Isolation and degradation of triterpenoids from tissue cultures and seeds of Neem (Azadirachta indica).
A new method has been developed for the rapid separation, purification and
identification of triterpenoids from the seeds of the Neem tree (Azadirachta indica) and
cell tissue cultures from it.
The formation of triterpenoids in tissue culture was studied in collaboration with
researchers at ENEA, Rome. Tissue culture samples prepared by them have been analysed
for triterpenoids, in particular the natural insecticidal compound azadirachtin. A solid
phase extraction method was developed for the partial purification of compounds from
small quantities of tissue culture cells. Compounds were quantified using supercritical
fluid chromatography. Azadirachtin was isolated from the tissue cultures of the plant for
the first time, along with the related triterpenoids 3-acetyl-l-tigloylmeliacarpin, 3-tigloylazadirachtol
The decomposition of azadirachtin in solution at different conditions of pH and
temperature was studied. The compound was most stable in mildly acidic aqueous
conditions but readily decomposed in basic solutions. Azadirachtin decomposed more
rapidly when heated in aqueous rather than in organic solutions. At room temperature, it
was stable in organic solvents over a9 month period. At 90 °C in methanol, azadirachtin
was quantitatively converted to 3-acetyl-l-tigloyl-azadirachtinin and 3-tigloylazadirachtol
was converted to 11-dehydroxy-3-tigloylazadirachtinin.
Methods were found to reduce the reaction time and increase the yield of
salanninolide, isosalanninolide, nimbinolide and isonimbinolide, photo-oxidation products
from salannin and nimbin. Isosalanninolide, a photo-oxidised product of salannin, was
isolated from the seeds for the first time. This and other products were submitted for insecticidal tests. Studies with synthetic model compounds were made, in an attempt to
understand the nature of the photo-oxidation reactions.