Novel diterpenoid acetylcholinesterase inhibitors from Salvia miltiorhiza

Acetylcholinesterase (AChE, EC 3.1.1.7) inhibitors are the only registered drugs used to treat Alzheimer's disease (AD). New AChE inhibitors may contribute to the design of new pharmaceuticals and supply information which will facilitate the understanding of the interaction between inhibitors and the enzyme. The dried root of Salvia miltiorhiza is called 'Danshen' in China, and has been used for the treatment of cerebrovascular disease and CNS deterioration in old age for over one thousand years. In this work, a modified Ellman method was used to guide the fractionation of the active AChE inhibitory compounds from an acetone extract. Four inhibitory compounds, dihydrotanshinone, cryptotanshinone, tanshinone I and tanshinone IIA were isolated, and the structures were identified by comparison of their spectral characteristics with previous reports. The inhibitory activities of dihydrotanshinone and cryptotanshinone were dose-dependent, their IC50 values being 1.0 muM and 7.0 muM, respectively. These two compounds were the major inhibitory compounds in the extract as judged by HPLC analysis, forming 0.054% w/w and 0.23% w/w in the dried root, respectively, and in mixture they appear to be less active than as isolated compounds. The clogP values of dihydrotanshinone, cryptotanshinone, tanshinone I and tanshinone IIA were calculated as 2.4, 3.4, 4.8 and 5.8, respectively, which indicate that these compounds have potential to penetrate the blood-brain barrier. This is the first example of diterpenoids as inhibitors of AChE.