Synthesis, Biological Evaluation and Molecular Docking of Avicequinone C Analogues as Potential Steroid 5 alpha-Reductase Inhibitors

Avicequinone C (5a), a furanonaphthoquinone isolated from the Thai mangrove Avicennia marina has been shown previously to have interesting steroid 5 alpha-reductase type 1 inhibitory activity. In this study, a series of avicequinone C analogues containing furanonaphthoquinone with different degrees of saturation and substituents at the furan ring were synthesized. The resulting synthetic avicequinone C and analogues (5a-f) along with some related compounds including 2,5-dihydroxy-1,4-benzoquinone (6) and natural naphthoquinones such as lawsone (7a) and lapachol (7b) were evaluated for their in vitro cell viability and steroid 5a-reductase type 1 inhibitory activities using the cultured cell line of human keratinocytes (HaCaT). This cell-based bioassay was performed based on a direct detection of the enzymatic product dihydrotestosterone (2) by using a non-radioactive high performance thin layer chromatography (HPTLC) method. Among the furanonaphthoquinones in this series, 5e having a propionic substituent at furan ring possessed approximately 22-fold more potent than the original isolated compound 5a. However, the compounds without furan motif such as 6, 7a and b could not inhibit the activity of steroid 5 alpha-reductase. Molecular docking results of the in silico three-dimensional steroid 5a-reductase type 1-reduced nicotinamide adenine dinucleotide phosphate (NADPH) binary complex was performed via AutoDock Vina and it illustrated that the furanonaphthoquinone moiety and the substituent at furan ring might play a key role as pharmacophores for the steroid 5 alpha-reductase inhibitory activity.