Chrysanthemyl skeleton

Car-3-ene is known to be a convenient starting material for access to the irregular chrysanthemyl skeleton (see Section 14). The (+)-olefin has been again stereo-specifically converted (via hydration and oxidation) into (+)-dihydrochrysanthemo-lactone and (+)-methyl m-chrysanthemate.667 668 Other 1,2-cis-cyclopropane derivatives have resulted from oxidative cleavage of derivatives of the same substrate.669-671... 

Crombie s group has also discussed the biogenesis of these monoterpenoids, giving examples of the various possibilities of the scission of the chrysanthemyl skeleton to the other skeletons, including the synthesis of the dehydrolavandulol (67) from a n s-chrysanthemic diol (68). They report some feeding experiments with C-labelled chrysanthemate, but incorporation into artemisia ketone was very low. The synthesis of a cyclopropyl terpenoid once discussed by Robinson as a possible biogenetic intermediate to artemisia ketone has been accomplished from nerol oxide it is discussed in the section on pyranoid monoterpenoids (below). 

The suggestion of an alternative non-mevalonoid route in monoterpenoid biosynthesis77 has received some support in the efficient incorporation of L-[l/- 4C]valine into the DMAPP moiety of linalool 78 a pathway via deamination to dimethylacrylic acid is proposed. L-Leucine and l-valine are also incorporated, at least in part, into the DMAPP moiety of geraniol (8) and citronellol.79 (lf ,3/ )-Chrysanthemic acid (25) is biosynthesized80 in Chrysanthemum cinerariaefolium from ( R,3R) chrysanthemyl alcohol (26) but not from precursors with the lavandulyl (27) or artemisyl (28) skeletons (Scheme 4) (li ,3R)-chrysanthemyl alcohol (26) has been... 

Unexpected results have come to light bearing on monoterpenoid biosynthesis (Chapter 1). Banthorpe s group have shown that in the formation of the thujane and camphor skeletons, activity from labelled mevalonic acid can appear predominantly in the C5 unit supposedly derived from isopentenyl pyrophosphate and only to a minor extent in the dimethylallyl pyrophosphate-derived portion. Banthorpe has also presented evidence for a chrysanthemyl intermediate, analogous to presqualene alcohol, in the biosynthesis of artemesia ketone. 

In the laboratory, however, the route from prenyl ethers or thioethers to artemisia compounds and thence to the santolina skeleton is possible, and an interesting conversion to the lavandulyl skeleton of prenyl compounds has been described. A mixture of 3-methylbut-2-enyl acetate (44) (or chloride) and 3-methylbut-2-enylthiol acetate (45) is treated with aluminium chloride or zinc chloride, when, in addition to the thioether (46), 19% of the lavandulylthiol acetate (47) and 6% of the corresponding isolavandulyl compound (48) are formed. An ingenious two-step synthesis of trans-chrysanthemyl alcohol (49) has also been achieved from prenyl alcohol (50) and 3-methylbut-l-yn-3-yl... 

Certain bacteria are able to form C3Q, C45, and CgQ-isoprenoids of the phytoene type in addition to phytoene by head-to-head condensation of appropriate precursor molecules. In higher plants certain monoterpenes probably are synthesized in a similar manner. Chrysanthemyl alcohol, occurring in Compositae, is an analog of presqualene and prephytoene. The C-skeletons given in Fig. 97 are derived from chrysanthemyl pyrophosphate. Chrysanthemum carboxylic acid is a constituent of the pyrethrins, compounds with marked insecticidal activity (E 5.5.3). 

The first step involves the intermolecular olefin alkylation between two molecules of dimethyl allyl pyrophosphate. A 1,3-proton elimination from the methylene group gives chrysanthemyl pyrophosphate while a 1,2-proton elimination affords the lavandulol skeleton. Of course, these transformations can be equally well represented by formation of either a bridged, non-classical carbonium ion or an intermediate covalently bound to a nucleophile (e.g., X group on an enzyme surface... 

Bates, R. B., and D. Feld Terpenoids. XIII. Conversion of Chrysanthemyl Alcohol to a Triene with the Artemesia Ketone Skeleton. Tetrahedron Letters 1967, 4875. 

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