Manoyl oxide isomer

The study of manoyl oxide derivatives i.e. 7 and 8 in, Fig (7), (i.e ent-hydroxy and en/-acetoxy-3(3-manoyl oxides) isolated from Cistus creticus, by GC-MS resulted in only one peak indicative of the purity of the products [33]. From the H-NMR data it is clear that the 13-epi isomer was present in both derivatives [58,139]. The chromatographic data of the compounds 7 and 8 were recently published [33,63]. Hence, investigations have proven that, apart from the 13-epi isomer, there are more isomers with varying intensities, which correspond to isomers that arise from the different configuration of C-8 chiral center [33]. This isomer showing a different configuration at C-8 has been isolated from the volatile leaf oil of Alaska (yellow) cedar and its structure has been confirmed using spectroscopic methods as well as chemical reactions [150],... 

The formation of a common manool trihydrochloride from manool, sclareol, manoyl oxide, 13-epimanoyl oxide, biformene, and abienol played an important part in the structural correlation between these diterpenes. Earlier proposals had suggested an 8-equatorial chlorine atom, but in a paperclarifying the various 8,13,15-chloro-labdanes, the analogous monohydrochloride from tetra-hydroabienol was assigned the 8-axial stereochemistry (8). Dehydrochlorination of this isomer yields all three expected olefins, whilst the equatorial epimer affords only the and A -olefins. 

The oxidation of manool has been re-examined with the aim of producing ambergris-type perfumes. Oxidation with potassium permanganate afforded the known s methyl ketone (6), the diether (7), and at 40 °C the lactone (8). Sodium dichromate gave the aldehyde (9) as a mixture of E- and Z-isomers. Further oxidation of the methyl ketone with hypobromite gave an a-hydroxy-acid (10) and an ether (11) which was also obtained from manoyl oxide. Oxidation of the ketone with per-acid gave an acetoxy-epoxide which on reduction with lithium aluminium hydride afforded a diol. This was converted into an odoriferous ether (12). The ready formation of 5- and 6-membered-ring ethers of this type is a characteristic feature of this area of diterpenoid chemistry. 

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