Andreas Hamm

Multiple convergence in polyketide biosynthesis: a third folding mode to the anthraquinone chrysophanol.

The polyketide chrysophanol is shown to be formed, in an organism-specific way, by a third folding mode, involving a remarkable cyclization of a bicyclic diketo precursor, thus establishing the first example of multiple convergence in polyketide biosynthesis.

Gardenamide A fromRothmannia urcelliformis (Rubiaceae) − Isolation, Absolute Stereostructure, and Biomimetic Synthesis from Genipine

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).

Genoketides A1 and A2, new octaketides and biosynthetic intermediates of chrysophanol produced by Streptomyces sp AK 671

The new aromatic polyketides genoketide A1, genoketide A2 and prechrysophanol glucuronide are biosynthetic intermediates of the octaketide chrysophanol. They were isolated from the alkaliphilic strain Streptomyces sp. AK 671 together with the new metabolite chrysophanol glucuronide. The structures of the compounds were elucidated by mass spectrometry and NMR methods. Genoketide A2 exhibited a slight and prechrysophanol glucuronide a more pronounced inhibition of the proliferation of L5178y lymphoma cells.