A Brief Review on New Naturally Occurring Cembranoid Diterpene Derivatives from the Soft Corals of the Genera Sarcophyton, Sinularia, and Lobophytum Since 2016

This work reviews the new isolated cembranoid derivatives from species of the genera Sarcophyton, Sinularia, and Lobophytum as well as their biological properties, during 2016–2018. The compilation permitted to conclude that much more new cembranoid diterpenes were found in the soft corals of the genus Sarcophyton than in those belonging to the genera Lobophytum or Sinularia. Beyond the chemical composition, the biological properties were also reviewed, namely anti-microbial against several Gram-positive and Gram-negative bacteria and fungi, anti-inflammatory and anti-tumoral against several types of cancer cells. In spite of the biological activities detected in almost all samples, there is a remarkable diversity in the results which may be attributed to the chemical variability that needs to be deepened in order to develop new molecules with potential application in medicine.


Introduction
The cembrane skeleton is isoprenoid and consists of a fourteen-membered carbocyclic ring with an isopropyl residue at position 1 and three methyl groups at positions 4, 8, and 12 ( Figure 1). The basic structure of this diterpene usually presents cyclic ether, lactone, or furan moieties around the macrocyclic ring. There are also cembranoids variants which contain a 12 or 13-membered carbon skeleton [1][2][3].
Soft corals (phylum, Cnidaria; class, Anthozoa; subclass, Octocorallia; order, Alcyonaceae; family, Alcyoniidae) have been the target of study since the nineteenth century. The subclass Octocorallia includes soft corals, gorgonians, and sea pens. Most soft corals belong to the order Alcyonacea that comprises several families, including Alcyoniidae. This family contains the genera Sarcophyton, Sinularia, and Lobophytum [8]. Soft corals are found in Indo Pacific reefs whereas Gorgonian octocorals In nature, cembranoids may act as chemical defense compounds against fish predators and/or competing for reef organisms, bacteria, parasites, to ensure their protection and survival [7,9]. Multiple in vitro biological properties of cembranoids of marine origin have been reported such as anti-inflammatory, anti-tumoral, anti-bacterial, anti-viral, neuroprotective, antiarthritic, calcium-antagonistic, and cytotoxic [9,10]. This is the first step for the in vivo assays which will determine whether or not they constitute potential therapeutic agents.
Yang et al. [10] review all the metabolites of cembrane diterpenes either from terrestrial or marine organisms up to 2010. They were divided into several different families according to the variety of ring sizes, oxidation patterns, and the respective biological activities. Several other reviews have been made regarding new compounds and their biological activities. These compounds have been isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, mollusks, tunicates, echinoderms, mangroves and other intertidal plants, from 2013 until 2017 [11][12][13][14]. Marine invertebrates isolated from soft corals of the genera Sinularia, Lobophytum, Eunicea, and Sarcophyton are also included in these reviews.
The present work will review the new cembranoid diterpenes isolated from species belonging to the family Alcyoniidae, which contains the genera Sarcophyton, Sinularia, and Lobophytum as well as their biological properties, since 2016. For this review, only the Web of Science was used as a database for research by utilizing the keywords cembrane, and cembranoid.

Chemical Structure of Cembranoids from Marine Origin
According to Rodríguez et al. [16], the cembrane skeleton of marine origin is derived from the cyclization of geranylgeranyl pyrophosphate. This hypothesis is based on the fact that the double bonds of the cembrane skeleton have the geometry E which is observed in geranylgeraniol.
Cembrane diterpenoids have diverse structural variations with a multitude of functional groups (lactone, epoxide, furan, ester, aldehyde, hydroxyl, carboxyl moieties) and cyclizations, which permit to group them in several families [10,17]. According to the review of Yang et al. [10], the cembrane-type diterpenoids may be classified as depicted in Table 1.
