TRACHYLOBANE

Source Helianthus niveus (A.Gray) Heisev Mol. formula C2QHgg02 Mol. wt. 318 Solvent CgDgN 

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Leong, Y.-W. and Harrison, L. J. 1997. ent-Trachylobane diterpenoids from the liverwort Mastigophora diclados. Phytochemistry 45 1457-1459. 

The deketalization-retroaldol-aldol procedure was applied to compound (100). Acid catalyzed deketalization, followed by the retroaldol-aldol process afforded (101), which could be transformed to the diterpene trachylobane (102)31>. 

In Bettolo and co-workers approach to (+)-methyl trachyloban-18-oate (16), enone 13 was subjected to a photocycloaddition with 1,2-propadiene (1) to afford the [2 + 2]-cycloadduct 14 as a single product in 67% yield (Scheme 19.3) [5]. The addition proceeded exclusively from the /3-face. The resulting exocyclic olefin was eventually converted to a ketone using osmium tetroxide and NaI04 and taken on to 15, constituting a formal total synthesis of 16. 

Scheme 19.3 A formal total synthesis of (+)-methyl trachyloban-18-oate.

Varieties of sunflower (Helianthus annums, Asteraceae) that are resistant to attack by larvae of the sunflower moth (Homeosoma electellum) contain high concentrations of trachyloban-19-oic acid and (-)-16-kauren-19-oic acid in their florets (84,132). 

Bicycloannelation.1 The a -enolate of an a,j -cyclohexenone reacts with this phosphonium salt to form a tricyclof3.2.1,0 ]octane in low to moderate yield. This reaction was used in a short synthesis of the pcntacyclic dilcrpcnc trachyloban-19-oic acid (4). Reaction of the lithium enolale of 2, prepared from podocajpic acid, with I provided the pcntacyclic ketone 3, which was reduced by the Wolff-Kishncr reaction to 4. 

Ferguson, G., McCrindle, R., Murphy, S. T., and Parvez, M. 1982. Further diterpenoid constituents of Helianthus annuus I. Crystal and molecular-structure of methyl-er7M5-beta-hydroxy-trachyloban-19-oate. J. Chem. Res.-S.t 8, 200-201... 

Pyrek, J. S. 1970. New pentacyclic diterpene acid trachyloban-19-oic acid from sunflower. Tetrahedron 26, 5029... 

The trachylobane ring system has been synthesized by homoallylic reduction of the atisene mesylate (83) with lithium aluminium hydride.79 The structure of many of the... 

Four structural types of diterpenes are known from Helianthus labdanes, kauranes, atisiranes and trachylobanes (Figure 2), with the tetracyclic kaurane type being the most widespread in the genus. The majority of Helianthus diterpenes have an Ol-oriented carboxylic acid function attached to carbon 4. 

Kaurenoid Diterpenoids Beyerene Diterpenoids Atiserene Diterpenoids Trachylobane Diterpenoids Gibberellins Grayanotoxins Diterpenoid Alkaloids... 

Trachylobanes.—Trachyloban-19-oic acid (92), together with ( —)-kaur-16-en-19-oic acid, has been isolated from Helianthus annuus. The structure was confirmed by the use of n.m.r. shift reagents. 

Sideritis canariensis contains trachylobane, (—)-kaurene, and some 7)S,18-dihydroxy-( — )-kaur-16-ene, together with trachinodiol [(7fi, 18-dihydroxytrachyl-obane (93)] and trachinol (7)5-hydroxytrachylobane). The structure of trachinodiol was established by interconversion with trachylobane. Oxidation gave a keto-ester, which on bromination and dehydrobromination afforded an a -unsaturated ketone whose substitution pattern located the carbonyl group at C-7. 

The asymmetric syntheses of (-)-methyl kaur-16-en-19-oate and (-)-methyl trachyloban-19-oate was achieved by M. lhara and co-workers. One of the last transformations was the deoxygenation of the ketone carbonyl group of the tetracyclic intermediate, which was effected by the Wolff-Kishner reduction. Under the strongly basic conditions the ester functionality was hydrolyzed, so an esterification using diazomethane was necessary as the final step. The major deoxygenated product was (-)-methyl kaur-16-en-19-oate (59%). The minor product was identified as (-)-methyl trachyloban-19-oate (16%). 

Methyl kaur-16-en-19-oate (-)-Methyl trachyloban-19-oate... 

N-Tosylazetidin-2-imines, 60 Tosylhydrazones, 47 N-Tosylketenimines, 60 Tosylmethylisocyanide, 409 Trachyloban-19-oic acid, 225 Transsilylation, 62... 

Mesylation of annulated bicyclo[2.2.2]octenol 29 in the usual way initiates a spontaneous cationic cyclization to trachylobanate alcohol 30 in 40% yield. Mesylation followed by addition... 

Treatment of c t-trachyloban-19-oate 8 with thallium(III) acetate in acetic acid resulted in cleavage of the most strained bond of the three-membered ring to afford the corresponding diacetate together with elimination products. ... 

The carbon skeleton of the ent-kaurenoid precursors of the gibberellins is closely related to that of the diterpenoids of the ent-atiserene (10.29), ent-beyerene (10.30) and ent-trachylobane (10.31) series. The dilferences lie in the structure of ring D. The flexibility of the gibberellin biosynthetic pathway in... 

Herz et a/.70e used this catalytic method for the conversion of (7) into (8), ( )-methyl trachylobanate, a member of a new class of pentacyclic triterpenes discovered by Ourisson et al.im... 

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