Marine Streptomyces sp. derived antimycin analogues suppress HeLa cells via depletion HPV E6/E7 mediated by ROS-dependent ubiquitin-proteasome system.

Four new antimycin alkaloids (1-4) and six related known analogs (5-10) were isolated from the culture of a marine derived Streptomyces sp. THS-55, and their structures were elucidated by extensive spectroscopic analysis. All of the compounds exhibited potent cytotoxicity in vitro against HPV-transformed HeLa cell line. Among them, compounds 6-7 were derived as natural products for the first time, and compound 5 (NADA) showed the highest potency. NADA inhibited the proliferation, arrested cell cycle distribution, and triggered apoptosis in HeLa cancer cells. Our molecular mechanic studies revealed NADA degraded the levels of E6/E7 oncoproteins through ROS-mediated ubiquitin-dependent proteasome system activation. This is the first report that demonstrates antimycin alkaloids analogue induces the degradation of high-risk HPV E6/E7 oncoproteins and finally induces apoptosis in cervical cancer cells. The present work suggested that these analogues could serve as lead compounds for the development of HPV-infected cervical cancer therapeutic agents, as well as research tools for the study of E6/E7 functions.

Donor-acceptor substituted cyclopropane to butanolide and butenolide natural products: enantiospecific first total synthesis of (+)-hydroxyancepsenolide.

An oxygen substituted donor-acceptor cyclopropane (DAC) is used as a common intermediate in the enantiospecific collective total synthesis of butanolide- and butenolide-based natural products like (+)-juruenolide C and D, (+)-blastmycinone, (+)-antimycinone, and (+)-ancepsenolide. Enantiospecific first total syntheses of (+)-hydroxyancepsenolide and its acetate are achieved confirming their absolute stereochemistry.

Organoboron-based allylation approach to the total synthesis of the medium-ring dilactone (+)-antimycin A(1b).

The stereoselective synthesis of (+)-antimycin A1b has been accomplished in 12 linear steps and 18% overall yield from (-)-ethyl lactate. A robust, scalable, and highly diastereoselective montmorillonite K10-promoted allylation reaction between an α-silyloxy aldehyde and a substituted potassium allyltrifluoroborate salt provides a general approach to the core stereochemical triad of the antimycin A family. The requisite (Z)-substituted potassium allyltrifluoroborate salt was synthesized using a syn-selective hydroboration/protodeboration of an alkynylboronate ester, followed by a Matteson homologation reaction. The total synthesis leverages an MNBA (Shiina's reagent)-mediated macrolactonization to generate the 9-membered dilactone ring and a late-stage PyBOP-mediated amide coupling employing an unprotected 3-formamidosalicylic acid fragment, thereby shortening the longest linear sequence and, perhaps most notably, generating the antimycin A C7-C8-C9 stereotriad in a single step using a single chiral pool-derived stereocenter.

An organotrifluoroborate-based convergent total synthesis of the potent cancer cell growth inhibitory depsipeptides kitastatin and respirantin.

The total syntheses of the highly cytotoxic neo-antimycin macrocyclic depsipeptide natural products kitastatin and respirantin have been accomplished in a convergent manner using MNBA promoted esterifications and an efficient C- and N-terminus bis-deprotection/HATU promoted macrolactamization. The first examples of using a prenyltrifluoroborate reagent in additions to carbonyl groups are disclosed including a diastereoselective multigram scale montmorillonite K10 catalyzed prenylation of N-Boc-l-leucinal to install the structurally unique gem-dimethyl-ß-keto-ester fragment.

Enzymatic synthesis of dilactone scaffold of antimycins.

Antimycins are a family of natural products possessing outstanding biological activities and unique structures, which have intrigued chemists for over a half century. The antimycin structural skeleton is built on a nine-membered dilactone ring containing one alkyl, one acyloxy, two methyl moieties, and an amide linkage connecting to a 3-formamidosalicylic acid. Although a biosynthetic gene cluster for antimycins was recently identified, the enzymatic logic that governs the synthesis of antimycins has not yet been revealed. In this work, the biosynthetic pathway for antimycins was dissected by both genetic and enzymatic studies for the first time. A minimum set of enzymes needed for generation of the antimycin dilactone scaffold were identified, featuring a hybrid nonribosomal peptide synthetase (NRPS)-polyketide synthase (PKS) assembly line containing both cis- and trans-acting components. Several antimycin analogues were further produced using in vitro enzymatic total synthesis based on the substrate promiscuity of this NRPS-PKS machinery.