Cembranolides possess a 14-membered carbocyclic nucleus, generally fused to a 5-, 6-, 7-, or 8-membered lactone ring. Furanocembranoids possess a 14-membered carbocyclic nucleus as well as a furan heterocycle. They also have a butenolide moiety involving C-10-C-12, and C-20. Biscembranoids possess a 14-6-14 membered tricyclic backbone of tetraterpenoids [10]. The structure of polymaxenolide (13) comprises a 14-membered cembranoid skeleton linked via a spiro ring system, to an africanane skeleton (Table 1) [18].            There are also the polycyclic norcembranoid diterpenes, rare and found exclusively in soft corals of the genus Sinularia. These diterpenes are within the family of furanecembranoids which lack a C-18 carbon substituent in comparison with C20-cembranoids. They co-occur with 14-membered macrocyclic norcembranoids with a furan heterocycle in which also lacks a C-18 carbon substituent [19]. The mechanisms leading to the occurrence of norcembranoid diterpenes are not well understood but they may include the production of anionic and radical intermediates along with competitive transannular carbon-to-carbon bond-forming reactions. However, these are only proposals that, according to the authors [19], must be validated in forthcoming biosynthetic studies.
The extraction of cembranoid diterpenes was generally made with organic solvents (acetone, chloroform, ethanol, ethyl acetate, methanol, and methylene chloride) by maceration (Tables 2-4), followed by the concentration under vacuum. Afterwards, the residue is partitioned between pairs of solvents and further column chromatography eluting with a gradient of solvents with increasing polarity. Different fractions originate the cembranoid compounds, which can be subjected to semior preparative HPLC (high performance liquid chromatography). The identification of compounds is generally made through 1 H-NMR (proton nuclear magnetic resonance), 13 C-NMR (Carbon-13 nuclear magnetic resonance), one dimensional and two dimensional nuclear magnetic resonance (1D-NMR and 2D-NMR) including 1 H-1 H COSY, HMQC, HMBC, and NOESY spectra (Correlation Spectroscopy, Heteronuclear Multiple-Quantum Correlation, Heteronuclear Multiple-Bond Correlation Spectroscopy, Nuclear Overhauser Effect Spectroscopy, respectively), Time-Dependent Density Functional Theory Electronic Circular Dichroism (TDDFT/ECD), Density Functional Theory (DFT)/NMR calculations, FTIR (Fourier-transform infrared spectrosocopy), single crystal X-ray diffraction, and LC-MS-IT-TOF (liquid chromatography-mass spectrometry-ion trap-time-of-flight) [9,.
The review upon the source, chemistry and bioactivities of new cembrane diterpenes from marine organisms, since 2016 (27 works) (Tables 2-4) revealed that the most important sources of cembrane derivatives found in that period were coming from the genus Sarcophyton (14 works), Sinalarina (8 works) and Lobophytum (5 works). There is still one work in which the authors did not isolate new cembrane compounds but they checked the biological properties of the crude methanolic extract of Lobophytum crassum from the coast of Madagascar [24]. In other work, Al-Footy et al. [53] reported that among diverse secondary metabolites isolated from the soft coral Lobophytum sp. collected off the Red Sea Coast, in Jeddah, Saudi Arabia, only the known cembrane diterpenoid (cembrene A) had an antibacterial activity against several Gram-positive and Gram-negative There are also the polycyclic norcembranoid diterpenes, rare and found exclusively in soft corals of the genus Sinularia. These diterpenes are within the family of furanecembranoids which lack a C-18 carbon substituent in comparison with C20-cembranoids. They co-occur with 14-membered macrocyclic norcembranoids with a furan heterocycle in which also lacks a C-18 carbon substituent [19]. The mechanisms leading to the occurrence of norcembranoid diterpenes are not well understood but they may include the production of anionic and radical intermediates along with competitive transannular carbon-to-carbon bond-forming reactions. However, these are only proposals that, according to the authors [19], must be validated in forthcoming biosynthetic studies.
The extraction of cembranoid diterpenes was generally made with organic solvents (acetone, chloroform, ethanol, ethyl acetate, methanol, and methylene chloride) by maceration (Tables 2-4), followed by the concentration under vacuum. Afterwards, the residue is partitioned between pairs of solvents and further column chromatography eluting with a gradient of solvents with increasing polarity. Different fractions originate the cembranoid compounds, which can be subjected to semior preparative HPLC (high performance liquid chromatography). The identification of compounds is generally made through 1 H-NMR (proton nuclear magnetic resonance), 13 C-NMR (Carbon-13 nuclear magnetic resonance), one dimensional and two dimensional nuclear magnetic resonance (1D-NMR and 2D-NMR) including 1 H-1 H COSY, HMQC, HMBC, and NOESY spectra (Correlation Spectroscopy, Heteronuclear Multiple-Quantum Correlation, Heteronuclear Multiple-Bond Correlation Spectroscopy, Nuclear Overhauser Effect Spectroscopy, respectively), Time-Dependent Density Functional Theory Electronic Circular Dichroism (TDDFT/ECD), Density Functional Theory (DFT)/NMR calculations, FTIR (Fourier-transform infrared spectrosocopy), single crystal X-ray diffraction, and LC-MS-IT-TOF (liquid chromatography-mass spectrometry-ion trap-time-of-flight) [9,.
