The main transcriptional regulator of the human immunodeficiency virus, the Tat protein, recognizes and binds to a small structured RNA element at the 5' end of every viral mRNA, termed TAR. On the basis of published structural data of the molecular interactions between TAR and Tat-related peptides, we defined requirements for potential low-molecular weight inhibitors of TAR recognition by the Tat protein. In accordance with the resulting concept, a series of compounds was synthesized. In vitro evaluation of their potential to directly interfere with Tat-TAR interaction was used to define a new chemical class of potent Tat antagonistic substances. The most active compound competed with Tat-TAR complexation with a competition dose CD50 of 22 nM in vitro and blocked HIV expression in a cellular Tat transactivation system with an IC50 of 1.2 microM. The close relation between structural features of the interaction between TAR and a new type of inhibitory agent, "In-PRiNts" (for inhibitor of protein-ribonucleotide sequences), such as CGP 40336A and those of the Tat-TAR complex was confirmed by RNase A footprinting and by two-dimensional NMR. Structural implications for the complex between this class of compounds and TAR RNA will be presented.
Dedicated to Professor Dieter Seebach on the occasion of his 65th birthdayThe total synthesis of (12S,13S)-trans-epothilone A (1a) was achieved based on two different convergent strategies. In a first-generation approach, construction of the C(11)ÀC(12) bond by Pd 0 -catalyzed Negishi-type coupling between the C(12)-to-C(15) trans-vinyl iodide 5 and the C(7)-to-C(11) alkyl iodide 4 preceded the (nonselective) formation of the C(6)ÀC(7) bond by aldol reaction between the C(7)-to-C(15) aldehyde 25 and the dianion derived from the C(1)-to-C(6) acid 3. The lack of selectivity in the aldol step was addressed in a second-generation approach, which involved construction of the C(6)ÀC(7) bond in a highly diastereoselective fashion through reaction between the acetonide-protected C(1)-to-C(6) diol 31 (−Schinzer×s ketone×) and the C(7)-to-C(11) aldehyde 30. As part of this strategy, the C(11)ÀC(12) bond was established subsequent to the critical aldol step and was based on B-alkyl Suzuki coupling between the C(1)-to-C(11) fragment 40 and C(12)-to-C(15) trans-vinyl iodide 5. Both approaches converged at the stage of the 3-O, 7-O-bis-TBS-protected seco acid 27, which was converted to trans-deoxyepothilone A (2) via Yamaguchi macrolactonization and subsequent deprotection. Stereoselective epoxidation of the trans C(12)ÀC(13) bond could be achieved by epoxidation with Oxone ¾ in the presence of the catalyst 1,2 : 4,5-di-O-isopropylidene-l-erythro-2,3-hexodiuro-2,6-pyranose (42a), which provided a 8 : 1 mixture of 1a and its (12R,13R)-epoxide isomer 1b in 27% yield (54% based on recovered starting material). The absolute configuration of 1a was established by X-ray crystallography. Compound 1a is at least equipotent with natural epothilone A in its ability to induce tubulin polymerization and to inhibit the growth of human cancer cell lines in vitro. In contrast, the biological activity of 1b is at least two orders of magnitude lower than that of epothilone A or 1a.Introduction. ± Epothilones A and B (Fig. 1) are the main representatives of a family of bacterial natural products that exhibit potent antiproliferative activity against a broad range of human cancer cell lines. First isolated in 1993 by Reichenbach, Hˆfle, and coworkers [1], these compounds were subsequently shown by Bollag et al. to be microtubule depolymerization inhibitors [2] and, thus, to inhibit human cancer cell growth by the same mechanism of action as the renowned anticancer drug Taxol ¾ (paclitaxel) [3]. At the time of this discovery, epothilones A and B, apart from paclitaxel and its analogs, were the only compounds recognized in the literature to act as microtubule-stabilizing agents 1 ). However, in distinct contrast to paclitaxel, epothilones were found to be equally effective in vitro against drug-sensitive and multidrug-resistant cell lines [2] [5 ± 7], which immediately suggested that epothilone-derived anticancer agents could eventually be useful for the treatment of drug-resistant tumors.
One of the prime merits of NMR as a tool for lead finding in drug discovery research is its sensitivity and robustness to detect weak protein-ligand interactions. This sensitivity allows to build up ligands for a given target in a modular way, by a fragment-based approach. In this approach, two ligands are seperately identified which bind to the target protein generally weakly, but at adjacent binding sites. In a next step, they are chemically linked to produce a high-affinity ligand. This review discusses methods to detect "second-site" ligands that bind to a protein in the presence of a "first-site" ligand, and methods to elucidate structural details on the spatial orientation of both ligands, so that chemical linkage is based on a large piece of experimental information. Published examples from second-site screening and linker design are summarized, and are complemented by previously unpublished in-house examples.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.