New Clerodane Diterpenes from Fungal Biotransformation of the 3,12-Dioxo-15,16-Epoxy-4-Hydroxycleroda-13(16),14-Diene

Abstract

Abbreviations: PDA, potato-dextrose agar; DMSO, dimethyl sulfoxide; HPLC-DAD, high performance liquid chromatography--diode array detector; ODS, octadecylsilane; FTIR, fourier transform infrared spectroscopy; HRMS, high-resolution mass spectrometer; 1 HNMR, proton nuclear magnetic resonance;13 CNMR, carbon nuclear magnetic resonance; NOESY, nuclear overhauser effect spectroscopy; HSQC, heteronuclear single quantum coherence; HMBC, heteronuclear multiple bond correlation IntroductionTerpenes, with approximately 30,000 compounds, are considered one of the most important classes of natural products isolated from plants. They have high economic value and have applications in several areas such as pharmaceutical and cosmetic industries. Among the terpenes, diterpenes are notable by exhibiting anti-microbial, insecticidal, anti-carcinogenic, anti-diabetic and neurobiological activities.1-3 Microbial transformations of diterpenes have been reported as an alternative tool to furnish new derivatives. 4 Advantages of using this kind of enzyme transformation include high level of regio-and stereo-selectivity, require mild reaction conditions and are important steps to introduce functional groups into inaccessible sites of the molecules, producing rare structures. [3][4][5][6] The clerodane diterpene (3R, 4S, 5S, 8S, 9R, 10S)-3,12-dioxo-15,16-epoxy-4-hydroxycleroda-13(16),14-diene (1) was isolated for the first time from Croton argyrophylloides (Euphorbiaceae). This compound was biotransformed by Cunninghamella echinulata and Rhizopus stolonifer fungi and produced a new diterpene, as previously described by Monte et al. 7 and Mafezoli et al. 8In this work, we report the isolation of one known (B1) and three new diterpenes (B2, B3 and B4) obtained from biotransformation of diterpene 1 by a fungal strain of Lasiodiplodia gonubiensis, Neofusicoccumum ribis and Pseudofusicoccum stromaticum. Additionally, two new chemical derivatives (Q1 and Q2) obtained by esterification and benzylation of B2. The structures of the diterpenes were established mainly based on their 1D and 2D NMR spectroscopic data and HRMS. Materials and methods General procedureMelting points were determined on a Micro-Quimica MQAPF-302 and Mettler Toledo FP62 apparatus, and are uncorrected. IR spectra were recorded on a Perkin-Elmer Spectrum 100 FT-IR spectrometer. Optical rotations were determined on Jasco P-2000 equipment. NMR spectra were recorded on Bruker Avance DPX 300 (300MHz) and Avance DPX 500 (500MHz) spectrometers. High-resolution MS were obtained on a Shimadzu LC-MS IT-TOF spectrometer equipped with an ESI source in positive and negative modes. Analytical thin-layer chromatography (TLC) was performed on pre-coated 0.25mm thick plates of silica gel 60 F254, and the spots were visualized under a UV lamp (254nm) and by spraying with a solution of perchloric acidvanillin in EtOH, followed by heating. HPLC analyses were done on a Shimadzu instrument equipped with a LC-20AT high-pressure pump, a SPD-M20A photodiode array detector. Potato-dextrose-broth w...

Diterpenes from Different Fungal Sources and Their 13C-NMR Data

“…Columbin exhibited dose-dependent anti-inflammatory activity as well as chemopreventive activity against colorectal cancer [26][27][28]. During the last 25 years, over 1300 diterpenoids and nor-diterpenoids with the clerodane carbon skeleton have been isolated [29,30]. The detailed classification of clerodane diterpenes is given in Figure 2.…”

“…Three strains of endophytic fungi L. gonubiensis, N. ribis, and P. stromaticum produced one known and five unknown compounds (B1-B4) through a process of biotransformation, while compounds Q1-Q2 are derived as chemical derivatization of compound 2 [30]. These compounds were actually isolated for the first time from Croton argyrophylloides (Euphorbiaceae)…”

Microbial Transformation of neo-Clerodane Diterpenoid, Scutebarbatine F, by Streptomyces sp. CPCC 205437

“…Structurally, all of the natural clerodane diterpenes were classified as seven different types on the basis of the decalin ring and C-11-C-16 moiety (Supplementary Figure 1; Li et al, 2016). Although more than 1,300 clerodane diterpenoids have been reported, there are a few reports on biotransformation of neoclerodane diterpenes (Hoffmann and Fraga, 1993;Choudhary et al, 2013;Mafezoli et al, 2014;Kumar et al, 2016;Vasconcelos et al, 2017). To the best of our knowledge, there is no report about biotransformation of 13-spiro neo-clerodane diterpenes till now.…”