The review upon the source, chemistry and bioactivities of new cembrane diterpenes from marine organisms, since 2016 (27 works) (Tables 2-4) revealed that the most important sources of cembrane derivatives found in that period were coming from the genus Sarcophyton (14 works), Sinalarina (8 works) and Lobophytum (5 works). There is still one work in which the authors did not isolate new cembrane compounds but they checked the biological properties of the crude methanolic extract of Lobophytum crassum from the coast of Madagascar [24]. In other work, Al-Footy et al. [53] reported that among diverse secondary metabolites isolated from the soft coral Lobophytum sp. collected off the Red Sea Coast, in Jeddah, Saudi Arabia, only the known cembrane diterpenoid (cembrene A) had an antibacterial activity against several Gram-positive and Gram-negative

Other cembranes
Planaxool (14) Marine mollusk Planair sulratru There are also the polycyclic norcembranoid diterpenes, rare and found exclusively in soft corals of the genus Sinularia. These diterpenes are within the family of furanecembranoids which lack a C-18 carbon substituent in comparison with C20-cembranoids. They co-occur with 14-membered macrocyclic norcembranoids with a furan heterocycle in which also lacks a C-18 carbon substituent [19]. The mechanisms leading to the occurrence of norcembranoid diterpenes are not well understood but they may include the production of anionic and radical intermediates along with competitive transannular carbon-to-carbon bond-forming reactions. However, these are only proposals that, according to the authors [19], must be validated in forthcoming biosynthetic studies.
The extraction of cembranoid diterpenes was generally made with organic solvents (acetone, chloroform, ethanol, ethyl acetate, methanol, and methylene chloride) by maceration (Tables 2-4), followed by the concentration under vacuum. Afterwards, the residue is partitioned between pairs of solvents and further column chromatography eluting with a gradient of solvents with increasing polarity. Different fractions originate the cembranoid compounds, which can be subjected to semior preparative HPLC (high performance liquid chromatography). The identification of compounds is generally made through 1 H-NMR (proton nuclear magnetic resonance), 13 C-NMR (Carbon-13 nuclear magnetic resonance), one dimensional and two dimensional nuclear magnetic resonance (1D-NMR and 2D-NMR) including 1 H-1 H COSY, HMQC, HMBC, and NOESY spectra (Correlation Spectroscopy, Heteronuclear Multiple-Quantum Correlation, Heteronuclear Multiple-Bond Correlation Spectroscopy, Nuclear Overhauser Effect Spectroscopy, respectively), Time-Dependent Density Functional Theory Electronic Circular Dichroism (TDDFT/ECD), Density Functional Theory (DFT)/NMR calculations, FTIR (Fourier-transform infrared spectrosocopy), single crystal X-ray diffraction, and LC-MS-IT-TOF (liquid chromatography-mass spectrometry-ion trap-time-of-flight) [9,.
The review upon the source, chemistry and bioactivities of new cembrane diterpenes from marine organisms, since 2016 (27 works) (Tables 2-4) revealed that the most important sources of cembrane derivatives found in that period were coming from the genus Sarcophyton (14 works), Sinalarina (8 works) and Lobophytum (5 works). There is still one work in which the authors did not isolate new cembrane compounds but they checked the biological properties of the crude methanolic extract of Lobophytum crassum from the coast of Madagascar [24]. In other work, Al-Footy et al. [53] reported that among diverse secondary metabolites isolated from the soft coral Lobophytum sp. collected off the Red Sea Coast, in Jeddah, Saudi Arabia, only the known cembrane diterpenoid (cembrene A) had an antibacterial activity against several Gram-positive and Gram-negative There are also the polycyclic norcembranoid diterpenes, rare and found exclusively in soft corals of the genus Sinularia. These diterpenes are within the family of furanecembranoids which lack a C-18 carbon substituent in comparison with C20-cembranoids. They co-occur with 14-membered macrocyclic norcembranoids with a furan heterocycle in which also lacks a C-18 carbon substituent [19]. The mechanisms leading to the occurrence of norcembranoid diterpenes are not well understood but they may include the production of anionic and radical intermediates along with competitive transannular carbon-to-carbon bond-forming reactions. However, these are only proposals that, according to the authors [19], must be validated in forthcoming biosynthetic studies.
