Chemical Review of Gorgostane-Type Steroids Isolated from Marine Organisms and Their 13C-NMR Spectroscopic Data Characteristics

Gorgostane steroids are isolated from marine organisms and consist of 30 carbon atoms with a characteristic cyclopropane moiety. From the pioneering results to the end of 2021, isolation, biosynthesis, and structural elucidation using 13C-NMR will be used. Overall, 75 compounds are categorized into five major groups: gorgost-5-ene, 5,6-epoxygorgostane, 5,6-dihydroxygorgostane, 9,11-secogorgostane, and 23-demethylgorgostane, in addition to miscellaneous gorgostane. The structural diversity, selectivity for marine organisms, and biological effects of gorgostane steroids have generated considerable interest in the field of drug discovery research.


Introduction
Marine natural products are an untapped reservoir for discovering biologically active phytomolecules, with a significant array of bioactivities reported against many aliments [1,2]. Antibiotic, antifungal, anti-viral, cytotoxic, and anti-tumor activities are among the reported pharmacological effects of marine-derived molecules [3,4]. Marine organisms have been considered an extraordinarily rich source of new sterols with a core ring system, side chains, and unusual oxygenation patterns on their A-D rings [5][6][7][8]. The origin of these marine invertebrates' sterols is complicated because they may be formed from dietary origins or synthesized by a symbiont and later modified biochemically in the invertebrate [9]. Marine organisms have yielded many sterol metabolites with unusual side chains [10].
Gorgosterol was the first sterol reported to contain a cyclopropane ring on the side chain, and since then, several additional sterols with this ring structure and sterols with polyoxygenated functionalities have been isolated [10]. The reported gorgostane-type steroids from marine organisms possess certain biological activities, including anti-inflammatory activity reported in stoloniferone S isolated from soft coral Clavularia viridis [11], antibacterial and antifungal activities in the in vitro bioassay reported in 11α-acetoxy-gorgostane-3β,5α,6β,12α-tetraol and 12α-acetoxy-gorgostane-3β,5α,6β,11α-tetraol isolated from soft coral Sarcophyton species [12], and cytotoxic activity reported in klyflaccisteroids C-F isolated from soft coral Klyxum flaccidum [13].
Gorgostane-type steroids have some structural variability in the number of carbon atoms and the degree of oxygenation patterns. According to the number of carbon atoms and structural features, gorgostane-type steroids can be classified into five groups. In this

Biosynthesis of Gorgostane Steroids
Sterols with side chains containing the 22,23-cyclopropane group have been encountered only in soft corals that live symbiotically with zooxanthellae. Several experiments were performed to explain the biosynthetic pathways of gorgosterols [52] using the cellfree extracts of the dinoflagellates Peridinium foliaceum, Crypthecodinium cohnii, and the cultured zooxanthella symbiont of Cassiopea xamachana. They found that a decrease in Sadenosylmethionine concentration concomitantly with an increase in dimethylpropiothetin biosynthesis is linked with the attenuation of the production of gorgosterol in aposymbiotic zooxanthellae [53]. In another study, the pseudoplexaurids Pseudoplexaura porosa, P. flagellosa, and P. wagenaari and Pseudopterogorgia americana soft corals were used as a source of zooxanthellae to detect the conversion of labelled farnesyl pyrophosphate to squalene. They concluded that zooxanthellae obtained from P. porosa contributed to the part of the pathway from mevalonate to gorgosterol (Figure 1) that encloses the formation of squalene [54].

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biosynthesis is linked with the attenuation of the production of gorgosterol in aposymbiotic zooxanthellae [53]. In another study, the pseudoplexaurids Pseudoplexaura porosa, P. flagellosa, and P. wagenaari and Pseudopterogorgia americana soft corals were used as a source of zooxanthellae to detect the conversion of labelled farnesyl pyrophosphate to squalene. They concluded that zooxanthellae obtained from P. porosa contributed to the part of the pathway from mevalonate to gorgosterol (Figure 1) that encloses the formation of squalene [54].

Gorgostane Steroids
Gorgostane is a steroid with a basic molecular formula of C30 H52 ( Figure 2). Most are pentacyclic, with the exception of secogorgosterols, which are tetracyclic steroids. Both gorgosterol and secogorgosterol have a side chain containing a characteristic cyclopropane moiety. The cyclopropane moiety of the gorgostane steroid (C-22, C-23, and C-30) showed characteristic signals in 13 C NMR at 32.1, 25.8, and 21.3 ppm, respectively. According to the number of rings, the presence and position of unsaturation, and the number of substituents, gorgostane can be classified into different groups.

Gorgostane Steroids
Gorgostane is a steroid with a basic molecular formula of C 30 H 52 ( Figure 2). Most are pentacyclic, with the exception of secogorgosterols, which are tetracyclic steroids. Both gorgosterol and secogorgosterol have a side chain containing a characteristic cyclopropane moiety. The cyclopropane moiety of the gorgostane steroid (C-22, C-23, and C-30) showed characteristic signals in 13 C NMR at 32.1, 25.8, and 21.3 ppm, respectively. According to the number of rings, the presence and position of unsaturation, and the number of substituents, gorgostane can be classified into different groups.

Conclusions
This review provides an exploration of the structural diversity of gorgostane-type steroids isolated from marine sources and 13 C-NMR spectroscopic data, which are considered an added value to the structural identification of gorgostane derivatives. Further investigation of this class of biological activity explaining its mechanisms of action in treating different diseases is required. These studies will assist in the discovery and development of new drugs from natural sources.