KalihinolE

We have used the Kupchan scheme successfully in the separation of the multifunctional diterpenoid kalihinols from various Acanthella species (cf. Sect. 4.2.2). These compounds were distributed between the carbon tetrachloride and chloroform layers [19, 25], No isocyanosesquiterpenes were present in the hexane layer. By contrast, separate experiments with the Australian A. klethra revealed that sesquiterpenoid isonitriles were found exclusively in the hexane extract. No kalihinols were present in the carbon tetrachloride or chloroform extracts [26],... 

During our studies of the kalihinols (Sect. 4.2.2), isothiocyanate 28 was one of several isocyano-related compounds isolated from Acanthella klethra from Australia. Its structure was also published independently from a Ciocalypta sp. in Hawaii [37] and reported as a poster at the 1988 Gordon Research Confer-... 

To separate homogeneous compounds from co-eluting metabolites, repeated HPLC experiments with changes in column and solvent systems were necessary. For example, kalihinol-A (107) sharing similar retention times with kalihinol-C (114), and kalihinol-F (112) with kalihinol-E (108), were resolved successfully on an ODS reverse phase column. Crystallization experiments were repeatedly undertaken. The sample of kalihinol-F (112) prepared for X-ray analysis had two C22H33N3O2 molecules in its asymmetric unit. 

Independent studies involving two separate collections of A. cavernosa from Fiji afforded kalihinol-A (107), -F (112), -X (109), and a new compound, isokalihinol F (118) [65]. The latter was obtained from a batch, in which kalihinol-A was the major component. Recollection of the same sponge a year later, however, resulted in -X (109), -Y (110), and -Z (111) as the only kalihinols [65], It is unclear, whether seasonal variation is the determining factor of the chemical changes noted in A. cavernosa. Our sample from Fiji identified only at the genus level contained kalihinol-X, -Y, -Z, and minor kalihinols, none of which were found identical (TLC examination) to the A-H types of the Guam Acanthella [19]. 

A subsequent study of A. cavernosa from Thailand by California workers revealed two additional F-type kalihinols in addition to kalihinol-X (109) and -Y (110) [45]. The structures of kalihinol-I (121) and -J (122) were secured by low resolution chemical ionization mass spectral and NMR data. Both 1H-1H COSY and 13C NMR techniques were used extensively. Furthermore, hydrolysis of compound 109 to kalihinol-J (122) confirmed the assignments. 

Use of encapsulated labeled precursors in lipid vesicles enabled the Hawaiian group to conduct the biosynthetic studies - with the exception of workup of the sponge - entirely in the field. Incorporation of doubly labeled [13C, 15N]cyanide into a Ciocalypta sp. and an Acanthella sp. produced labeled 9-isocyanoneopupukeanane (77) and kalihinol-F (112) respectively [71]. Detection of incorporation was followed by 13C NMR experiments. 

Additional reports of multifunctional kalihinols implicate a polar and stepwise biosynthetic cationic mechanism [21, 45]. 

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]. 

Diterpene isothiocyanates fall into three distinct structural categories regarding their carbon skeletons the acyclic tetraenes (220 and 221), the biflorane framework (including the kalihinol family) (222-238), and the amphilectane framework (including the cyclo- and isocycloamphilectanes) (239-241). Like the sesquiterpene isothiocyanates, most of these compounds were isolated along with the corresponding isocyanate and formamide compounds. 

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