Axane skeleton

Sesquiterpenoids based on the axane skeleton (354) have been reported previously as metabolites of marine sponges or algae (cf. Vol. 5, p. 77 Vol. 6, p. 89). Further investigations in this area have revealed the presence of axisonitrile-4 (355), axisothiocyanate (356), and axamide-4 (357) in the sponge Axinella cannabina. These compounds are A -derivatives of known metabolites (axisonitrile-1 etc.) of this sponge and are included in this section because their biosynthesis may involve rearrangement of a eudesmane precursor. 

Axisonitrile-1 (1) and axisothiocyanate-1 (2) were the first pair of NC/NCS compounds isolated from Axinella cannabina, see Introduction [1]. That both compounds possessed a new skeleton was evident, when 1 was reduced (Li/EtNH2) to axane (6). Other transformations involving the exocyclic methylene which survived selective reduction (Na/NH3) of 1, coupled with evaluation of the lHNMR data, supported its gross structure. Confirmation of 2 was secured when 1 was heated with sulfur and the resultant purified product found to be identical to the natural product. 

These compounds range through monocyclic (with a bisabolane framework), bicyclic (with an eudesmane, amorphane, axane, guaiane, isodaucane, or gorgonane framework), tricyclic (with an aromadendrane, cubenane, maaliane, pupukeanane, or trachyopsane framework), and spiro[4,5]decane carbon skeletons. 

The Axinella sponges produce several types of isonitriles based on different sesquiter-penoid skeletons. The main type is exemplified by axisonitrile-1 (128), which was the first marine isonitrile to be reported and was also the first example of the axane class of Cl 5 compounds. The same sponge also produces axoisonitrile-2 (129) , the spiroxane 130229,230 131231 Acanthdla spp in the same Order in contrast yield Cis-based iso-... 

One point about isonitriles and isothiocyano and N-formylamino derivatives concerns the fact that they have always been observed on terpenic skeletons, to the exclusion of any other supporting structure. In addition, nearly 150 molecules are now known and ah are either sesquiterpenes or diterpenes. The carbon skeletons are numerous and often original, such as axane, spiroaxane, pupukeanane, amphilectane and cycloamphilectane. Most of these skeletons are presented in Figure 19.54. 

---