Unexpected syntheses of seco-cyclopropyltetrahydroquinolines - from a radical 5-exo-trig cyclization reaction: analogs of CC-1065 and the duocarmycins

Evidence for Dual Site Binding of Nile Blue A toward DNA: Spectroscopic, Thermodynamic, and Molecular Modeling Studies

Binding of Nile Blue (NB) with calf thymus DNA has been studied using molecular modeling, spectroscopic, and thermodynamic techniques. Our study revealed that NB binds to the DNA helix by two types of modes (groove binding and intercalation) simultaneously. The thermodynamic study showed that the overall binding free energy is a combination of several negative and positive free energy changes. The binding was favored by negative enthalpy and positive entropy changes (due to the release of water from the DNA helix). The docking study validated all experimental evidence and showed that NB binds to a DNA minor groove at low concentrations and switches to intercalation mode at higher concentrations.

A versatile synthesis of "tafuramycin A": a potent anticancer and parasite attenuating agent

An improved and versatile synthesis of tafuramycin A, a potent anticancer and parasite-attenuating agent, is reported. The three major improvements that optimized yield, simplified purification and allowed the synthesis of more versatile duocarmycin analogues are: a first-time reported regioselective bromination using DMAP as catalyst; the control of the aryl radical alkene cyclization step to prevent the dechlorination side reaction; and the design of a new protection/deprotection method to avoid furan double bond reduction during the classical O-benzyl deprotection in the final step. This alternative protection/deprotection strategy provides ready access to duocarmycin seco-analogues that carry labile functionalities under reducing reaction conditions. Tafuramycin A (3) was prepared in either 8 steps from intermediate 6 or 7 steps from intermediate 17 in 52% or 37% yield respectively. Our strategy provides a significant improvement on the original procedure (11% overall yield) and greater versatility for analogue development.

Cyclization of free radicals at the C-7 position of ethyl indole-2-carboxylate derivatives: an entry to a new class of Duocarmycin Analogues

Aryl free-radicals generated at the C-7 position of ethyl indole-2-carboxylates bearing N-allyl and propargylic groups triggered intramolecular cyclizations to furnish a new class of Duocarmycin analogues, formal ethyl pyrrolo[3,2,1-ij]quinoline-2-carboxylate derivatives, through the less favorable 6-endo-trig cyclization mode.