Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 20, 2012
Publication Date: March 20, 2012
Citation: Colegate, S.M., Gardner, D.R., Joy, R.J., Betz, J.M., Panter, K.E. 2012. Dehydropyrrolizidine alkaloids, including monoesters with an unusual esterifying acid, from cultivated Crotalaria juncea (Sunn Hemp cv. 'Tropic Sun'). Journal of Agricultural and Food Chemistry. 60: 3541-50. Interpretive Summary: Cultivation of Crotalaria juncea (Sunn Hemp cv. “Tropic Sun”) is recommended as a green manure crop in a rotation cycle to improve soil condition, help control erosion, suppress weeds, and reduce soil nematodes. Because Sunn Hemp belongs to a family of plants that in species are known to contain toxic compounds known as dehydropyrrolizidine alkaloids the roots, stems, leaves and seed of cultivated Sunn Hemp were collected and analyzed for the toxins. Toxic dhydropyrrolizidine alkaloids were detected in all plants parts. Details of the identification and quantitation of the individual alkaloids is presented including the identification of two new compounds. The concentration of the toxic alkaloids in the plant material in the different plant parts was found to be 0.05, 0.12, 0.01, and 0.15% in the roots, stems, leaves and seeds respectively.
Technical Abstract: Cultivation of Crotalaria juncea L. (Sunn Hemp cv. ‘Tropic Sun’) is recommended as a green manure crop in a rotation cycle to improve soil condition, help control erosion, suppress weeds, and reduce soil nematodes. Because C. juncea belongs to a genus that is known for the production of toxic dehydropyrrolizidine alkaloids, extracts of the roots, stems, leaves, and seeds of ‘Tropic Sun’ were analyzed for their presence using HPLC ESI/MS. Qualitative analysis identified previously unknown alkaloids as major components along with the expected macrocyclic dehydropyrrolizidine alkaloid diesters, junceine and trichodesmine. The dehydropyrrolizidine alkaloids occurred mainly as the N-oxides in the roots, stems, and, to a lesser extent, leaves, but mainly as the free bases in the seeds. Comprehensive spectrometric and spectroscopic analysis enabled elucidation of the unknown alkaloids as diastereoisomers of isohemijunceine, a monoester of retronecine with an unusual necic acid. The dehydropyrrolizidine alkaloid contents of the roots, stems, and leaves of immature plants were estimated to be 0.05, 0.12, and 0.01% w/w, respectively, whereas seeds were estimated to contain 0.15% w/w.