Virescenol

The X-ray analysis of the y-lactone (79) formed by acid treatment of dihydroisopimaric acid has shown that it possesses a trans a/b ring junction, in contrast to some previous structural assignments. The solvolysis of virescenol B... 

The Favorskii-type rearrangements of chloroenamines such as (31) have received some investigation, and key results are presented in Scheme 45. Finally, the so-called homo-Favorskii rearrangement has been probed, and an example from the original work of Wenkert and coworkers is illustrated in Scheme 46. A partially successful homo-Favorskii rearrangement carried out on the diterpenoid (32 a derivative of virescenol A) is shown in Scheme 47, but the synthetic potential of this variant of the Favorskii rearrangement remains to be established. 

The stereochemistry of the SNi cyclization in the biosynthesis of ent-sandaraco-pimaradiene74 and virescenol B75 has been studied using stereospecifically... 

Chemistry of the Tricyclic Diterpenoids.— The conversion of virescenol A (66 R = OH) into virescenol B (66 R = H) was complicated by the ease of 2,19-ether formation. In the event the transformation was achieved through hydro-genolysis of the keto-furan (67). The chirality of nucleophilic reactions at the C-4 axial aldehydes and methyl ketones has been examined in the podocarpane series. The reaction of some ring B enol-acetates with thallium(l) acetate and iodine has been studied.lodination at the 6a-position is followed by elimination to form a/8-unsaturated ketones. 

The 1-and 9-hydroxyl groups define an important area for forskolln s action. The 1,9-dideoxyderlvative (7 ) is totally Inactive and the 1,9,6,7-dicarbonate ( ), and 1,9 sulfonate are very weak at activating adenylate cyclase. Other structurally related compounds which are unable to activate adenylate cyclase are 1,6-dlketoforskolin, the 14,15-oxide (12), virescenol-B, abietic acid, podocarpic acid, retene, glbberellln, and other diterpenes(13-15).23,83 Mone of the inactive dlterpenes antagonize forskolln stimulation of adenylate cyclase. Derivatives of... 

Virescenoside C is the jff-D-altropyranoside of virescenol C (26), a metabolite of Oospora virescens. - The carbon-13 n.m.r. spectra of a group of pimaradienes have been recorded and the resonances assigned. These results have been appliedto the study of the biosynthesis of the virescenosides q.v.)... 

Two new metabolites, virescenosides D and H, isolated from the fungus Acre-monium luzulae (Fuckel) Gams have been identified, on the basis of chemical and spectroscopic evidence, as the 4,5-unsaturated glycosides (349) and (350X respectively. Two other metabolites, virescenosides E and L, isolated from this fungus differ from (349) and (350) in the nature of the aglycone (virescenol A instead of virescenol B). Enantiomeric forms of 9-(5-deoxy-p-eryt/iro-pent-4-enofurano-syl)adenine have been synthesized by way of dehydroiodination of appropriately protected 5 -deoxy-5 -iodo-nucleosides with DBU in DMF. ° ... 

Simple derivatives of 4,107) formed following a second cycliza-tion, are virescenols A (4.108) and B (4.109) and aphidicolin (4.110), Use, in particular, of [l,2- C2]acetate as precursor has established the biosynthetic pathway shown in Scheme 4.22 [99, 100]. t Detailed study has been carried out on the biosynthesis of the fungal metabolite, rosenonolactone (4.111). Acetate and... 

Cane D E, Hasler H, Materna J, Cagnoli-Bellavita N, Ceccerelli P, Madruzza G F 1981 NMR determination of the stereochemistry of an allylic displacement in the biosynthesis of virescenol-B. J Chem Soc Chem Commun 280-282... 

The biosynthesis of the virescenosides [o-altropyranosides of diterpenoid aglycones such as virescenol A (40)] from [1- C]- and [2- C]-acetate has... 

Bie stereochemistry of the cyclizatitHi in the biosynthesis of ent-sanadaracopimaradiene (33) has been examined with an enzyme system diich was prepared from Rioinus communis. Incubation of D(s)-1- 3s ylgeranyl pyrophosphate (3I) produced (b) - D 6 1-ent-3andaracopimaradiene (33), showing that the Sjj cyclization of the intermediate copalyl pyrophosphate (52) occurs wi-tti tine anti stereochemistry. Similar results have been obtained in the stereochemistry of tire allylic displacement of a pyrophosphate in the biosynthesis of virescenol B (34), It has also been suggested that the cyclization of copalyl pyrophosphate to ent-kaurene (55) follows the same anti pathway. 

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