Resveratrol oligomer structure in Dipterocarpaceaeous plants
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REVIEW
Resveratrol oligomer structure in Dipterocarpaceaeous plants Tetsuro Ito1,2 Received: 2 March 2020 / Accepted: 10 April 2020 © The Japanese Society of Pharmacognosy 2020
Abstract Oligostilbenoids are a group of natural products derived from the oxidative coupling of C6–C2–C6 units found in some plant families. A structurally diverse chemical pool is produced after the successive regioselective and stereoselective oligomerization of resveratrol. This review describes the current status and knowledge of the structure of resveratrol oligomers (ROs) in Dipterocarpaceaeous plants (DPs). Beginning with the recently validated formation of ROs in DPs, each downstream conversion is described from the perspective of the resveratrol coupling mode. Particular emphasis is placed upon the regioselectivity of monomer- and dimer-derived radical–radical coupling processes, which are responsible for producing dimers, trimers, and tetramers with various cyclic frame skeletons, as well as related processes that result in highly condensed scaffolds, such as hexamers and octamers. Trimers in oxidized, dearomatized, and rearranged forms are also summarized, as well as the biogenic relationship between the compounds. Furthermore, emphasis is placed on the O- and C-glucosides of ROs, as well as on the hetero-coupled ROs. In addition, several stereoisomers that originate from asymmetric carbons and the stereochemistry with respect to the conformation due to the chiral axis are described. Besides, NMR spectroscopic properties such as coalescence and anisotropy are briefly described. Approaches to determine absolute configuration are also summarized. Keywords Dipterocarpaceae · Resveratrol · Oligomerization · Structural diversity
Introduction In the plant kingdom, resveratrol oligomers (ROs) can be found in a number of plant families, such as the Dipterocarpaceae, Vitaceae, Cyperaceae, Fabaceae, Paeoniaceae, and Gnetaceae families [1–4]. The Dipterocarpaceaeous plant (DP) is the dominant plant family of Southeast Asia, with a total of 470 species [5, 6]. Indeed, plants in this family are a rich source of ROs, which are produced from the successive condensation of resveratrol (1: trans3,5,4′-trihydroxystilbene) (Fig. 1). The first RO was characterized from Hopea odorata in 1966 [7]; in the following 25 years, dozens of structurally related compounds have
* Tetsuro Ito tito@u‑gifu‑ms.ac.jp 1
Laboratory of Pharmacognosy, Gifu Pharmaceutical University, 1‑25‑4 Daigaku‑nishi, Gifu 501‑1196, Japan
Present Address: Laboratory of Pharmacognosy, Department of Pharmacy, Faculty of Pharmacy, Gifu University of Medical Science, 4‑3‑3 Nijigaoka, Kani, Gifu 509‑0293, Japan
2
been identified [1]. In recent years, several hundred ROs have been isolated from DPs with their structures determined accordingly [2]. In essence, this structural diversity stems from patterns of phenoxy radical–radical coupling that yield various fused-ring systems containing asymmetric carbons, which, in turn, give rise to regioisomerism and stereoisomerism. S
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