Gardenamide A from Rothmannia urcelliformis (Rubiaceae) - Isolation, absolute stereostructure, and biomimetic synthesis from genipine

The iridoid alkaloid gardenamide A (3) was isolated from the phytochemicall y uninvestigated East African Rubiaceae species Rothmannia urcelliformis (H iern) Bullock. Its absolute stereostructure was determined by quantum chemi cal CD calculations, which constitutes the first application of this useful chiroptical tool within the class of iridoids. An additional stereochemica l proof succeeded by its biomimetic partial synthesis starting from the wel l-known nitrogen-free iridoid genipine (1).