The extraction of cembranoid diterpenes was generally made with organic solvents (acetone, chloroform, ethanol, ethyl acetate, methanol, and methylene chloride) by maceration (Tables 2-4), followed by the concentration under vacuum. Afterwards, the residue is partitioned between pairs of solvents and further column chromatography eluting with a gradient of solvents with increasing polarity. Different fractions originate the cembranoid compounds, which can be subjected to semi-or preparative HPLC (high performance liquid chromatography). The identification of compounds is generally made through 1 H-NMR (proton nuclear magnetic resonance), 13 C-NMR (Carbon-13 nuclear magnetic resonance), one dimensional and two dimensional nuclear magnetic resonance (1D-NMR and 2D-NMR) including 1 H-1 H COSY, HMQC, HMBC, and NOESY spectra (Correlation Spectroscopy, Heteronuclear Multiple-Quantum Correlation, Heteronuclear Multiple-Bond Correlation Spectroscopy, Nuclear Overhauser Effect Spectroscopy, respectively), Time-Dependent Density Functional Theory Electronic Circular Dichroism (TDDFT/ECD), Density Functional Theory (DFT)/NMR calculations, FTIR (Fourier-transform infrared spectrosocopy), single crystal X-ray diffraction, and LC-MS-IT-TOF (liquid chromatography-mass spectrometry-ion trap-time-of-flight) [9,.
The review upon the source, chemistry and bioactivities of new cembrane diterpenes from marine organisms, since 2016 (27 works) (Tables 2-4) revealed that the most important sources of cembrane derivatives found in that period were coming from the genus Sarcophyton (14 works), Sinalarina (8 works) and Lobophytum (5 works). There is still one work in which the authors did not isolate new cembrane compounds but they checked the biological properties of the crude methanolic extract of Lobophytum crassum from the coast of Madagascar [24]. In other work, Al-Footy et al. [52] reported that among diverse secondary metabolites isolated from the soft coral Lobophytum sp. collected off the Red Sea Coast, in Jeddah, Saudi Arabia, only the known cembrane diterpenoid (cembrene A) had an antibacterial activity against several Gram-positive and Gram-negative microorganisms. For this reason, the brief review aims at identifying the new compounds found in those species belonging to these genera, during that period.
Fourteen works regarding new cembranoid diterpenes from the genus Sarcophyton (S. cherbonnieri, S. ehrenbergi, S. elegans, S. stellatum, S. subviride, and S. trocheliophorum) were found during the last three years. These species of soft corals were collected at several places: seven samples in the South China Sea (one Sarcophyton sp., one S. ehrenbergi, one S. elegans, one S. stellatum, one S. subviride and two S. trocheliophorum); two samples of Sarcophyton sp. in the Celebes Sea; one sample of S. stellatum in the Indian Ocean; one sample of S. cherbonnieri in the Philippine Sea; and three samples collected in the Red Sea Coast (one S. ehrenbergi and two S. trocheliophorum) ( Table 2).
There is a work in which the isolation and identification of metabolites were not performed. Only the antimicrobial and cytotoxicity activities of extracts of two soft corals (Lobophytum microlobulatum, Sarcophyton auritum), three seaweeds (Caulerpa racemosa, Caulerpa sertularioides, Kappaphycus alvarezii), and a marine sponge (Spheciospongia vagabunda) collected from Malaysian coast were determined. Hexane extract of Sarcophyton auritum exhibited strong fungicidal activity against dimorphic yeast Cryptococcus neoformans, with minimal inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) values of 0.04 mg/mL (in both). The ethyl acetate extract of S. auritum showed strong inhibition on the cytopathic effect induced by the Chikungunya virus (a re-emerging mosquito-borne virus) with 50% effective concentrations of 176.6 +/− 9.7 mu g/mL. According to Chan et al. [59], extracts from the two soft corals (L. microlobulatum and S. auritum) possessed stronger antimicrobial activity than the seaweeds and the sponge.
