Diterpenes reduction

The exchange of aromatic protons can be effected in the absence of any -OH or —NH2 activating group during the course of a Clemmensen reduction in deuteriochloric and deuterioacetic acid mixture (see section Ill-D). This reaction has been carried out with various tricyclic diterpenes and is best illustrated by the conversion of dehydroabietic acid into its 12,14-d2-labeled analog (40 -+ 41).Amalgamated zinc is reportedly necessary for the exchange reaction since the results are less satisfactory when a zinc chloride-mercuric chloride mixture is used. 

Deuteration of a Diterpene Carbonyl Compound by Clemmensen Reduction... 

Deuteration of a diterpene carbonyl compound by Clemmensen reduction, 170... 

The diterpenes andrographolide, andrographiside and neoandro-grapholide isolated from A. paniculata were also investigated for their protective effects on hepatotoxicity induced in mice by carbon tetrachloride or /ert-butylhydroperoxide ( BHP) intoxication by Kapil et pretreatment of mice with the individual diterpenes at a dose of 100 mg/kg, i.p. for 3 consecutive days were observed to produce significant reduction in malondialdehyde formation, reduced glutathione (GSH) depletion and... 

Leafy Spurge Root Extractives. Prior chemical examinations of leafy spurge have considered only aerial portions of the plant. Our recent chemical examination of root material relative to mammalian toxicity and/or allelopathy (29) resulted in the isolation and characterization of two new jatrophane diterpenes (esulone A (IX) and esulone B (X)) from the ether extract of the roots. Biological assay of esulone A showed it to be moderately phytotoxic (29% root length reduction (lettuce seeds) at 250 ppm), moderately toxic (LD50 78 23 mg/kg) and mildly Inflammatory (10 5 to 10 M, dermal) to mammals with no hyperplasia. 

In similar fashions, the core pathway up to C25 compounds (five isoprene units) is formed by sequential addition of C5 moieties derived from IPP to a starter unit derived from DMAPP. Thus, sesquiterpenes are formed form the precursor 2E, hS-farnesyl pyrophosphate (FPP), and diterpenes from 2E, 6E, IO -geranylgeranyl pyrophosphate (GGPP). The parents of triterpenes and tetraterpenes are formed by reductive coupling of two FPPs or GGPPs, respectively. Rubbers and other polyisoprenoids are produced from repeated additions of C5 units to the starter unit GGPP. 

Deuteration by reduction with lithium aluminum deuteride, 205 Deuteration of a diterpene, 170 Deuteration of double bonds, 179 Deuteration of estradiol, 157 Deuteration of 5a-pregn-9-en-12-one, 155 Deuteration with deuteriodiborane and hydrogen peroxide, 193... 

The uac of OB - ion to effect reduction of various a./J-upnxA ketones to a 0-unsaturated ketones was explored by Cole and Julian 3 with several simple epoxides. Particular success has been encountered with this technique. (Eqa. 426a and 426b), however, in the sroroid field.277 A paper by Barton and co-workers also describes tliia method in connexion with the reduction of a tetrasubstituted < - epoxy ketone diterpene. ... 

Cyeloalkenes (8, 483). The last step in a synthesis of flexibilene (2), a 15-membered-ring diterpene, involved cyclization of the keto-aldehyde 1, catalyzed with the active titanium metal prepared by reduction of TiClj with Zn-Cu in DME. A mixture of two cyclized products is formed, in which 2 is the major constituent.1... 

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). 

R. maritima.K The diterpene 3 gave 1 by reduction with NaBH4 and compound 1 gave 2 by acetylation. These chemical correlations (Scheme 2.1) confirmed the structure assigned on the basis of spectral data. 

This stereocontrol is useful in a synthesis of a spatanc diterpene (5). Thus hydride reduction of 3 affords only 4. In this case the vn-influcnce of the hydroxyl group is... 

Reduction of the oxazolidine ring. Sodium cyanoborohydride (CH3OH, pH 6-7, 25°) reduces the oxazolidine ring of various Cao-diterpene alkaloids almost quantitatively and completely selectively in the presence of a keto or an a,/3-unsaturated keto group. 

It is of considerable Interest to find that t-butyl esters may be reduced satisfactorily, in contrast to aliphatic t-butyl esters, which are cleaved to acids under Birch conditions. Also noteworthy is the regio-selective reduction of the ester (136 Scheme 24), in marked contrast to the reduction of the corresponding acid. Hydronaphthoate esters (137), (138) and (139) have been prepared (Scheme 25) and are envisaged as useful intermediates for diterpene synthesis. 

The configuration of the produced diol is influenced by the relative stabilities of the benzyl- or alkylcarbonium ions formed during the reaction. Similar reactions were investigated earlier. The rate and stereochemistry of the diborane reaction is altered by a small quantity of LiCl. Wide-ranging research has been performed with regard to the mechanism and stereochemistry of the diborane reduction in connection with cyclic and aliphatic a, 3-unsaturated and allylic epoxides, on diterpene models, " and by study of the reduction of epoxy-methylenecyclohexane and 2,3-epoxy-3-methylcyclohexanone. ... 

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