Azadirachtin

Azadirachtin is a chemical compound belonging to the limonoids. It is a secondary metabolite present in the Neem tree seeds. The molecular formula is C35H44O16. Azadirachtin is a highly oxidised tetranortriterpenoid which boasts a plethora of oxygen functionality, comprising an enol ether, acetal, hemiacetal, and tetra-substituted oxirane as well as a variety of carboxylic esters. It is classified among the plant secondary metabolites.

Azadirachtin has a complex molecular structure, and as a result the first synthesis was not published for over 22 years after the compound's discovery. The first total synthesis was completed by Steven Ley in 2007. Both secondary and tertiary hydroxyl groups and tetrahydrofuran ether are present and the molecular structure reveals 16 stereogeneic centres, 7 of which are tetrasubstituted. These characteristics explain the great difficulty encountered when trying to produce it by a synthetic approach.

It was initially found to be active as a feeding inhibitor towards the desert locust (Schistocerca gregaria), it is now known to affect over 200 species of insect, by acting mainly as an antifeedant and growth disruptor, and as such it possesses considerable toxicity toward insects (LD50(S. littoralis): 15 ug/g). It fulfils many of the criteria needed for a natural insecticide if it is to replace synthetic compounds. Azadirachtin is biodegradable and shows very low toxicity to mammals, thus being environmentally sound.

This compound is found in the seeds of the Neem tree (0.2 to 0.8 percent by weight) or Azadirachta indica (hence the prefix aza does not imply an aza compound). Many more compounds, related to Azadirachtin, are present in the seeds as well as in the leaves and the bark of the Neem tree which also show strong biological activities.