Beyond the publications regarding the discovery of new cembrane diterpenoids in the genus Sarcophyton as well as their biological properties, three other publications with distinct approaches were found. One of them aimed at examining the effect of oxylipin analogues [prostaglandin E1 (PG-E1), methyl jasmonate, and arachidonic acid in addition to the geranylgeranylpyrophosphate] and wounding on the secondary metabolism of the soft corals Sarcophyton glaucum and Lobophyton pauciflorum [60]. According to the authors, the PG-E1 was more effective for upregulating campestene-triol and a cembranoid than methyl jasmonate in the soft corals Sarcophyton glaucum. In addition, the effect of the elicitors in Lobophyton pauciflorum was poorer than that in Sarcophyton glaucum [60]. The second one applied the quantitative NMR (qNMR) for assessing the diterpene variation in 16 soft coral specimens in the context of their genotype, origin, and growing habitat. The study revealed higher diterpene amounts in Sarcophyton sp. than in Sinularia or Lobophyton [29]. In their publication, Farag et al. [29] reported the metabolite profile of the soft coral genus Sarcophyton in different habitats along the coastal Egyptian Red Sea, was performed through 1 H-NMR and ultra-performance liquid chromatography-mass spectrometry (UPLC-MS). At the same time, the authors compared the metabolite profile of these wild soft corals with those growing in aquarium. Generally, wild soft corals presented more bioactive compounds than aquarium grown ones. This discrepancy found between wild and aquarium grown corals were attributed, by the authors, to the lack of necessity for producing compounds acting as defenses against predators absent in tanks.
The large-scale metabolomics analyses were made for the first time in 16 Sarcophyton species, comparing MS (mass spectra) and NMR results. The metabolomic fingerprinting and profiling of those soft coral extracts were made through 1D and 2D-NMR without any preliminary chromatographic assay. In parallel to the chromatographic mass spectrometry techniques, permitted to identify 120 metabolites including 65 diterpenes, 8  projection to latent structures-discriminant analysis (OPLS-DA) for samples classification [30]. In the same work, they concluded that UPLC-MS (ultra-performance liquid chromatography-mass spectrometry) revealed to be better tool for a compound based classification of coral species than NMR technique. However, NMR or UPLC−MS data sets were likewise effective in foreseeing the species origin of unknown Sarcophyton after applying PCA [30].
The biological properties, particularly antiplasmodial activity against the FCM29 strains of Plasmodium falciparum and antimicrobial was only studied with some extracts of the sponge Pseudoceratina arabica. Only the methanolic extract of S. stellatum, was biologically evaluated against P. falciparum. It presented only a moderate inhibition activity (IC 50 = 35.20 µg/mL) [24]. Two new biscembranoid-like compounds were obtained from the soft coral Sarcophyton subviride from the coast of Xisha, Hainan Province (China) [26]. They were bissubvilides A (72) and B (73) (Figure 8), that resulted from a Diels-Alder cycloaddition of two cembrane monomers. These compounds did not present any cytotoxic activity against human osteosarcoma MG-63 (IC50 > 30 μM) or A549 lung cancer (IC50 > 25 μM) cells or Huh7 human hepatology cancer stem cells (IC50 > 50 μM). Sarsolilide (60) was also detected in the soft coral Sarcophyton subviride from the coast of Xisha [26]. Two new biscembranoid-like compounds were obtained from the soft coral Sarcophyton subviride from the coast of Xisha, Hainan Province (China) [26]. They were bissubvilides A (72) and B (73) (Figure 8), that resulted from a Diels-Alder cycloaddition of two cembrane monomers. These compounds did not present any cytotoxic activity against human osteosarcoma MG-63 (IC 50 > 30 µM) or A549 lung cancer (IC 50 > 25 µM) cells or Huh7 human hepatology cancer stem cells (IC 50 > 50 µM). Sarsolilide (60) was also detected in the soft coral Sarcophyton subviride from the coast of Xisha [26]. Two new biscembranoid-like compounds were obtained from the soft coral Sarcophyton subviride from the coast of Xisha, Hainan Province (China) [26]. They were bissubvilides A (72) and B (73) (Figure 8), that resulted from a Diels-Alder cycloaddition of two cembrane monomers. These compounds did not present any cytotoxic activity against human osteosarcoma MG-63 (IC50 > 30 μM) or A549 lung cancer (IC50 > 25 μM) cells or Huh7 human hepatology cancer stem cells (IC50 > 50 μM). Sarsolilide (60) was also detected in the soft coral Sarcophyton subviride from the coast of Xisha [26].  Figure 9) isolated from the Red Sea soft coral Sarcophyton trocheliophorum was evaluated by Zubair et al. [28]. Along with this new compounds, the known diterpene cembrene C (77) was also isolated and identified from the same natural source. Trocheliane (76) was active against the two multidrug-resistant bacteria Acinobacter baumannii and Staphylococcus aureus. The MIC of this compound ranged from 4 to 6 µM for all the tested bacteria (A. baumannii, S. aureus, S. epidermidis, Streptococcus pneumoniae, Escherichia coli, Klebsiella pneumonia, and Pseudomonas aeruginosa) [28].
