Diterpenes diene

Compound (51) appeared to come from a Diels-Alder reaction between a diterpene diene and ochraceolide A as a dienophile. The possibility of the presence of enzymatic system with hetero or Diels-Alderase activity in Celastraceae was suggested once again, based on the structure of (51)... 

The use of ultrasonic (US) radiation (typical range 20 to 850 kHz) to accelerate Diels-Alder reactions is undergoing continuous expansion. There is a parallelism between the ultrasonic and high pressure-assisted reactions. Ultrasonic radiations induce cavitation, that is, the formation and the collapse of microbubbles inside the liquid phase which is accompanied by the local generation of high temperature and high pressure [29]. Snyder and coworkers [30] published the first ultrasound-assisted Diels-Alder reactions that involved the cycloadditions of o-quinone 37 with appropriate dienes 38 to synthesize abietanoid diterpenes A-C (Scheme 4.7) isolated from the traditional Chinese medicine, Dan Shen, prepared from the roots of Salvia miltiorrhiza Bunge. 

Diels-Alder reaction of the furan derivative 148 with homochiral bicyclic enone 149 is the key step [56] in the total synthesis of the diterpenes jatropho-lone A and B, 151 and 152, respectively, isolated from Jatropha gossypiifolia L [57], Initial efforts to carry out the cycloaddition between 148 and 149 under thermal or Lewis-acid conditions failed due to diene instability. Application of 5kbar of pressure to a neat 1 1 mixture of diene and dienophile afforded crystalline 150 with the desired regiochemistry (Scheme 5.23). Subsequent aromatization, introduction of the methylene group, oxidation and methylation afforded (-l-)-jatropholones 151 and 152. 

The GC-MS data (Figure 16.11) of the violet zone of B. carterii revealed that the unchanged diterpenes (verticillatriene, cembrene A, and cembrene C) and the nortriterpenes with carbohydrate structure originated from the pyrolyzed triterpenes (Figure 16.12) of the a- and (3-boswellic acids, named 24-norursa-3,12-diene (compound 7), 24-norursa-3,9(ll),12-triene (compound 8), 24-noroleana-3,12-diene (compound 9), and 24-noroleana-3,9(ll),12-triene (compound 10). 

We focused our attention on Tall oil, a by-product of the paper industry, whenever this is prepared according to the KRAFT process. Said material consists of a mixture of highly unsaturated fatty acids (many of which with conjugated diene systems) and terpene derived rosin acids. The rosin acids have the molecular formula C20H30O2 and thus belong to the diterpenes (pimaric and abietic acids). Tall Oil has an iodine number equal to approximately 170 gl2/100 g. 

The apparently latest total synthesis of a dolastane diterpene was published by Williams and coworkers in 1993 as a short communication (Fig. 16) [91]. (-)-Clavulara-l(15),17-dien-3,4-diol (129) was synthesized using a strategy that relied on the availability of the enantiomerically pure building block 162 from (+)-9,10-dibromocamphor (163) (Fig. 16). Cornerstones of the synthesis are a macrocyclization that afforded the 11-membered (A+B)C-ring (160) and a transannular cyclization that converted a bicyclic into a tricyclic ring system. Two of the seven chirality centres in the synthetic clavu-... 

The route could start from the mixture of cis- and /rans-communic acids (or also from other diterpenes, such as isocupresic acid). The isolation of hydroxyacid I as a natural product from Acrostalagmus reinforces the possiblity of the existence of diene II as a key precursor, not only of isoacrostalidic acid and acrostalidic acid, but also of dilactone III. The straightforward chemical conversion of I into III in a recent publication by Barrero et al. [20] supports this hypothesis. 

A Japanese sponge of the Adociidae family contained 10-isothiocyanatobiflora-4,15-diene (290), which was identified by spectral analysis [283], A. cavernosa from Fiji yielded a diterpene isothiocyanate (291) [284]. 

Compounds 237 and 238 are the only isothiocyanate diterpenes with a biflorane carbon skeleton that do not belong to the kalihinol family. They are diastereosiomers of 10-isothiocyanatobiflora-4,15-diene. A planar structure was reported for compound 237, which was obtained from an unidentified sponge of the Family Adocidae [191]. A... 

