Post-Ugi Transformations for the Access to Pyrrolobenzodiazepine Scaffolds with Different Degrees of Unsaturation.

The synthesis of three novel families of pyrrolo[2,1-c][1,4]benzodiazepine-5-ones is described. The compounds were prepared according to a three-step sequence, involving an Ugi reaction, building of the pyrrolo nucleus, and reduction-cyclization to the corresponding diazepine. Depending on the amine employed in the synthesis of the Ugi adducts, different unsaturation degrees could be obtained in the pyrrolo ring (saturated or with endo or exo unsaturations), a key feature determining their biological activity, as it affects the affinity of the pyrrolobenzodiazepines toward DNA and thus their cytotoxicity. This synthetic methodology represents a significant improvement with respect to those described in the literature so far, as it uses inexpensive and commercially available starting materials without needing derivatization or the use of protecting groups.