ABSTRACT:The structures of TADDOL-like α-conidendrin-based chiral 1,4-diols (LIGNOLs) have been studied at molecular mechanics, Hartree-Fock (HF)/6-31G* and DFT/B3LYP/TZVP level of theory. The molecules included were 1,1-diphenyl, two diastereomers of 1,1,4-triphenyl, 1,1,4,4-tetraphenyl, and 1,1,4,4-tetramethyl 1,4-diol. Several conformers of each molecule were studied thorougly also including the entropy contributions. For the triphenyl 1,4-diols, which can form π − π interactions between phenyl rings, the DFT optimized structures differed significantly from the HF optimized ones. A property for the most stable structures, in addition to the ability to form π − π interactions, seemed to be the possibility to have the aliphatic six-membered ring in a boat conformation. For all of the studied LIGNOLs some conformers were found, where the two OH groups pointed almost to the same direction. By this an intramolecular hydrogen bond can be formed between them. The bridging hydrogen atom falls at the same place as a chelate-bonded metal ion would be situated, as in the case of the analogous molecules, TADDOLs, but only a few of these molecules would be able to work well as ligands for asymmetric catalysis.

Numerous oxidative transformations of lignan structures have been reported in the literature. In this paper we present an overview on the current findings in the field. The focus is put on transformations targeting a specific structure, a specific reaction, or an interconversion of the lignan skeleton. Oxidative transformations related to biosynthesis, antioxidant measurements, and total syntheses are mostly excluded. Non-metal mediated as well as metal mediated oxidations are reported, and mechanisms based on hydrogen abstractions, epoxidations, hydroxylations, and radical reactions are discussed for the transformation and interconversion of lignan structures. Enzymatic oxidations, photooxidation, and electrochemical oxidations are also briefly reported.

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The vast majority of cervical and 75% of oropharyngeal carcinomas are triggered by infection with a type of high-risk oncogenic human papillomavirus (HPV). It is well-known that E6 and E7 oncoproteins are critical for viral-induced cancer, and hence, they represent valuable targets for therapeutic intervention in HPV-mediated cancers. Our earlier research on the cembranoid, anisomelic acid (AA) showed that, AA has the potential to induce apoptosis in HPV cells by the depletion of E6 and E7 oncoproteins. The present study describes the structure-activity relationship and the evaluation of synthetic AA like compounds, i.e simplified cembranoid-like structures, as HPV inhibitors against some papilloma cell lines. Both from experimental and computational results, we observed that these compounds induced apoptosis by the same E6/E7-based mechanism as AA, but at earlier time points, thus being far more effective than AA. Further, the data indicated that only part of the structure of AA is required for the molecular action. Based on these results, we identified some novel and potential compounds for specific treatment of HPV-associated carcinomas.

General Methods. Unless otherwise stated, chemicals were obtained from commercial suppliers and used without further purification. THF was dried by the sodium-benzophenone method immediately prior to use. NMR spectra were recorded with Bruker Avance 600 MHz and Bruker Avance 500 MHz NMR spectrometers using standard pulse sequences. HRMS were recorded using a Bruker Micro Q-TOF instrument with ESI (electorspray ionization) operated in positive or negative mode. The reactions were monitored by TLC. Aluminum based TLC plates (Merck) silicagel 60 F 254 were used.

Methods for synthetic modifications of the natural dibenzylbutyrolactone lignan hydroxymatairesinol into chiral 1,4-diols with different lignan-derived backbones have been developed. A stepwise procedure, involving alkylation and oxidation, was shown to be successful and several highly substituted 1,4-diols were prepared. Some substituted butyrolactones resisted alkylation and led to the formation unusually stable hemiketals (butyrolactols). The formation of stable hemiketals was investigated in detail, showing that different backbone structures influence the formation and reactivity of the hemiketals.