Nine new cembranoids, sarcophytrols M-U (82-90) (Figure 9), were isolated from the South China Sea soft coral S. trocheliophorum, along with one already known. Such new compounds possess diverse types of cyclized rings: furan rings in sarcophytrols M-P (82-85), pyran rings in sarcophytrols, oxepane, and peroxyl rings in sarcophytrols T (89) and U (90), respectively. Sarcophytrols R (87) and S (88) had a rare bicyclic skeleton of the decaryiol-type, as reported for the first time for the same genus of soft coral S. decaryi [23]. The bioassay for evaluating the capacity for inhibiting human protein tyrosinase phosphatase 1B (PTP1B) enzyme, important for the treatment of type-2 diabetes and obesity, all compounds isolated from the soft coral S. trocheliophorum did not provide positive results. Cytotoxicity against the human tumor cell lines HL-60 (Human promyelocytic leukemia cells) and K-562 (human erythroleukemia cells), as well as the antibacterial activity of the same compounds against P. aeruginosa also revealed negative [23]. Later on, the authors isolated and  [34]. Sartrolide H (94) and 4Z,12Z,14E-sarcophytolide (98) had moderate inhibitory activity against protein tyrosine phosphatase 1B (key target for the treatment of type-II diabetes and obesity) with IC 50 = 19.9 and 15.4 µM, respectively, significantly less than the positive control, oleanolic acid (IC 50 = 2.6 µM). 4Z,12Z,14E-Sarcophytolide (98) had also moderate inhibitory activity against Staphylococcus aureus Newman strain (MIC 50 = 250 µM), less than the positive control, fosfomycin (MIC 50 = 137.4 µM) [34].

Isopropyl cembrane
It did not exhibit cytotoxic activity against human promyelocytic leukemia cells (HL-60) (IC 50 > 30 µg/mL) It was not able to prevent the accumulation of NO, PGE 2 and pro-inflammatory cytokines (TNF-α, IL-1β and IL-6) in LPS-induced RAW 264.7 cells, that is, it did not possess anti-inflammatory activity It had strong activity against the seaweed pathogens Alteromonas sp., Cytophaga-Flavobacterium and Vibrio sp.

New Cembrane Derivatives from the Genus Sinularia
Soft coral Sinularia consists of more than 150 species [36]. As aforementioned for Sarcophyton sp., reviews have also been made regarding the discovery of new compounds and their biological activities up to 2016 [11][12][13][14]17]. During the period 2016-2017, only three publications could be found in the Web of Science utilizing the words cembrane, cembranoid, and Sinularia (one study in 2016 [37] and two studies in 2017 [38,39]), whereas in the first half of 2018 seven publications could be found using the same database [40][41][42][43][44][45][46]. The species reported in eight works included one S. erecta, one S. compacta, two Sinularia sp., and four S. flexilibis, all of them from the South China Sea (Table 3). In addition, there are other works in which one of them was focused on the biological activity of sinularin extracted from marine soft corals (S. flexibilis and S. manaarensis) [40] and the other one identified five cembranoid diterpenes (isosinulaflexiolide K, sinulaflexiolide K, sandensolide, sinularin, and dendronpholide F) obtained from cultured soft coral S. flexibilis [41] but without any biological activity determination. The anti-breast cancer activity (SKBR3 and MDA-MB-231 cells) of sinularin extracted from marine soft corals (S. flexibilis and S. manaarensis) were detected by [40], nevertheless, it was almost non-toxic against breast normal (M10) cells, at least after 24 h treatment. On the SKBR3 cells, the mechanisms involved on the anticancer activity included the induction of the G2/M cycle arrest, apoptosis of cells, and oxidative stress and DNA damage, as well as the pancaspase activity, and activation of poly(ADP-ribose) polymerase (PARP), and caspases 3, 8, and 9 [40].
