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