to Mcl-1 were obtained by X-ray crystallography and provide detailed information about the molecular recognition of small-molecule ligands binding Mcl-1. The compounds represent starting points for the discovery of clinically useful Mcl-1 inhibitors for the treatment of a wide variety of cancers.

Application of combinatorial chemistry science on modern drug discovery.

The science that established combinatorial chemistry as important new discipline in the 1980s and 1990s has re-emerged and infiltrated every sub-discipline within modern drug discovery and has profound impact. The application of combinatorial chemistry science has revolutioned high-throughput screening paradigms, chemical lead optimization, library purification, and post-purification sample handling, as well as in vitro and in vivo drug metabolism and pharmacokinetic assays. Although no longer in the spotlight and heralded as the savior of the drug industry, “combinatorial chemistry” is alive and well; in fact, combinatorial chemistry science is more prevalent and wide-spread than ever before.

Synthesis and SAR of analogues of the M1 allosteric agonist TBPB. Part I. Exploration of alternative benzyl and privileged structure moieties

This Letter describes the first account of the synthesis and SAR, developed through an iterative analogue library approach, of analogues of the highly selective M1 allosteric agonist TBPB. With slight structural changes, mAChR selectivity was maintained, but the degree of partial M1 agonism varied considerably.

Progress toward the Total Synthesis of Lucentamycin A: Total Synthesis and Biological Evaluation of 8-epi-Lucentamycin A

Synthetic efforts toward the cytotoxic peptides lucentamycins A-D are described that resulted in the total synthesis and biological evaluation of 8-epi-lucentamycin A in 15 steps with 2.2% overall yield. The key epi-nonproteogenic 3-methyl-4-ethylideneproline was synthesized via a titanium-mediated cycloisomerization reaction.

Synthesis and SAR of analogs of the M1 allosteric agonist TBPB. Part II: Amides, sulfonamides and ureas--the effect of capping the distal basic piperidine nitrogen.

This letter describes the further synthesis and SAR, developed through an iterative analog library approach, of analogs of the highly selective M1 allosteric agonist TBPB by deletion of the distal basic piperidine nitrogen by the formation of amides, sulfonamides and ureas. Despite the large change in basicity and topology, M1 selectivity was maintained.

A New Catalytic Cu(II)/Sparteine Oxidant System for β,β-Phenolic Couplings of Styrenyl Phenols: Synthesis of Carpanone and Unnatural Analogs

A new catalytic Cu(II)/sparteine system has been developed to promote beta,beta-phenolic couplings of styrenyl phenols en route to carpanone and related unnatural congeners in yields exceeding 85%.

Total synthesis of Ciliatamides A-C: stereochemical revision and the natural product-guided synthesis of unnatural analogs.

The first total synthesis of Ciliatamides A-C was completed, leading to a revision of the reported stereochemistry from (S,S) to the (R,R) enantiomers. Due to the expedited route, a library of over 50 unnatural ciliatamide analogs was also prepared.

Synthesis and SAR of N-(4-(4-alklylpiperazin-1-yl)phenyl)benzamides as muscarinic acetylcholine receptor subtype 1 (M1) anatgonists.

This Letter describes the synthesis and SAR, developed through an iterative analog library approach, of a novel series of selective M(1) mAChR antagonists, based on an N-(4-(4-alkylpiperazin-1-yl)phenyl)benzamide scaffold for the potential treatment of Parkinsons disease, dystonia and other movement disorders. Compounds in this series possess M(1) antagonist IC(50)s in the 350 nM to >10 microM range with varying degrees of functional selectivity versus M(2)-M(5).

Novel GlyT1 inhibitor chemotypes by scaffold hopping. Part 2. Development of a [3.3.0]-based series and other piperidine bioisosteres

This Letter describes the development and SAR of a novel series of GlyT1 inhibitors derived from a scaffold hopping approach, in lieu of an HTS campaign, which provided intellectual property position. Members within this new [3.3.0]-based series displayed excellent GlyT1 potency, selectivity, free fraction, and modest CNS penetration. Moreover, enantioselective GlyT1 inhibition was observed, within this novel series and a number of other piperidine bioisosteric cores.

Cytochromes P450 1A2 and 3A4 Catalyze the Metabolic Activation of Sunitinib

Sunitinib is a multitargeted tyrosine kinase inhibitor associated with idiosyncratic hepatotoxicity. The mechanisms of this toxicity are unknown. We hypothesized that sunitinib undergoes metabolic activation to form chemically reactive, potentially toxic metabolites which may contribute to development of sunitinib-induced hepatotoxicity. The purpose of this study was to define the role of cytochrome P450 (P450) enzymes in sunitinib bioactivation. Metabolic incubations were performed using individual recombinant P450s, human liver microsomal fractions, and P450-selective chemical inhibitors. Glutathione (GSH) and dansylated GSH were used as trapping agents to detect reactive metabolite formation. Sunitinib metabolites were analyzed by liquid chromatography-tandem mass spectrometry. A putative quinoneimine-GSH conjugate (M5) of sunitinib was detected from trapping studies with GSH and dansyl-GSH in human liver microsomal incubations, and M5 was formed in an NADPH-dependent manner. Recombinant P450 1A2 generated the highest levels of defluorinated sunitinib (M3) and M5, with less formation by P450 3A4 and 2D6. P450 3A4 was the major enzyme forming the primary active metabolite N-desethylsunitinib (M1). In human liver microsomal incubations, P450 3A inhibitor ketoconazole reduced formation of M1 by 88%, while P450 1A2 inhibitor furafylline decreased generation of M5 by 62% compared to control levels. P450 2D6 and P450 3A inhibition also decreased M5 by 54 and 52%, respectively, compared to control. In kinetic assays, recombinant P450 1A2 showed greater efficiency for generation of M3 and M5 compared to that of P450 3A4 and 2D6. Moreover, M5 formation was 2.7-fold more efficient in human liver microsomal preparations from an individual donor with high P450 1A2 activity compared to a donor with low P450 1A2 activity. Collectively, these data suggest that P450 1A2 and 3A4 contribute to oxidative defluorination of sunitinib to generate a reactive, potentially toxic quinoneimine. Factors that alter P450 1A2 and 3A activity may affect patient risk for sunitinib toxicity.