Acanthella pulcherrima

The structures and relative stereochemistry of epi-eudesmanes 25-27 from Axinella cannabina were formulated from 2D NMR and chemical correlation experiments [36]. The 500 MHz HNMR spectrum of 1 l-formamido-7/ H-eudesm-5-ene (27) measured in CDC13 showed a 2 3 cis.trans ratio of the -NHCHO group (cis 3 8.06 d, J = 2 Hz trans 5 8.20 d, J — 12 Hz). Isothiocyanate 26 was one of several sesquiterpenes reported from Acanthella pulcherrima [20]. 

Amorphanes 38-40 were also isolated from Acanthella cannabina. These are trans-fused and functionalized at C-l rather than C-10 which was the case with the Halichondria metabolites. The carbocyclic skeleton was demonstrated when 39 was dehydrogenated to yield cadalene (37). Relative stereochemistry assignments were secured by extensive 13C- and XH NMR experiments [39], in which 13C data were particularly useful, as illustrated in the case of isothiocyanate 41, one of several isothiocyanates obtained from Acanthella pulcherrima [20]. The ds-fused ring was corroborated by comparing the corresponding chemical shifts with those of enf-epicubenol (42) [20], which has the same relative stereochemistry. 

Along with epi-eudesmanes, 25-27, alloaromadendranes 58-60 were separated from the chloroform solubles of a methanol extract of A. cannabina [36], As was the case with axisonitrile-2 (53), extensive spectroscopic analyses including Eu(fod)3 shift reagent experiments in XH- and 13C NMR permitted assignment of relative stereochemistry. Acanthella pulcherrima was also a source of isothiocyanate 59, although both isonitrile and formamido compounds appear to be absent [20],... 

Biological specificity is a paramount consideration if one considers two examples, Acanthella pulcherrima [20] and Pseudaxinyssa sp. [68], That thiocyanate ion may be the precursor to marine isothiocyanates should be tested on these organisms since isothiocyantes were the primary representative of the triad. Also, should incorporation of thiocyanate ion by Phycopsis terpnis yield 81 and 82 [48], rather than the unreported corresponding isothiocyanates, the biospecificity of marine organisms will be demonstrated. 

A species of Halichondria from the Marshall Islands contained an isothiocyanate (249) [255] and an isothiocyanate based on the guai-6-ene skeleton (250) was isolated from an unidentified sponge from Japanese waters [256]. Acanthella pulcherrima from Australia contained two isothiocyanates (251-252), in addition to known sesquiterpenes [257]. 

Kalihinols G (277) and H (278) were trace components of a species of Acanthella from Guam and kalihinol X (279) was isolated from a Fijian species of Acanthella. All inhibited growth of Bacillus subtilis, Staphylococcus aureus and Candida albicans [278]. 10-Epi-isokalihinol H (280) and 15-isothiocyanato-l-epi-kalihinene (281) were isolated from Acanthella cavernosa from the Seychelles [279]. A Japanese specimen of A. cavernosa contained a sesquiterpene isothiocyanate (282) and 10 3-formamido-5p-isothiocyanatokalihinol A (283). Structures were assigned by spectral data interpretation [280]. Phakellia pulcherrima from the Philippines contained the minor diterpene isothiocyanates kalihinol L (284), 10-isothiocyanatokalihinol G (285), 10-epi-kalihinol H (286) and 10-isothiocyanatokalihinol C (287) [281]. 10-Epi-kalihinol I (288) and 5,10-bisisothiocyanatokalihinol G (289) were isolated from an Acanthella sp. from Okinawa [282]. 

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