Antimalarial alkaloids from a Bhutanese traditional medicinal plant Corydalis dubia Phurpa Wangchuk a,b , Paul A. Keller a , Stephen G. Pyne a,n , Anthony C. Willis c , Sumalee Kamchonwongpaisan d a School of Chemistry, University of Wollongong, Wollongong, NSW 2522, Australia b Pharmaceutical and Research Unit, Ministry of Health, Thimphu, Bhutan c Research School of Chemistry, The Australian National University, Canberra A.C.T. 0200, Australia d Medical Molecular Biology Research Unit, National Center for Genetic Engineering and Biotechnology, National Science and Technology Development Agency, Thailand Science Park, Pathumthani 12120, Thailand article info Article history: Received 11 April 2012 Received in revised form 7 May 2012 Accepted 12 June 2012 Available online 14 July 2012 Keywords: Bhutanese traditional medicine Medicinal plant Corydalis dubia Antimalarial Scoulerine abstract Ethnopharmacological relevance: Corydalis dubia is used in Bhutanese traditional medicine as a febrifuge and for treating infections in the blood, liver and bile which correlate to the signs and symptoms of malarial and microbial infections. Aim of the study: To validate the ethnopharmacological uses of the plant and to discover potential new therapeutic drug leads. Materials and methods: C. dubia was collected from Bhutan and the alkaloids were obtained using acid–base fractionation and separation by repeated column and preparative plate chromatography. The alkaloids were identified from analysis of their physiochemical and spectroscopic data and were tested for antiplasmodial, antimicrobial and cytotoxicity activities. Results: A systematic extraction and isolation protocol yielded one new natural product, dubiamine, and seven known isoquinoline alkaloids, scoulerine, cheilanthifoline, protopine, capnoidine, bicuculline, corydecumbine and hydrastine. Among the four alkaloids tested, scoulerine showed the best antiplasmodial activity with IC 50 values of 5.4 mM and 3.1 mM against the antifolate sensitive and the multidrug resistant P. falciparum strains: TM4/8.2 and K1CB1, respectively. None of the alkaloids tested showed significant antimicrobial or cytotoxicity activities. Conclusions: The antiplasmodial test results, of the isolated alkaloid components, are commensurated with the ethnopharmacological uses of this plant. & 2012 Elsevier Ireland Ltd. All rights reserved. 1. Introduction C. dubia Prain (Fumariaceae), which is locally known as Re-skon, is an annual yellow-flowering glabrous herb of lower stature arising from tuberous rootstock. This plant is endemic to Bhutan, Sikkim (India) and Chumbi Valley of Tibet (Grierson and Long, 1984). In Bhutan, it occurs in the wild in localized parts of Lingzhi and Bumthang region at an altitude range of 4294– 5039 m above sea level (Wangchuk et al., 2008; Anonymous, 2008). It grows sparsely with recorded density of 0.6–3.6 plants/ m 2 (Anonymous, 2008). Therapeutic uses of this plant were reported for detoxifying impure blood, treating fever arising from the infections of liver, heart, lung, pancreas and kidney and alleviating neuralgia and complicated disorders that have resulted from a combination of defective air, bile and phlegm (Wangchuk et al., 2011). These are symptoms which correlate to both malarial and microbial infections. A preliminary phytochemical screening demonstrated the presence of alkaloids and that the crude MeOH and CHCl 3 alkaloid extracts showed significant antiplasmodial activity against chloroquine and antifolate resistant Plasmodium falciparum strains: TM4/8.2 and K1CB1 (Wangchuk et al., 2011). This prompted us to investigate the alkaloid constituents of C. dubia with a view to generate potential new therapeutic agents and at the same time validate the use of this plant in Bhutanese traditional medicine (BTM) for the treatment of malarial or microbial infections. A systematic extraction and isolation protocol yielded one new natural product which we named as dubiamine (1) drawn from the species name of the plant. Seven known isoquinoline alkaloids were also isolated which were identified as scoulerine (2), cheilanthifoline (3), protopine (4), capnoidine (5), bicuculline (6), corydecumbine (7) and hydrastine (8). Compounds 1, 2, 5 Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/jep Journal of Ethnopharmacology 0378-8741/$ - see front matter & 2012 Elsevier Ireland Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jep.2012.06.037 n Corresponding author. Tel.: þ61 2 4221 4388; fax: þ61 2 4221 4287. E-mail address: spyne@uow.edu.au (S.G. Pyne). Journal of Ethnopharmacology 143 (2012) 310–313