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This article describes the adventure of the structural determination of the pyrrolizidine alkaloid monocrotaline that took over thirty years to be unraveled. This alkaloid was isolated for the first time from Crotalaria retusa, a species toxic to cattle and widely scattered in pastures worldwide. The determination of the structure of monocrotaline was carried out by degradative processes. Each product obtained from reactions were separated and purified. Their structures were confirmed by comparison with substances of known structure and stereochemistry. These comparisons were made by using physical properties. DOI: 10.5935/1984-6835.20130028Este artigo descreve a aventura dos químicos de produtos naturais, durante mais de 30 anos, para chegarem à determinação estrutural do alcaloide pirrolizidínico monocrotalina, isolado pela primeira vez de Crotalaria spectabilis, uma planta tóxica para bovinos, largamente espalhada pelas pastagens de todo mundo. A determinação da estrutura da monocrotalina foi feita através de reações de degradação, e cada um dos pedaços obtidos a partir dessas reações tiveram suas estruturas comparadas, através de constantes físicas, com substâncias de estruturas e configurações absolutas conhecidas. DOI: 10.5935/1984-6835.2013002

Structural Determination of the Pyrrolizidine Alkaloid Monocrotaline: An Example of the Challenges of the Natural Products Chemistry Until the 1960's