Terpenoid Constituents from Porifera

F (122) was found to be identical with ageline A (122) previously reported by Capon and Faulkner (92). Nakatsu et al (106) determined the structure of an unusual purine-containing diterpene (129), an artifact derived from an unstable base that was the major antimicrobial metabolite of Agelas mauritiana. 

Manes et al. (110) isolated two substances from an undescribed Prianos species. While the major compound was a or-sesterterpene which will be discussed in the next section together with other sesterter-penes, the minor one was a or-diterpene peroxide, methyl nuapapuan-oate (142). Capon and Macleod (110a) obtained another r-diterpene peroxide (143) from an unidentified sponge. 

Many species of the sponge genus Spongia contain biosynthetically intriguing C21 difuranoterpenes probably derived from linear sesterter-pene tetronic acids such as variabilin (146) which has long been known as a constitutent of Ircinia variabilis, A detailed discussion of sesterter- 

Luffariella variabilis provided four sesterterpenoid antibiotics (159-162) (117, 118). Manoalide (159) which contains an a,P-unsatu-rated 5-lactol function was without close structural analogy. 160 was an open chain isomer of 159, with -configuration of the C-6,7 double bond which prevents ring closure between the C-24 aldehyde and the 

A unique tetracyclic furanosesterterpene, wistarin (195), has been discovered in Ircinia wistarii in addition to the previously known isomer ircinianin (196) 131). 196 decomposed readily, whereas 195 was relatively stable. As wistarin (195) was not detected among the decomposition products of 196 and 196 did not undergo cyclization to 195 on treatment with dilute acid, base or Lewis acids, it was proposed that 195 was a natural product and not an artifact. The biosynthesis of these sesterterpenes must involve a different folding of the acyclic 25-precursor. 

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Several terpenoid furans have been isolated from Cadlina luteomar-ginata, most of them cited previously as metabolites from Porifera. Two more compounds from this species were dendrolasin (791) and pleraplysillin-1 (792) (524). Dendrolasin (791) was also a constituent of Hypselodoris ghiselini and H. califomiensis (78). The digestive glands of Dendrodoris grandiflora contained the previously known sesquiterpenes microcionin-1 (793), -2 (777), -3 (794), and -4 (795) (528). 

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