Alkylsquarates as key intermediates for the rapid preparation of original drug-inspired compounds

Many natural privileged scaffolds contain a basic nitrogen atom, which often is a key element of pharmacophore and a chemically reactive centre as well. In our ongoing research program devoted to the design of targeted libraries based on acidic templates, we developed methods to convert privileged basic compounds -like natural alkaloids or drugs into acidic compounds. This conversion led to a profound alteration of the pharmacophore, without changing the overall shape and lipophilicity of the molecule. We expect such modifications to generate unexpected biological activities. Recently, we focused on derivatives of squaric acid, a vinylogous carboxylic acid. Two series were studied. First we describe a new, selective parallel synthesis of squaramic acids from a dissymmetric diester (3-tert-butoxy-4-ethoxy-cyclobut-3-en-1,2-dione). This efficient procedure avoids the synthesis of the undesired squaramides. Secondly we describe a microplate parallel synthesis (15 micromol-scale) of squaric acid hydroxamate amides from a squaric hydroxamate ester.