Stereochemistries and Biological Properties of Oligomycin A Diels-Alder Adducts.

Oligomycin A is a potent antibiotic and antitumor agent. However, its applications are restricted by its high toxicity and low bioavailability. In this study, we obtained Oligomycin A Diels-Alder adducts with benzoquinone and N-benzylmaleimide and determined their absolute configurations by combining 1H and ROESY NMR data with molecular mechanics conformational analysis and quantum chemical reaction modeling. The latter showed that adduct stereochemistry is controlled by hydrogen bonding of the Oligomycin A side-chain isopropanol moiety with the carbonyl group of the dienophile. Biological studies showed that the Diels-Alder modification of the Oligomycin A diene system resulted in a complex antiproliferative potential pattern. The synthesized adducts were determined to be more active against the triple-negative (ERα, PR, and HER2 negative) breast cancer cell line MDA-MB-231 and lung carcinoma cell line A-549 compared to Oligomycin A. Meanwhile, Oligomycin A was more potent against myeloid leukemia cell line K-562 and breast carcinoma cell line MCF-7 than its derivatives. Thus, modification of the diene moiety of Oligomycin A is a promising strategy for developing novel antitumor agents based on its scaffold.

Synthesis, antimicrobial and antiproliferative properties of epi-oligomycin A, the (33S)-diastereomer of oligomycin A.

We describe the synthesis of epi-oligomycin A, a (33S)-diastereomer of the antibiotic oligomycin A. The structure of (33S)-oligomycin A was determined by elemental analysis, spectroscopic studies, including 1D and 2D NMR spectroscopy, and mass spectrometry. Isomerization of C33 hydroxyl group led to minor changes in the potency against Aspergillus niger, Candida spp., and filamentous fungi whereas the activity against Streptomyces fradiae decreased by approximately 20-fold compared to oligomycin A. We observed that 33-epi-oligomycin A had the same activity on the human leukemia cell line K562 as oligomycin A but was more potent for the multidrug resistant subline K562/4. Non-malignant cells were less sensitive to both oligomycin isomers. Finally, our results pointed at the dependence of the cytotoxicity of oligomycins on oxygen supply.

Verification of oligomycin A structure: synthesis and biological evaluation of 33-dehydrooligomycin A.

Although, the structure of oligomycin A (1) was confirmed by spectroscopic and chemical evaluations, some crystallographic data cast doubt on the originally adopted structure of the side 2-hydroxypropyl moiety of this antibiotic. It was suggested that the side chain of the oligomycin is enol-related (2-hydroxy-1-propenyl). To clarify this matter we synthesized and evaluated 33-dehydrooligomycin A (2) prepared by the Kornblum oxidation of 33-O-mesyloligomycin A (3) by dimethyl sulfoxide. NMR data for 33-dehydrooligomycin (2) and results of quantum chemical calculations have shown that this derivative exists in the keto rather than in the enol tautomer 2a. The in vitro antimicrobial activity of 2 was approximately two times weaker in comparison with oligomycin A against Streptomyces fradiae ATCC-19609 and reference Candida spp. strains and similar activity against certain filamentous fungi. The docking binding estimate of 2 with FOF1ATP synthase showed a slight decrease in binding affinity for 2 when compared with oligomycin A; that correlated with its activity against S. fradiae ATCC 19609 that is supersensitive to oligomycin A. The in vitro antiproliferative activities of 2 are also discussed.

Study on retroaldol degradation products of antibiotic oligomycin A.

Studies of reactivity of antibiotic oligomycin A in various alkaline conditions showed that the compound easily undergoes retroaldol degradation in ß-hydroxy ketone fragments positioned in the C7-C13 moiety of the antibiotic molecule. Depending on reaction conditions, the retroaldol fragmentation of the 8,9 or 12,13 bonds or formation of a product through double retroaldol degradation, when the fragment C9-C12 was detached, took place followed by further transformations of the intermediate aldehydes formed. The structures of the obtained non-cyclic derivatives of oligomycin A were supported by NMR and MS methods. NMR parameters demonstrate the striking similarity of the geometry (conformation) of the fragment C20-C34 in the non-cyclic products of retroaldol degradation and the starting antibiotic 1. The compounds obtained had lower cytototoxic properties than oligomycin A for human leukemia cells K-562 and colon cancer cells HCT-116 and lower activity against growth inhibition of model object Streptomyces fradiae. It cannot be excluded that the products of retroaldol degradation participate in the biological effects of antibiotic oligomycin A.

Synthesis and cytotoxicity of oligomycin A derivatives modified in the side chain.

A novel way of chemical modification of the macrolide antibiotic oligomycin A (1) at the side chain was developed. Mesylation of 1 with methane sulfonyl chloride in the presence of 4-dimethylaminopyridine produced 33-O-mesyl oligomycin in 56% yield. Reactions of this intermediate with sodium azide produced the key derivative 33-azido-33-deoxy-oligomycin A in 60% yield. 1,3-Dipolar cycloaddition reaction with propiolic acid, methyl ester of propiolic acid, and phenyl acetylene resulted in 33-deoxy-33-(1,2,3-triazol-1-yl)oligomycin A derivatives substituted at N4 of the triazole cycle. The mesylated oligomycin A and 33-deoxy-33-azidooligomycin A did not inhibit F0F1 ATFase ATPase; however, 33-azido-33-deoxy-oligomycin A and the derivatives containing 4-phenyltriazole, 4-methoxycarbonyl-triazole and 3-dimethylaminoethyl amide of carboxyltriazole substituents demonstrated a high cytotoxicity against K562 leukemia and HCT116 human colon carcinoma cell lines whereas non-malignant skin fibroblasts were less sensitive to these compounds. Novel series of oligomycin A derivatives allow for the search of intracellular molecules beyond F0F1 ATP synthase relevant to the cytotoxic properties of this perspective chemical class.

A novel acyclic oligomycin A derivative formed via retro-aldol rearrangement of oligomycin A.

The antibiotic oligomycin A in the presence of K(2)CO(3) and n-Bu(4)NHSO(4) in chloroform in phase-transfer conditions afforded a novel derivative through the initial retro-aldol fragmentation of the 8,9 bond, followed by further transformation of the intermediate aldehyde. NMR, MS and quantum chemical calculations showed that the novel compound is the acyclic oligomycin A derivative, in which the 8,9 carbon bond is disrupted and two polyfunctional branches are connected with spiroketal moiety in positions C-23 and C-25. The tri-O-acetyl derivative of the novel derivative was prepared. The acyclic oligomycin A derivative retained the ability to induce apoptosis in tumor cells at low micromolar concentrations, whereas its antimicrobial potencies decreased substantially. The derivative virtually lost the inhibitory activity against F(0)F(1) ATP synthase-containing proteoliposomes, strongly suggesting the existence of the target(s) beyond F(0)F(1) ATP synthase that is important for the antitumor potency of oligomycin A.

The first examples of chemical modification of oligomycin A.

The first examples of chemical modification of antibiotic oligomycin A are described. The interaction of oligomycin A with hydroxylamine yielded six-membered nitrone annelated with the antibiotic at the positions 3,4,5,6,7. The reaction with 1-aminopyridinium iodide in pyridine led to pyrazolo[1,5-a]pyridine conjugated with the antibiotic at the positions 2 and 3 (product of addition to the C(2)-C(3) double bond followed by spontaneous oxidation). The structures of the compounds obtained were supported by NMR and mass spectrometry methods including the (15)N-labeling of compounds.