Bodipy-Labeled Allopregnanolone: Synthesis, GABA_A Receptor Positive Allosteric Modulation, In Silico Binding Pose...

The first BODIPY-allopregnanolone conjugates have been synthesized by selecting the C21 position for labeling. The steroidal moiety and BODIPY fluorophores were coupled through flexible amino acid-derived linkers, designed with rotatable bonds and a variable carbon chain length. Сonjugates were characterized, with quantum yields of up to 79% and high extinction coefficients. All compounds showed a reasonable ability to potentiate GABA-evoked currents in isolated cerebellar Purkinje neurons. Interactions of the conjugates with the GABA_A receptor were investigated by molecular docking calculations, which predicted that the BODIPY fluorophore linked to 3α5αTHP via the C21 atom does not prevent the binding of the 3α5αTHP moiety at the neurosteroid site on the β(+)/α(-) intersubunit interfaces. Fluorescence microscopy studies demonstrated that the BODIPY-3α5αTHP III effectively stains Purkinje neurons in cerebellar slices and preferentially labels neuronal populations amidst coexisting astroglia in hippocampal tissue slices.