Cryptic Species Account for the Seemingly Idiosyncratic Secondary Metabolism ofSarcophyton glaucumSpecimens Collected in Palau

Abstract

Sarcophyton glaucum is one of the most abundant and chemically studied soft corals with over 100 natural products reported in the literature, primarily cembrane diterpenoids. Yet, wide variation in the chemistry observed from S. glaucum over the past 50 years has led to its reputation as a capricious producer of bioactive metabolites. Recent molecular phylogenetic analysis revealed that S. glaucum is not a single species but a complex of at least seven genetically distinct species not distinguishable using traditional taxonomic criteria. We hypothesized that perceived intraspecific chemical variation observed in S. glaucum was actually due to differences between cryptic species (interspecific variation). To test this hypothesis, we collected Sarcophyton samples in Palau, performed molecular phylogenetic analysis, and prepared chemical profiles of sample extracts using gas chromatography-flame ionization detection. Both unsupervised (principal component analysis) and supervised (linear discriminant analysis) statistical analyses of these profiles revealed a strong relationship between cryptic species membership and chemical profiles. Liquid chromatography with tandem mass spectrometry-based analysis using feature-based molecular networking permitted identification of the chemical drivers of this difference between clades, including cembranoid diterpenes (2R,11R,12R)-isosarcophytoxide (5), (2S,11R,12R)-isosarcophytoxide (6), and isosarcophine (7). Our results suggest that early chemical studies of Sarcophyton may have unknowingly conflated different cryptic species of S. glaucum, leading to apparently idiosyncratic chemical variation.

Anti-Inflammatory Cembranoids from a Formosa Soft Coral Sarcophyton cherbonnieri

“…As the marine environment is an important source of bioactive substances, and due to the high chemical diversity and specimen diversity of the Sarcophyton genus [27,28,34,35], it can be expected that new natural products and activities from soft corals of this genus can be continuously discovered in the future.…”

“…Many studies have revealed that soft corals of the genus Sarcophyton are important sources of various types of natural products, some of them with notable bioactivies [25][26][27][28]. Our previous chemical study on Sarcophyton cherbonnieri led to the isolation of six new cembranoids cherbonolides A-E and one biscembranoid bischerbolide peroxide, along with a known compound, isosarcophine [24].…”

“…Compounds 2 and 4 were elucidated as cembranoids possessing an allylic peroxy group. Cembranoids of isosarcophine-type have been reported frequently [24,[27][28][29][30].…”

New Biscembranoids Sardigitolides A–D and Known Cembranoid-Related Compounds from Sarcophyton digitatum: Isolation, Structure Elucidation, and Bioactivities

“…The absolute configurations of 6 , 7 , and analogs have been confirmed in 2019 by Wen et al from the X-ray single crystal diffraction of the same compound 6 , isolated from the soft coral S. trocheliophorum [ 20 ]. Recently, with the development of molecular phylogenetic analysis technology, McFadden et al suggested that S. glacum contained more than seven genetically distinct clades which might be the reason for the continuous discovery of high chemical diversity of secondary metabolites of the soft coral S. glacum [ 38 ]. For the same reason, it is possible that the corals of Sarcophyton genus could generate similar structure biscembranoids as our present study.…”

Terpenoids from Marine Soft Coral of the Genus Xenia in 1977 to 2019

“…This suggested that it might not be suitable to place soft coral belonging to the genus Xenia in a single taxon as their morphological characteristics used for traditional taxonomy are not well reflected in the phylogeny in this genus [68]. A recent study from Maloney and McFadden's group suggested that chemical studies in the last 50 years on soft coral Sarcophyton may have unknowingly comprised different cryptic species of Sarcophyton glaucum, leading to apparently distinctive chemical variation [69]. In the future, such studies should be carried out for soft coral Xenia to gain more understanding of their idiosyncratic chemical variation.…”