Synthesis and biological activities of vitamin D-like inhibitors of CYP24 hydroxylase

[Display omitted] ► Potent vitamin D-like CYP24 inhibitors are efficiently prepared in convergent syntheses. ► The 25- N-cyclopropylamine side chain modified vitamin D analog 3 selectively inhibits CYP24A1. ► 3 Causes differentiation of leukemia cells nearly as well as the natural hormone. ► The calcemic activity of 3 is considerably lower than that of the native hormone. ► Docking studies provide insights to the selectivity of 3 for CYP24A1 over CYP27B1. Selective inhibitors of CYP24A1 represent an important synthetic target in a search for novel vitamin D compounds of therapeutic value. In the present work, we show the synthesis and biological properties of two novel side chain modified 2-methylene-19-nor-1,25(OH) 2D 3 analogs, the 22-imidazole-1-yl derivative 2 (VIMI) and the 25- N-cyclopropylamine compound 3 (CPA1), which were efficiently prepared in convergent syntheses utilizing the Lythgoe type Horner–Wittig olefination reaction. When tested in a cell-free assay, both compounds were found to be potent competitive inhibitors of CYP24A1, with the cyclopropylamine analog 3 exhibiting an 80–1 selective inhibition of CYP24A1 over CYP27B1. Addition of 3 to a mouse osteoblast culture sustained the level of 1,25(OH) 2D 3, further demonstrating its effectiveness in CYP24A1 inhibition. Importantly, the in vitro effects on human promyeloid leukemia (HL-60) cell differentiation by 3 were nearly identical to those of 1,25(OH) 2D 3 and in vivo the compound showed low calcemic activity. Finally, the results of preliminary theoretical studies provide useful insights to rationalize the ability of analog 3 to selectively inhibit the cytochrome P450 isoform CYP24A1.