Shibasaki and co-workers have described a regioselective Heck cyclization of aryl triflate 12.1, which ultimately provides tricyclic enone 12.4, a key intermediate in a number of diterpene syntheses (Scheme 8G.12) [25], Treatment of 12.1 under typical cationic conditions resulted in preferential 6-exo closure to give 12.2 and 12.3 as a 3 1 mixture in 62% overall yield and with 95% ee for both products. The complete selectivity for 6-exo cyclization is noteworthy because 6-endo, 5-exo, and 7-endo cyclization modes were also possible. An analysis of the steric interactions involved in the various cyclization modes was presented and was used to rationalize the observed selectivity. Non-conjugated diene 12.2 could be isomerized to the fully conjugated diene 12.3 in quantitative yield by using catalytic naphthalene Cr(CO)3. Both Heck products could be converted to the enone 12.4,... 

Polyene cyctization.1 The reaction of C6H5SOCH3 and BF3 with the diene 1 in CH3N02 initiates cyclization to the tricyclic ring system 2 via a sulfenium ion. This product was converted to the diterpene nimbidiol (3) by reductive desulfuration (lithium naphthalenide) and oxidative decyanation (SnCl2), and demethylation (BBrj). 

Diels-Alder catalyst.1 A novel, general route to tricyclic diterpenes involves a Diels-Alder reaction between a hindered diene such as I and a 1,4-benzoquinone. 

Lin,X., Hezari, M., Koepp, A.E., Floss, H.G. and Croteau, R. (1996) Mechanism of taxa-diene synthesis, a diterpene cyclase that catalyzes the first step of taxol biosynthesis in Pacific yew. Biochemistry, 35,2968-77. 

DIENES Dichloromalcic anhydride. DITERPENES Palladium catalysts. OLEFINS Cuprous chloride. Lithium di-phenylphosphide. Lithium orthophosphate. Potassium r-butoxide. Thiophe-nol-Azobuty toni tide. OXASPIROPENTANE Lithium iodide. 

Taxol is biosynthesized in 19 steps from GGPP that originates from precursors of the MEP pathway (Fig. 5). The biosynthesis of Taxol begins with the formation of the tricyclic diterpene skeleton of taxa-4(5),ll(12)-diene (17, 39). All genes for the enzymes in this early pathway have been identified in Taxus cuspidata and a taxa-4(5),ll(12)-diene synthase has been identified in several Taxus species. The mechanism of this di-TPS has been explored in detail (39). Taxa-4(5),ll(12)-diene is then hydroxylated by several cytochrome P450 taxoid oxygenases to yield a putative intermediate decorated with seven alcohol... 

Pimarane diterpenes with an antipodal backbone have been isolated from Cleistanthus schlechteri. These included ent-3)8-hydroxypimara-8,l5-diene, ent-3)3,12 -dihydroxypimara-8,l 5-diene (16), and the corresponding C-12 ketone. The location of the carbonyl group at C-12 was inferred from bromination and dehydrobromination and from the multiplicity of the C—H resonance of the C-12 alcohol. Macarangonol (17) has been isolated from Macaranga tanarius. 

A number of partial syntheses which have been mentioned earlier in this chapter e.g. rosenonolactone), may be considered as formally total by virtue of the previous synthesis of an intermediate. The compound (124) features as an intermediate in diterpene total synthesis. Alkylation with methyl iodide gave a mixture of C-13 epimeric aldehydes which were converted " into pimara-8(14),15-dien-19-oic acid and its C-13 epimer the former occurs in Aralia cordata. 

Besides sulphated PS, reports on anti-HSV compounds isolated from marine algae are recorded in the literature. Specimens of the brown alga Dictyota pfaffii from Atol das Rocas, northeast Brazil, afforded the rare dolabellane diterpene 10,18-diacetoxy-8-hydroxy-2,6-dolabella-diene and the new 10-acetoxy-8,18-dihydroxy-2,6-dolabella-diene [46]. These substances showed strong anti-HSV-1 activity in vitro. Several antiviral diterpenes were isolated from other brown algae of the Dictyota genus. 

In our knowledge, 2,6-dimethyl-10-(p-tolyl)undeca-2,6-(E)-diene (1) is the alone monocyclic diterpene, it was reported from S. dorisiana [39]. 

In the laboratory of J.H. Rigby, synthetic studies were undertaken on the ingenane diterpenes. During these studies, it was necessary to investigate the ring opening reactions of a structurally complex allylic epoxide intermediate. This allylic epoxide was prepared from a 1,3-diene in three steps dihydroxylation, epoxidation and Corey-Winter olefination. 

The ABCD ring system of the diterpene alkaloid atisine was constructed by T. Kametani et al using an intramolecular Diels-Alder cycloaddition reaction as the key step. The dienophile was obtained by the traditional Hofmann degradation of the corresponding dimethylamino precursor. The diene was prepared by the kinetic enolization of the cyclohexenone system with LDA. 

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