Cytotoxicity activity of cembranoids isolated from the Taiwanese soft coral S. flexibilis was evaluated by Wu et al. [45]. According to the authors five new cembranoid-related diterpenes [flexibilisins D (146) and E (147), secoflexibilisolides A (148) and B (149), and flexibilisolide H (150)] ( Figure 14) were isolated from this soft coral along with nine known compounds. The known 11-dehydrosinulariolide (144) possessed selective cytotoxicity towards P388 (murine leukemia) cell line, and (145) presented remarkable cytotoxicity activity and selectivity on P-388 and HT-29 (human colon carcinoma) cell lines [45]. The new compounds, however, did not exhibit any activity towards these two types of cells since they presented IC 50 values over than 40 µM. The anti-inflammatory activity was also determined but only (142) had capacity for inhibiting superoxide anion formation and elastase release in N-formyl-methionyl-leucyl-phenylalanine/cytochalasin B (fMLF/CB)-induced human neutrophils at a concentration of 10 µM [45]. The anti-inflammatory activity of the cembranoids isolated from the S. flexibilis collected off the coast of Yalong bay, Sanya in Hainan province (China) was also evaluated by Zhao et al. [46] through the capacity for inhibiting the LPS-induced NO and TNF-α generation in the RAW264.7 macrophage cells. Sinularin (143) was the best among the compounds isolated by the authors, displaying inhibition percentages higher than 80%, at 10 µM, significantly higher when compared to the new cembranoid diterpenes [sinulaflexiolides L-O (151-154) and ent-sinuflexibilin D (141)] identified by the authors [46].  (Figure 14). Epoxycembrane A (155) was for the first time reported in S. flexibilis [39]. Tributyltin and copper are antifouling largely used in order to deter marine fouling organisms on the surfaces of artificial structures submerged in the sea, but they present some drawbacks particularly due to their adverse environmental impacts [39]. For this reason, several attempts have been made for finding more environmental friendly compounds. Wang et al. [39] assayed the antifouling activity on the larvae of the bryozoan Bugula neritina and the barnacle Balanus albicostatus of all the cembranoid diterpenes isolated from S. flexibilis. With the exception of (143), all remaining ones presented activity, and particularly (142) had the highest antifouling activity against both Bugula neritina and barnacle Balanus albicostatus [the concentrations of the compound that inhibited settlement by 50% relative to the control (EC 50 ) were 3.90 µg/mL and 21.26 µg/mL, respectively], and low toxicity against B. albicostatus larvae [the concentration that originates 50% mortality) (LC 50 ) > 100 µg/mL]. According to the authors [39], the antifouling activity of (142), (144), (155), (157), and (158) was reported for the first time.
During 2016-2018, the most studied of soft coral species was L. crassum, either in terms of biological properties of known cembranoids or research of new cembranoid diterpenes. This species was collected in several places (Table 4). Species L. crassum is well known to produce oxygenated cembranoids. The structural variety of these metabolites is often correlated with geographic variation and environmental conditions [54]. The soft coral L. crassum from the South China Sea was studied by [54] and from this study, the authors isolated and  Table 4). The remaining metabolites did not present inhibitory effect (IC 50 > 30 µM) [54].    (Figure 15) [9]. The anti-inflammatory activity of the cembranoid compounds was evaluated studying the effect of these compounds on the LPS-induced interleukin 12 (IL-12) release and NO production in dendritic cells [9]. The results showed that (174), (176) and sinulariol D (127) (<50 µg/mL) presented a potent inhibitory effect of IL-12 and NO release (86.1-96.2%). Moreover, the same compounds also had considerable cytotoxicity (Table 4) [9].
