Dihydroxyserrulatic acid

The procedure has been used in a variety of syntheses of natural products [143, 144] for example, in the synthesis of dihydroxyserrulatic acid (Scheme 2-50) [145], the aggregation pheromone of Cathartus quadricollis (quadrilure) [146], and aza-C-disaccharides [147]. 

Serrulatanes The most common diterpene skeleton found in Eremophila is that represented hy the hicarbocyclic serrulatane group of compounds (101-104). Essentially, these are isoprenologues of the calamenene sesquiterpenes in which the dimethylallyl derived unit of the acyclic precursor does not participate in cyclisation. The first example of this skeleton was found in dihydroxyserrulatic acid (120) which was isolated from E. serrulata (101). As observed for the calamenenes, the presence of the serrulatane skeleton can be inferred from nmr spectroscopic data. 

The structural elucidation of dihydroxyserrulatic acid (120) required evidence for the tetralin ring and the relative arrangement of the substituents around it. To this end, the dimethoxy derivative was deoxygenated at Cl6 and the resulting compound was dehydrogenated with DDQ to provide a naphthalene (121). The orientation of substituents on the aromatic ring and the stereochemistry of the side chain double bond was inferred from spectroscopic analysis. Confirmation of the structure and the relative stereochemistry of the three asymmetric carbons was obtained by an X-ray diffraction study of 120. The absolute stereochemistry was determined by conversion of the methoxy naphthalene (121) to 5-(-)-4-(l, 5 -dimethylhexyl)-l,6-dimethylnaphthalene (122) which proved identical to, except for the sign of optical rotation, a synthetic sample of the / -enantiomer (123) prepared from / -citronellal (Scheme 29) (102). 

Many other serrulatanes have been isolated from different species of Eremophila (77,103-105). A number contain an asymmetric carbon atom at C15 (eg 124), the configuration of which was determined by X-ray diffraction methods (106). Apart from the oxygenation sites in dihydroxyserrulatic acid, others are observed at C2, C5, C7, C13, Cl8 and C20. The structurally more interesting serrulatanes include biflorin (125) from E. latrobei (104), an antibiotic originally... 

Scheme 11 Synthesis of ( )-dihydroxyserrulatic acid (rac-66) according to Uemura...

Marrubiin, T37.2 Callicarpone, T33.il Salvin, T33.17 Petasin, T"23.8 Contracted cembrane, T"30.4 7,8-Epoxy-14-hydroxy-3,ll,15-cembratien-17,2-oUde, T"31.14 Nivenolide, T"33.1 Dihydroxyserrulatic acid, T"33.3... 

Retinoic acid, 38B, 568 Cleomeolide lactone, 46B, 560 Lobophytolide, 43B, 711 Dihydroxyserrulatic acid, 43B, 712... 

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