Pyrazolo[3,4-d]pyrimidines as Sirtuin Inhibitors: A Preliminary Synthetic and Biological Study

Sirtuins (SIRTs) are a family of NAD⁺-dependent deacetylases implicated in key cellular functions such as metabolism, translation, and genome stability. Seven human isoforms are known (SIRT-1 to SIRT-7), and they seem to act as oncopromoters or oncosuppressors, depending on the sirtuin and the cancer type. Their dysregulation is associated with major diseases including cancer, diabetes, and neurodegeneration. In detail, an overexpression of SIRT-2, is related to liver cancer, malignant gliomas, and melanoma, making it an attractive therapeutic target. The availability of many X-crystallographic data about SIRT-2−ligand complexes made it possible to build up a structure-based investigation in the hunt for SIRT-2 inhibitors, prompting an in silico evaluation followed by in vitro testing of a selection of compounds from our in-house library of pyrazolo-pyrimidines, to discover 26 novel SIRT-2 inhibitors. The synthesis of the two libraries of pyrazolo[3,4-d]pyrimidine derivatives 1-26 was driven by different modelling cycles. The first series features a phenyl vinyl group at the N1 position (compounds 1-13). The second one is characterized by a substituted or unsubstituted phenylethyl chain at N1 (compounds 14-26). In both libraries, all the analogues were obtained by a multistep synthesis, and various substituents were introduced at positions 4 and 6 to explore the SAR. Finally, the synthesized derivatives were tested in vitro to investigate the percentage of inhibition of SIRT-2 and the IC50 of the most active analogues.