Seasonal variation of kaurane-type diterpenes and cinnamic acid derivatives in leaves of Mikania laevigata and Mikania glomerata cultivated under different shading conditions

Mikania glomerata Spreng. and Mikania laevigata Sch.Bip. ex Baker are medicinal plants popularly named 'guaco', whose leaves are used to treat respiratory diseases, with coumarin (1) and kaurane-type diterpenes regarded as the bioactive constituents. The goal of the study was to undertake seasonal studies on the contents of chemical markers in leaves under different shading conditions. Species were cultivated under different levels of solar radiation and full sunlight. The leaves were collected in the middle of each season year.The contents of 1, o-coumaric (2), benzoylgrandifloric (3), cinnamoylgrandifloric (4) and kaurenoic (5) acids were quantified in dried leaves of both species by RP-HPLC [1].Significant differences were found in the contents of cinnamic acid derivatives (1 and 2) and kaurane-type diterpenes (3, 4 and 5) for the evaluated harvesting periods and cultivation environments. o-Coumaric acid was solely detected in M. laevigata in concentrations bellow the limit of quantification (<0,045%), in plants under 80% shading, collected in the autumn. Both 1 and 2 were not detected in the analyzed samples of M. glomerata.The average concentration of coumarin reached its maximum (0.94%) in the summer, in plants growing under 80% shading.In general, both species presented higher amounts of the kaurane-type diterpenes in plants cultivated under sunlight, except for 3 in M. glomerata. Altogether, the obtained results point out that the highest content of coumarin is reached in M. laevigata cultivated under 80% shading, preferentially harvested in the summer, but with reduced levels of kaurane-type diterpenes.On the other hand, M. glomerata shall be cultivated under full sunlight for maximum contents of the kaurane-type diterpenes.

Acknowledgement: Acknowledgments: FAPEMIG, CAPES and CNPq, for the financial support.

References: 1. Bertolucci SKV et al. (2009) Planta Med 75: 280–285.