Mohamed et al. [56] isolated from L. crassum, collected off the coast of Dongsha Atoll (South China Sea), three new cembranoids [lobophylins F-H (180-182)], together with three known ones lobophylin C (183-185) ( Figure 15). Rahelivao et al. [24] did not isolate cembranoids from the soft coral L. crassum extract from the coast of Madagascar, but only they reported the moderate activity of the crude methanol extract against the malarial parasite FCM29 strain of Plasmodium falciparum (IC 50 value of 33.15 µg/mL). In other work, Lin et al. [55] studied the anticancer ability of lobocrassin B (186) (Figure 15), a natural cembrane diterpenoid previously isolated from the soft coral L. crassum. The authors reported that this compound exerted cytotoxic effects for concentrations <10 µM on lung cancer CL-15 and H520 cells lines, not only by decreasing cell viability but also by inducing apoptosis, oxidative stress and mitochondrial dysfunction (increased level of Bax, cleaved caspase-3, -9 and

Concluding Remarks
The use of increasingly sophisticated equipment has permitted to identify new compounds, including natural compounds of marine origin. The aim is to find remarkable biological properties for possible application in Medicine. A huge diversity of chemical structures have been isolated and evaluated in biological terms from marine organisms. The soft corals belonging to the family Alcyoniidae are not an exception. They are, indeed, the target of several studies in searching for new products with biological properties, particularly antimicrobial, anti-inflammatory, and anti-tumoral activities. Cembranoids from soft corals of the genera Sinularia, Lobophytum, and Sarcophyton are the most well studied secondary metabolites of the specimens belonging to these genera. The chemical diversity of cembranoid diterpenes is remarkable and evident from previous studies. Such diversity can be attributed to the differences in environmental conditions between the different localities, like: surface temperature, salinity, nutrient concentrations, and turbidity. However, in the present review it is important to emphasize the following points: in Sarcophyton species the new compounds isolated by the authors belonged predominantly and by descending order to: isopropyl cembranes, 5-membered lactones, biscembranoids, and furanocembranoids; in Sinularia species, the new cembrane compounds were predominantly lactones (5 or 6-membered ones) and isoprenyl cembranes; in the Lobophytum species there was no predominance of any type of cembrane diterpenoids. In this case, isopropyl, isopropenyl, isoprenyl acid, 5-and 7-membered lactones, furanocembranoid or even casbane types were detected without any predominant one.
The diversity of results in what concerns the biological properties reported in several works can be partly attributed to the variability of chemical structures found, even though the presence of some chemical groups or their arrangement in the cembranoid diterpene core can be determinant in such activities. In the present review, citotoxicity was evaluated in seven works using diverse tumor cell lines (lung, liver, colon, osteosarcoma, ovarian, breast, leukemia) the species of the genus Sarcophyton. However, moderate activity was detected in only two researches; mainly against liver, lung (S. ehrenbergi from the Red Sea Coast) and breast (Sarcophyton sp. from Celebes Sea). The antibacterial activity was the second most important activity scrutinized by the researchers, but the activity was only moderate to weak or even absent for the microorganisms used. For example, for Staphylicoccus aureus, the activity found ranged for inactive (pyrane-based cembranoid diterpene) to active against multidrug resistant strain (the biscembrane hydrocarbon trocheliane). Anti-inflammatory activity was positive in all assays independent on the methodology used: inhibition of production of NO, interleukins, prostaglandins, TNF-α by LPS-LPS-stimulated macrophage cells; inhibition of expression of COX-2 or inhibition of superoxide anions generation. In contrast, in Sinularia species, there is a species (S. flexibilis) in which no anti-inflammatory or antioxidant activity was found, whereas in other cases S. flexibilis presented an anti-inflammatory activity. The citotoxicity towards several tumor cell lines were detected either in species of the genus Sinularia or Lobophytum, but with diverse strengths.
Although such diversity of results can be attributed to the chemical groups and their arrangement in the core structure, it would be advisable to find other approaches to identify biological properties. Sometimes it is unclear the reasons that led the researchers to determine certain activities as well as the choice of some cells or parameters. Whether for plant kingdom, the ethnobotany or ethnopharmacology are strong tools for searching bioactive compounds, in the marine world cannot provide enough information, whereby other approaches must be taken into account. World data libraries compiling the results obtained so far, along with structure-based drug design methods (e.g., molecular docking, structure-based virtual screening and molecular dynamics) can predict in some extent possible activities and interactions with diverse targets, maybe more adequate and less expensive than the current way generally followed. The resistance of microorganisms to antibiotics is of great concern, therefore the bactericidal activity found for 16-hydroxycembra-1,3,7,11-tetraene, or the activity against the two multidrug resistant bacteria Acinobacter baumannii and Staphylococcus aureus of trocheliane should be deeply studied not only in the search of new compounds with similar structures or, even better, those molecules can serve as templates for the construction of new molecules after adequate modifications.