Tricyclic diterpenoids

Some unusual rearranged tricyclic diterpenoids with a cis- a/b ring fusion have been isolated62 from Rondeletia panamensis (Rubiaceae). Panamensin has the structure (40) whereas its dihydro-derivative, rondeletin, has the 2-keto structure (41). 

Chemistry of the Tricyclic Diterpenoids.—The addition of chlorosulphonyl isocyanate to the methyl esters of levopimaric and neoabietic acids with the formation of C-12 carboxyamides has been described.63 The well documented aromatic substitution reactions of dehydroabietic acid continue to be examined,64 together 

Savard, M. Neron Desbiens, and R. H. Burnell, Synth. Commun., 1981,11, 399. 

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

Curini, P. Ceccherelli, R. Pelliceiari, and E. Sisani, Gazz. Chim. Ital., 1980,110, 621. 

Ozonolysis of dehydroabietic acid has been used to give keto-esters such as (68) which have been converted into sesquiterpenoid drimane derivatives. An 

Cagnoli-Bellavita, P. Ceccherelli, M. Ribaldi, J. Polonsky, Z. Baskevitch-Varon, and J. Varenne, J.C.S. Perkin I, 1977, 351 Gazzetta, 1977,107, 51. 

Tahara, Chem. and Pharm. Bull. (Japan), 1977, 25, 974. 

Various tricyclic diterpenoids have been shown to possess a hypocholes-terolemic action in test animals. 

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Figure 3.17 shows the mass profile of the resinous material collected from the Roman amphora. It shows the presence of abietane skeleton diterpenoids due to the occurrence of the peaks at m/z 315, 299, 285, 253 and 239. Furthermore, a high degree of oxidation of the resin was ascertained by the abundance of peaks at m/z 315 and 253, deriving from 7-oxo-dehydroabietic acid, and those at m/z 331 and 329, from highly oxidised tricyclic diterpenoid molecules. Finally, the presence of retene was evidenced by the peaks at m/z 234 and 219. The results showed that a pitch from Pinaceae had been in the amphora. 

Some new diterpenoid oxides have been obtained from Eupatorium jhanii. They are jhanol (12) and its 18-acetate together with jhanidiol (13) and its 18-monoacetate and diacetate. Their structures were established by correlation with manoyl oxide and by an examination of their C n.m.r. spectra. 11/3-Hydro-xymanoyl oxide (14) has been isolated from Juniperus oxycedrus ° A group of new 11-oxomanoyl oxide derivatives (15a—e) has been obtained from Coleus forskohlii (Labiatae). Their oxygenation pattern is reminiscent of that of the tricyclic diterpenoids which have beemobtained from other Coleus species. 

Tanshen (Salvia miltiorrhiza Bung), a medicinal plant, has been used in traditional Chinese medicine for its tranquilizing, sedative, circulation-promoting and bacteriocidal effects. [73], It has proven to be a rich source of abietane o-quinone diterpenoids. Miltirone (197) is a tricyclic diterpenoid quinone which has been isolated from the roots of salvia miltiorrhiza Bung. The isolation of miltirone constitutes a new addition to naturally occurring quinines related to tanshinones [74,75] isolated from the same source. 

The 13C n.m.r. resonances of a number of groups of diterpenoids have been assigned. These include tricyclic diterpenoids,4 the kaurenolides,5 and the gibberel-... 

Chemistry of the Tricyclic Diterpenoids.—The n.m.r. spectra of abietic acid... 

Cassane and Miscellaneous Tricyclic Diterpenoids The Chemistry of Ring A The Chemistry of Ring b The Chemistry of Ring c... 

Tricyclic diterpenoids were found in numerous species. They may be divided into 2 categories, pimaranes and abietanes. 

The cycloalkylation reactions of suitable arylalkyl carbinols leading to tricyclic diterpenoids have been examined for their synthetic and mechanistic significance, and the syntheses of some octahydrophen-anthrenes, such as in equation (107), have been reported. 

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. 

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