Borylated Five-Membered Ring Iminosugars: Synthesis, Spectroscopic Analysis, and Biological Evaluation for Glycosidase Inhibition and Anticancer Properties for Application in Boron Neutron Capture Therapy (BNCT)—Part 1

<b>Background/Objectives</b>: This article reports pyrrolidine iminosugars of L-gulose absolute stereochemical configuration that are functionalised via <i>N</i>-alkylation to bear boronate ester and boronic acid pharmacophores. Inclusion of boron pharmacophores has been shown to reduce toxicity profiles of drugs and can expand the range of interactions between drugs and target enzymes. <b>Methods:</b> The synthetic development, detailed spectroscopic analysis, and biological investigation against glycosidase enzymes and cancer cell lines of these novel five-membered ring iminosugars are reported. <b>Results:</b> This family of iminosugars displays selective, moderate-to-weak inhibition (IC₅₀s = 133-501 μM) of β-d-galactosidase (bovine liver) and emerging inhibition of β-d-glucosidases (almond) and (bovine liver). The boronic acid pharmacophore may be suitable for the management of lysosomal storage disorders to support the restoration of biological activity of mutant enzymes via the chaperone-mediated therapy approach. From a structure-activity perspective, the cancer screening revealed slight growth inhibition in a panel of cancer cell lines, with A2780 ovarian carcinoma cells showing the strongest response across all compounds. Beyond the growth inhibition capabilities, the real therapeutic potential of these borylated drugs lies in their switch-on/switch-off activation under BNCT radiotherapeutic conditions. <b>Conclusions:</b> This is an important novel family of drug leads capable of interacting with drug targets via intermolecular and intramolecular interactions, changing shape and electronics. Introduction of organic boron atoms to organic molecules presents significant synthetic and purification challenges, as well as analysis of the equilibria that arise in aqueous systems. We provide a methodology to achieve all this and introduce boron pharmacophores onto carbohydrate scaffolds in a systematic manner to facilitate a more widespread adoption of boron pharmacophores.