Antifungal diene

The levels of antifungal diene in the pericarp of whole avocado fruits could be increased by exposure to ethylene (40 pl/1) during 3 h. The diene content of the extracted pericarp increased by 50% 6 h after ethylene removal. Similar results were obtained at 35°C. 

The lack of response by pericarp alone suggests that avocado mesocarp may be responsible for the changes in the diene levels in the pericarp. Idioblast oil cells from avocado mesocarp are also susceptible to stimulation the effect of ethylene on their antifungal diene induction is time and temperature dependent. 

Idioblasts but not their lipid environment are responsible for the increased production of antifungal diene. They seem to export the diene towards their surrounding medium. 

Prusky, D., Keen, N., Sims, J. J. and Midland, S. L. (1982). Possible involvement of an antifungal diene in the latency of Colletotrichum gloeosporioides in unripe avocado fruits. Phytopatology 72, 1578-1582. 

Also the novel antifungal antibiotic (-)-PF1163B (211), isolated from Strep-tomyces sp., which features a 13-membered macrocycle incorporating both a lactone and a lactam unit, was synthesized by an RCM route (Scheme 42) [101]. While only poor results were obtained by treatment of diene 210 (containing 8% of an unidentified epimer) with catalyst A, the use of NHC catalyst C led, under the conditions outlined in the scheme, to the corresponding cyclization product in 60% yield along with 10% of a diastereomer resulting from epimer-ization in a previous step. 

The asymmetric hydroformylation of a 1,3-diene has been recently used in the course of a total synthesis of the antifungal natural product ambruticin. The retrosynthesis as well as the hydroformylation key step are depicted in Scheme 25 [75]. 

Higher molecular weight dienes and polyenes which are solid and can be crystallized make it possible to study their structure by X-ray diffraction. This, of course, will give information only about the crystalline form (see discussion on steroids and antifungal molecules, Section VII). 

A formal synthesis of the antifungal agent alternaric acid was realized in the Trost group.95 The skipped diene portion of the natural product was obtained via a ruthenium-catalyzed intermolecular Alder-ene reaction (Scheme 36). Several attempts to produce 162 from the protected fragment 161 gave low yields and unremarkable regioselectivity. The diol (R = H), however, performed satisfactorily, allowing the reaction to be carried out at room temperature. The product 162 was obtained in 51% isolated yield as an 8.9 1 mixture of branched to linear isomers. 

The Wittig reaction was employed to fuse diene 49 and aldehyde 50, in the final stages of the stereoselective synthesis of epothilone B, a macrocyclic compound with potential antifungal properties (equation 31)49. 

If the precursor dienes have vinyl end-groups, ethene is eliminated in the metathesis reaction, but it is sometimes advantageous to use a precursor with one or two propenyl end-groups, eliminating propene or but-2-ene in the metathesis reaction. An example is shown in equation 31, the final stage in the synthesis of the protected precursor (42) of Sophora compound I, the antifungal phytoalexine isolated from the aerial part of Sophora tomentosa L228. 

A simple example is the synthesis of analogues of the antibiotic and antifungal streptazolin by Cossy.40 Enantiomerically pure diene carbamate 188, prepared from the chiral pool (see chapter 23 and the workbook for this chapter) was treated with the Grubbs catalyst to form the six-memberedring 189 required for (-)-4,5-dihydrostreptazolin 190. This metathesis product inevitably contains a Z-alkene. 

CisH BrjClOj, Mr 424.56, colorless cryst., mp. 165-167°C, [a]D -257.6° (CHCI,). The allene O. I was first isolated from the alga Laurencia obtusa but also occurs in other Laurencia species. It is accompanied by numerous other halogenated Cjj-Cjo fatty acid derivatives with antifungal activities. O. exists as the 3,13-dioxabicyclo[7.3.1]trideca-5,9-diene as a result of the formation of ether bridging bonds. 

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