Bromocriptine Impurity A (Mixture of Diastereomers)

(6aR,9R)-5-bromo-N-((2R,5S)-5-isobutyl-2-isopropyl-3,6-dioxo-3,5,6,8,9,10-hexahydro-2H-oxazolo[3,2-a]pyrrolo[2,1-c]pyrazin-2-yl)-7-methyl-4,6,6a,7,8,9-hexahydroindolo[4,3-fg]quinoline-9-carboxamide