Lupinine - the chemical stopping you from eating Lupin

Lupinine ([1R-trans]-Octahydro-2H-quinolizine-1-methanol) (CAS: 10248-30-3) is a chemical that classified in Quinolizidine alkaloid group. Lupinine contains hydroxyethyl substituent in an axial position of Quinolizidine ring system (2 heterocyclic ring containing-nitrogen).

Structure of Lupinine. Click image for 3D structure

Lupinine is synthesized when the lysine is CO₂ reduced by coenzyme pyridoxal 5'-phosphate activity. The pathway is divided in two directions: the subway synthesizes Lupinine by two reductive steps, and the main synthesis stream goes via the Schiff-base formation and coupling to the compound substrate.

Lupinine and other alkaloids give a bitter tasting for Lupinus species (lupins), plants of the family Fabaceae. Lupin with bitter taste are unsuitable for human and animal consumption because of high alkaloids content.

The mean total alkaloid content of sweet lupin seed is approximately 130 – 150 mg kg^–1, but bitter seeds contain approximately four times that amount, overall the alkaloid content is affected by geography and climate. Some countries (Australia, France, Great Britain and New Zealand) have imposed limits on the Quinolizidine alkaloid content of seed or flour, typically at 200 mg kg^–1.

Lupin alkaloids are acutely toxic to humans. Quinolizidine alkaloid poisoning causes trembling, shaking, excitation, and convulsion. Lupinine shows a moderate toxicity invertebrates. The lethal dose of lupanine tested to be approximately 100 mg kg^–1 of lupin seeds. In Lupin seeds, Quinolizidine alkaloid content is substantially destroyed by cooking, when the cooking procedure is insufficient, 10 g of seeds may liberate more than 100 mg of lupinine.

SMILES: C1CCN2CCC[C@H]([C@H]2C1)CO

References:

• Tadeusz Aniszewski, Chapter 2 - Alkaloid chemistry, In Alkaloids (Second Edition), Elsevier, Boston, 2015, Pages 99-193, ISBN 9780444594334, https://doi.org/10.1016/B978-0-444-59433-4.00002-X.
• C. Crews, Natural Toxicants: Alkaloids, In Encyclopedia of Food Safety, edited by Yasmine Motarjemi,, Academic Press, Waltham, 2014, Pages 251-260, ISBN 9780123786135, https://doi.org/10.1016/B978-0-12-378612-8.00175-X.
• Paolo A., Patrizia M., Anna A.i, and Giovanna B. (2014) Quality of Lupinus albus L. (White Lupin) Seed: Extent of Genotypic and Environmental Effects. Journal of Agricultural and Food Chemistry 62 (28), 6539-6545 DOI: 10.1021/jf405615k
• Resta, D., Boschin, G., D'Agostina, A. and Arnoldi, A. (2008), Evaluation of total quinolizidine alkaloids content in lupin flours, lupin-based ingredients, and foods. Mol. Nutr. Food Res., 52: 490–495. doi:10.1002/mnfr.200700206