Igor V. Magedov

A variant structural skeleton of epipodophyllotoxin was synthesized and found to rival the natural cyclolignan in antiproliferative and microtubule destabilizing properties. This discovery leads to a new structural class of tubulin targeting agents.

Multicomponent reactions are emerging as a powerful tool in alkaloid-based drug discovery. This highlight describes several recent (all published in 2011) examples of the employment of multicomponent reactions for the synthesis of biologically active alkaloids and their medicinally relevant analogs.

Structural simplification of an antimitotic natural product podophyllotoxin with mimetic heterocyclic scaffolds constructed using multicomponent reactions led to the identification of compounds exhibiting low nanomolar antiproliferative and apoptosis-inducing properties. The most potent compounds were found in the dihydropyridopyrazole, dihydropyridonaphthalene, dihydropyridoindole, and dihydropyridopyrimidine scaffold series. Biochemical mechanistic studies performed with dihydropyridopyrazole compounds showed that these heterocycles inhibit in vitro tubulin polymerization and disrupt the formation of mitotic spindles in dividing cells at low nanomolar concentrations, in a manner similar to podophyllotoxin itself. Separation of a racemic dihydropyridonaphthalene into individual enantiomers demonstrated that only the optical antipode matching the absolute configuration of podophyllotoxin possessed potent anticancer activity. Computer modeling, performed using the podophyllotoxin binding site on β-tubulin, provided a theoretical understanding of these successful experimental findings.

After the initial discovery of antiproliferative and apoptosis-inducing properties of a camptothecin-inspired pentacycle based on a 1H-indeno[2′,1′:5,6]dihydropyrido[2,3-d]pyrimidine scaffold, a library of its analogues as well as their oxidized planar counterparts were prepared utilizing a practical multicomponent synthetic protocol. The synthesized compounds exhibited submicromolar to low micromolar antiproliferative potencies toward a panel of human cancer cell lines. Biochemical experiments are consistent with the dihydropyridine library members undergoing intracellular oxidation to the corresponding planar pyridines, which then inhibit topoisomerase II activity, leading to inhibition of proliferation and cell death. Because of facile synthetic preparation and promising antitopoisomerase activity, both the dihydropyridine and planar pyridine-based compounds represent a convenient starting point for anticancer drug discovery.

Privileged medicinal scaffolds based on the structures of tetra- and pentasubstituted 2-aminopyrroles were prepared via one-pot multicomponent reactions of structurally diverse aldehydes and N-(aryl-, hetaryl-, alkylsulfonamido)acetophenones with activated methylene compounds. This methodology was used in a four-step synthesis of alkaloids rigidins A, B, C, and D in overall yields of 61%, 58%, 60%, and 53%, respectively. Of these, rigidins B, C, and D were synthesized for the first time.