Neoclerodanes from Teucrium orientale
Abstract Two new neoclerodane diterpenoids, 6-deacetyl-teucrolivin A (5) and 8beta-hydroxy-teucrolivin B (6), were isolated from the aerial parts of Teucrium orientale, along with four already known neoclerodane diterpenoids, teucrolivin A (1), teucrolivin B (2), teucrolivin C (3) and teucrolivin H (4), previously isolated from Teucrium oliverianum. Their structures were elucidated on the basis of spectroscopic evidence and chemical transformations. Compounds 1-3 were assayed for antifeedant activity against Spodoptera littoralis, S. frugiperda and Heliocoverpa armigera. Teucrolivin A was the most potent of the three compounds tested.
Photoinduced functionalization of diterpenes: photochemical behaviour of grandifloric acid in methanol and acetonitrile
Abstract Irradiation of grandiflorolic acid (11) at λ=254 nm in acetonitrile gave the two epimers 13 and 14 through a photodecarboxylation reaction of the carboxylic group on C-4. Irradiation of compound 11 in methanol at λ=254 nm provided the transformation of the C-20 angular methyl into a carbomethoxymethyl group. In this case, unlike compounds 13 and 14, only one of the two possible isomers (15) was obtained (equatorial methyl at C-4). A mechanistic approach of this reaction in discussed, and the role of mutual stereochemistry between C-20 methyl and C-19 carboxylic group in determining the course of the reaction is pointed out.
Scuteparvin, a new neoclerodane diterpenoid from Scutellaria parvula
Abstract The diterpenoid fraction occurring in the acetone extract of the aerial parts of Scutellaria parvula has been investigated. Only one neoclerodane diterpenoid, scuteparvin, was isolated and its structure elucidated as 4α,18-epoxy-6α- trans -cinnamoyloxy- neo clerod-13-en-15,16-olide, a new natural product. Scuteparvin is quite similar to the already known ajugarin V from Ajuga remota , the only difference being the occurrence of a trans -cinnamoyl ester system instead of an acetate on the 6α-OH group. This finding confirms that the genera Scutellaria and Ajuga are closely related taxonomically.
Photochemical reactivity of 6α-hydroxy, 7-keto neoclerodane diterpenoids
Abstract The photochemical reactivity, in methanol at λ = 254 nm, of two 6α-hydroxy-7-keto neoclerodane, isoeriocephalin ( 1 ) and teucrolivin B ( 2 ) was evaluated. From the first compound, two new products were obtained: the 6β-hydroxy epimer ( 3 ) and the ɛ-lactone ( 4 ). The second one yielded exclusively the new spiro γ-lactone ( 5 ). The formation of these new products can be explained by the well-known radical mechanism Norrish type I.