In most of the iridoids obtained from Plumeria species, a simple or branched alkyl chain of four carbons is introduced at C-10 by malonyl CoA or acetyl CoA as ketide group which is then reduced to unsaturated or saturated alkyl chain or modified to
lactonic moiety [22].
The Boehm's titration method provides qualitative and quantitative information regarding the total amount of basic groups and the amounts of acidic functional groups such as carboxylic,
lactonic, and phenolic.
The methanolic fractions enrichedin acetogenins were used to characterize
lactonic compounds according to the protocol described by Aromdee et al, (2005).
A sharp peak at 1238 [cm.sup.-1] is responsible for [delta]C-O of six-membered
lactonic ring.
Free,
lactonic and total acidities were titrated in the same solution used for pH measurement (AOAC, 1975).
The numbers of acidic sites of various types were calculated, assuming that NaHC[O.sub.3] neutralises carboxyl groups only, [Na.sub.2]C[O.sub.3] neutralises carboxyl and
lactonic groups, and NaOH neutralises all acidic groups including phenolic groups.
Applications of different forms of brassinosteroid analogues (ketonic and
lactonic spirostane) resulted in an increase of fresh weight of leaves and higher menthol production in M.
The three bases used in titration are considered as approximate probes for acidic functionalities: NaHC[O.sub.3] (carboxylic), Na2C[O.sub.3] (carboxylic and
lactonic), NaOH (carboxylic,
lactonic and phenolic).
Lactonic carbazole alkaloids from the root bark of Clausena excavata.