Nuclear magnetic resonance analysis of carotenoids from the burgundy plumage of the Pompadour Cotinga (Xipholena punicea)

• The plumage of Xipholena punicea contains six novel carotenoid structures.
• COSY, NOESY and 1H NMR are used to confirm the structures of the six carotenoids.
• Chemical shift data of novel substituted carotenoid ring structures is reported.

Previous analysis of carotenoids extracted from the burgundy plumage of the Pompadour Cotinga (Xipholena punicea) revealed six novel keto-carotenoid pigments with methoxyl groups in the C3-position of one or both β-rings. High performance liquid chromatography (HPLC), mass spectrometry, chemical analysis and, in some instances 1H NMR spectroscopy were employed to determine the structures of the molecules. Further analysis by NMR was precluded due to lack of material. The recent acquisition of multiple feathers from X. punicea specimens has made it possible to complete this work using correlated homonuclear spectroscopy (COSY), nuclear overhauser effect spectroscopy (NOESY) and 1H NMR. These new data conclusively confirm the structures of the six methoxy-carotenoids suggested by the earlier work. In addition, the resonance positions of the protons from the novel 3-methoxy-4-keto-β-ring and 2,3-didehydro-3-methoxy-4-keto-β-ring moieties are reported here for the first time.