## 2 Classes of Secondary Metabolites
### Biscembranes  
Four biscembranes, bisglaucumlides A-D **325-328** were isolated from _S. glaucum_. Spectral data showed that bisglaucumlide A **325** possessed a biscembranoid skeleton. Bisglaucumlide B **326** was confirmed to be 32-acetylbisglaucumlide A by the positive Cotton effect in the CD spectrum. As for bisglaucumlide C **327** it was found to be the geometrical isomer of bisglaucumlide B **326** while considering the geometry of the C-4 olefin. Bisglaucumlide D **328** was an isomer to bisglaucumlide C **327**, its absolute configuration indicated an anticlockwise relation among the enone chromopores revealing a negative Cotton effect CD spectrum [102]. Moreover, chemical investigation of _S. glaucum_ extract yielded two biscembranes with an uncommon \(\alpha\), \(\beta\)-unsaturated \(\varepsilon\)-lactone, Glaucumolides A and B **329-330**[103].  
Ximaolides A-G **331-337**, seven biscembranoid, together with methyl tortuosoate A **338** where isolated from _S. tortuosum_. Their structures were elucidated through spectral analysis and Ximaolide A **331** and E **335** relative stereochemistry were investigated using X-ray diffraction method. The authors demonstrated that methyl tortuosoate A **338** could be the biogenetic precursor for all isolated metabolites since their upper parts were closely related to compound **338**[104].  
Figure 4: Diterpenes reported from _Sarcophyton_ sp.  
A cembranolide diterpene identified as isosarcophytonolide D **339**, an isomer to the previously isolated compound **41** from _S. tortuosum_, along with two biscembranes, bislatumlides A and B **340-341**, were isolated from _S. latum_. A detailed spectral analysis revealed that the structure of bislatumlide B **341** matched that of bislatumlide A **340**. However, \({}^{13}\)C NMR data revealed a significant difference from compound **340** in the chemical shifts of carbon-19 and carbon-10 demonstrating the Z nature of \(\Delta^{11}\) olefin in compound **340**. Thus, compound **340** was found to be the 11Z isomer of bislatumlide B **341**. Interestingly the authors have proposed a biosynthetic pathway for bislatumlides A and B **340-341** in which isosarcophytonolide D **339** was found to be one of the precursors for bislatumlide A **340**. Moreover, the authors investigated the effect of long-term storage in CDCl\({}_{3}\), where it showed isomerization of bislatumlide A **340** to bislatumlide B **341** at \(\Delta^{11}\)[105].  
Methyl tetrahydrorosarcoma and methyl tetrahydroiossoarcoate **342** and **343**, two cembranoids isolated from _S. elegans_, along with four biscembranoids, nyalolide, desacetylnyalolide, diepoxynyalolide, and dioxanyalolide **344-347**. The authors proposed that diepoxynyalolide **346** could be a precursor for both compound nyalolide **344** and dioxanyalolide **347**[106].  
Investigation on _S. elegans_ extract led to the isolation of six biscembranoids identified as sarcophytolides G-L **348-353**, together with biscembranoids, lobophytones H, Q, K, W, U **354-358**. Isolates structure were determined by spectroscopic analysis. Absolute configuration of the compound sarcophytolide G **348** was determined using Mosher reaction [22; 107]. From the methanol extract of _S. paucplicatum_, sarcophytolides M and N **359** and **360**, along with lobophytone O **361**, were isolated [108].  
Two biscembranoids, sarelengans A and B **362** and **363**, were reported from _S. elegans_. Their chemical structures were investigated by spectral and chemical methods, and the absolute configuration of sarelengans A determined by single crystal X-ray diffraction. Sarelengans A and B **362** and **363** possessed a conjuncted trans-fused A/B-ring between two cembranoid entities. The authors mentioned that this structure feature led to an uncommon biosynthetic pathway including a cembranoid-\(\Delta^{8}\) instead of cembranoid-\(\Delta^{1}\) unit in endo-Diels-Alder cycloaddition [94]. Figure 5 summarizes biscembranes isolated from _Sacrophyton_ sp.