Guaianolide sesquiterpenes

Achalensolide (guaianolide sesquiterpene lactone) Dehydroleucodin (germacranolide sesquiterpene lactone)... 

Dihydrogriesenin (seco-guaianolide sesquiterpene lactone) Geigeria africanum (Asteraceae) Ox. Phos. [toxic]... 

Methylenation. In a synthesis of the two guaianolide sesquiterpenes dehydrocostus lactone (4) and estafiatin (6), usual methods for methylenation of the ketone group of 2 resulted only in p-elimination. However, use of the anion of 1 effected the desired reaction, albeit in modest (15%) yield. 

The subsequent transformation of these cycloadducts further illustrates the versatility of this approach in the construction of guaianolide sesquiterpenes (Scheme 1)7 The moiety incorporated in the adduct allows for the introduction of diverse functionalities at C-S and C-2. For example, reduction of the cycloadduct (11) with sodium borohydride produces a good yield of the iron complex (16). Oxidation of this complex with cerium ammonium nitrate gives methyl ester (17). In addition, (11) reacts with nucleophiles such as lithium dimethylmalonate and methanol to give the alkylated complex (18) and the meth-oxylated complex (19), respectively. Oxidative demetallation of (11) with bromine leads to selective replacement of the moiety at C-2 by bromide. ... 

The oxabicyclo[3.2.1]octan-2-one ring systems form a core skeleton of many naturally existing molecules. In an approach towards guaianolide sesquiterpenes, their hydroazulenic framework has been constructed through a rhodium(II)-catalyzed reaction [82] of the a-diazo ketone 106 with DMAD to afford the oxatricyclic system 107, which forms the skeleton of ambrosic acid 108 (Scheme 33). 

Scheme 14.23 Rodriguez and Coquerel s approach to guaianolide sesquiterpene iactones via MARDi reaction.

A guaianolide sesquiterpene lactone extracted from costus oil. Dehydrocostuslactone is one of the components of lactone-mix, with costunolide and alantolac-tone, used to detect Compositae-sensitive patients. 

Rodriguez, A.D. and Boulanger A. (19%) Americanolides A-C, new guaianolide sesquiterpenes from the Caribbean sea plume Pseudopterogorgia americana. J. Nat. Prod., 59,653-657. 

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