A practical total synthesis of (+)-antimycin A9.

(+)-Antimycin A9 (AA9) isolated from a cultured broth of Streptomyces sp. K01-0031 was synthesized via an asymmetric aldol reaction using Oppolzer's sultam as a chiral auxiliary.

Potent inhibitors of the Qi site of the mitochondrial respiration complex III.

A series of azole-fused salicylamides were prepared as analogues of antimycin and assayed for activity at complex III of the mitochondrial respiratory chain. The activity of these compounds approached that of antimycin in inhibitory potency and some showed growth reduction of Septoria nodorum in vitro. Compound 8a was shown to bind at the Qi site of complex III by red-shift titration of the bc1 complex.

An expeditious enantioselective synthesis of antimycin A3b.

A straightforward enantioselective route to (+)-antimycin A3b is presented, which used a TiCl4-mediated asymmetric aldolization to construct C-7/C-8 and BnOH/DMAP to remove the chiral auxiliary with concurrent protection of the carboxylic group, respectively. Closing the dilactone ring was achieved in 62% yield (previously 0.8%, 13.4%, or 20%) in the presence of the C-8 ester functionality. The overall yield (34.5%) was significantly higher than that (0.019-3.6%) of the earlier routes.

Structural factors of antimycin A molecule required for inhibitory action.

A series of antimycin A analogues was synthesized by modifying the salicylic acid moiety, whereas the portion of the molecule corresponding to the natural dilactone-ring moiety was fixed as di-n-octyl L-glutamate. To probe the structure of the antimycin A binding site, the structural factors of the salicylic acid moiety required for inhibitory action were examined by means of structure-activity studies with intact rat-liver mitochondria and the cytochrome bc1 complex isolated from bovine heart mitochondria. As suggested earlier (Rieske, J.S. (1976) Biochim. Biophys. Acta 456, 195-247), the phenolic OH was very important for inhibition. For the derivatives which do not possess a formylamino group in the 3-position (ortho to the phenolic OH), the inhibitory activity tended to increase as the electron-withdrawing property of the substituent increased, i.e., as the acidity of the phenolic OH group increased. This indicates that the acidity of the phenolic OH is an important factor governing inhibition. While the electron-withdrawing property of the formylamino group itself is rather poor, 3-formylamino derivatives elicited potent activity. The conformation of the 3-formylamino group was also found to be a very important factor in establishing inhibitory activity. In addition, the bulkier the moiety corresponding to the 3-formylamino group, the lower the activity. These results demonstrate that the presence of the 3-formylamino group, and its proper conformation, are needed for a close fitting of antimycin A to its binding domain. Although the inhibitors that lack a 3-formylamino group retained fairly potent activity, their effects on the reduction of cytochromes b and c1 were somewhat different from those of natural antimycin A, indicating that the 3-formylamino group is essential for inhibitor binding to the cytochrome bc1 complex in the same manner as natural antimycin A. It is concluded that both the 3-formylamino group and the phenolic OH of antimycin A make important contributions to specific interactions with the amino acid residues of the cytochrome b.

Structure-activity relationships of antifilarial antimycin analogues: a multivariate pattern recognition study.

The structure-activity relationships of a series of novel antifilarial antimycin A1 analogues have been investigated by using computational chemistry and multivariate statistical techniques. The physiochemical descriptors calculated in this way contained information which was useful in the classification of compounds according to their in vitro antifilarial activity. This approach generated a 53 parameter descriptor set, which was reduced with a multivariate pattern recognition package, ARTHUR. Regression analysis of the reduced set yielded several statistically significant regression equations; e.g.-log in vitro activity = 0.017 mp + 0.65 log P - 0.81ESDL10-7.33 (R = 0.9). With use of this equation, it was possible to make predictions for further untested analogues. The analysis indicated that membrane or lipid solubility is an important determinant in biological activity agreeing with the proposed primary mode of action of the compounds as disrupters of cuticular glucose uptake.