Efficient Synthetic Methodology for the Construction of Dihydronaphthalene and Benzosuberene Molecular Frameworks.

Benzosuberene analogues (1 and 2) and dihydronaphthalene analogues (3 and 4) function as potent inhibitors of tubulin polymerization, demonstrate pronounced cytotoxicity (low nM to pM range) against human cancer cell lines, and are promising vascular disrupting agents (VDAs). As such, these compounds represent lead anticancer agents with potential translatability towards the clinic. Methodology previously established by us (and others) facilitated synthetic access to a variety of structural and functional group modifications necessary to explore structure activity relationship considerations directed towards the development of these (and related) molecules as potential therapeutic agents. During the course of these studies it became apparent that the availability of synthetic methodology to facilitate direct conversion of the phenolic-based compounds to their corresponding aniline congeners would be beneficial. Accordingly, modified synthetic routes toward these target phenols (benzosuberene 1 and dihydronaphthalene 3) were developed in order to improve scalability and overall yield [45-57% (1) and 32% (3)]. Moreover, benzosuberene-based phenolic analogue 1 and separately dihydronaphthalene-based phenolic analogue 3 were successfully converted into their corresponding aniline analogues 2 and 4 in good yield (>60% over three steps) using a palladium catalyzed amination reaction.

Structural interrogation of benzosuberene-based inhibitors of tubulin polymerization.

The discovery of 3-methoxy-9-(30,40,50-trimethoxyphenyl)-6,7-dihydro-5H-benzo[7]annulen-4-ol (a benzosuberene-based analogue referred to as KGP18) was originally inspired by the natural products colchicine and combretastatin A-4 (CA4). The relative structural simplicity and ease of synthesis of KGP18, coupled with its potent biological activity as an inhibitor of tubulin polymerization and its cytotoxicity (in vitro) against human cancer cell lines, has resulted in studies focused on new analogue design and synthesis. Our goal was to probe the relationship of structure to function in this class of anticancer agents. A series of twenty-two new benzosuberene-based analogues of KGP18 was designed and synthesized. These compounds vary in their methoxylation pattern and separately incorporate trifluoromethyl groups around the pendant aryl ring for the evaluation of the effect of functional group modifications on the fused six-membered aromatic ring. In addition, the 8,9-saturated congener of KGP18 has been synthesized to assess the necessity of unsaturation at the carbon atom bearing the pendant aryl ring. Six of the molecules from this benzosuberene-series of compounds were active (IC50 < 5 lM) as inhibitors of tubulin polymerization while four analogues were comparable (IC50 approximately 1 lM) in their tubulin inhibitory activity to CA4 and KGP18. The potency of a bis-trifluoromethyl analogue 74 and the unsaturated KGP18 derivative 73 as inhibitors of tubulin assembly along with their moderate cytotoxicity suggested the potential utility of these compounds as vascular disrupting agents (VDAs) to selectively target microvessels feeding tumors. Accordingly, water-soluble and DMSO-soluble phosphate prodrug salts of each were synthesized for preliminary in vivo studies to assess their potential efficacy as VDAs.

Covalent Inhibition of Wild-Type HIV-1 Reverse Transcriptase Using a Fluorosulfate Warhead.

Covalent inhibitors of wild-type HIV-1 reverse transcriptase (CRTIs) are reported. Three compounds derived from catechol diether non-nucleoside inhibitors (NNRTIs) with addition of a fluorosulfate warhead are demonstrated to covalently modify Tyr181 of HIV-RT. X-ray crystal structures for complexes of the CRTIs with the enzyme are provided, which fully demonstrate the covalent attachment, and confirmation is provided by appropriate mass shifts in ESI-TOF mass spectra. The three CRTIs and six noncovalent analogues are found to be potent inhibitors with both IC50 values for in vitro inhibition of WT RT and EC50 values for cytopathic protection of HIV-1-infected human T-cells in the 5-320 nM range.

Structure Guided Design, Synthesis, and Biological Evaluation of Novel Benzosuberene Analogues as Inhibitors of Tubulin Polymerization.

A promising design paradigm for small-molecule inhibitors of tubulin polymerization that bind to the colchicine site draws structural inspiration from the natural products colchicine and combretastatin A-4 (CA4). Our previous studies with benzocycloalkenyl and heteroaromatic ring systems yielded promising inhibitors with dihydronaphthalene and benzosuberene analogues featuring phenolic (KGP03 and KGP18) and aniline (KGP05 and KGP156) congeners emerging as lead agents. These molecules demonstrated dual mechanism of action, functioning both as potent vascular disrupting agents (VDAs) and as highly cytotoxic anticancer agents. A further series of analogues was designed to extend functional group diversity and investigate regioisomeric tolerance. Ten new molecules were effective inhibitors of tubulin polymerization (IC50 < 5 µM) with seven of these exhibiting highly potent activity comparable to CA4, KGP18, and KGP03. For one of the most effective agents, dose-dependent vascular shutdown was demonstrated using dynamic bioluminescence imaging in a human prostate tumor xenograft growing in a rat.