Axisonitrile

Isonitriles are stable, often naturally occurring, compounds that contain a divalent carbon. An example is axisonitrile-3, which can be isolated from a species of sponge and possesses anti-malarial activity. Write a resonance form for axisonitrile-3 that satisfies the octet rule. Don t forget to include formal charges. 

The first marine isocyano metabolite was appropriately named axisonitrile-1 (1) based on the trivial name isonitrile and the genus of the sponge, Axinella cannabina, which also furnished axisothiocyanate-1 (2) [1] and, subsequently, a minor constituent, axamide-1 (3) [5]. This observation that isonitriles are often accompanied by isothiocyanates (-N=C=S) and formamides (-NHCHO) was later duplicated by the Hawaiian researchers working with a Halichondria sp. In... 

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. 

Further examination of the extracts of A. cannabina revealed axisonitrile-4 (7), axisothiocyanate-4 (8) and axamide-4 (9) [33], A vinylic isonitrile function was supported by H NMR signals at <51.67 and 1.89, which were assigned to the two isopropylidene methyls of 7. Difficulty in isolating the natural product 9 was circumvented, when isonitrile 7 was transformed to 9, mp 81-84 °C, by acetic acid in anhydrous ether. The absolute configurations of both axanes 1 and 7 and their analogs were later established [31] by studies including X-ray diffraction of the p-bromoaniline derivative of 2 and by CD data of ( + )-10-methyldecalone-l obtained from ozonolysis of the reduction (Na/NH3) product of 1 [1]. 

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],... 

Reviews of the syntheses of marine natural products, including marine isonitriles, have appeared recently [72]. After the early synthetic challenges of the tricyclic 9-isocyanopupukeanane (76) [73, 74] and 2-isocyanopupukeanane (78) [75] were met in 1979, additional syntheses of marine isonitriles were reported during 1986-1991. These were ( )-7,20-diisocyanoadociane (95) [63], ( )-axisonitrile-1 (1) and ( )-axamide-l (3) [76], the axisonitrile-4 triad (7-9) [78], and ( )-8,15-diisocyano-ll(20)-amphilectene (96) [79], and theonellin isocyanide (85) [80],... 

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. 

The electron is the smallest thinkable nucleophile which—generated from lithium in ethylamine—is even able to open certain unactivated vinylcyclopropanes (equation 142) the spiro[4.5]decane so obtained could be converted into the isocyanide sesquiterpene (— )-axisonitrile-3, which has the opposite absolute configuration of a marine sponge constituent . ... 

Isocyanide-containing natural products are rare they have been reported only from cyanobacteria, Penicillium fungi, marine sponges, and nudibranchs. Sesquiterpenoid and diterpenoid isocyanides are found in a limited species of sponges and nudibranchs that prey on these sponges. Axisonitrile-1 (106) isolated from Axinella cannabina is the first isocyanide-containing marine natural product. ... 

Axisonitrile-3 (20) A. cannahina Topscntia sp. A klcthra A cavernosa P oceUata unidentified sponge A aplysmoules P. pustulosa llaly Thailand Australia Australia Japan Japan Pohnpei Pohnpei Japan 37 45 44, 48 43 13 13 9 10 1 1 see ref. 113... 

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