Mimulaxanthin, Hauptcarotinoid von Lamium montanum , und seine absolute Konfiguration; konfigurative Verknüpfung von Deepoxyneoxanthin mit Neoxanthin

Mimulaxanthin, the Main Carotenoid in Lamium montanum , Determination of its Absolute Configuration. Absolute Configuration of Deepoxyneoxanthin by its Correlation with Neoxanthin The carotenoid mixture isolated from the yellow flowers of Lamium montanum P ERS. ( Labiatae ) consists of more than 75% of carotenoids with allenic end groups. Besides 32% of neoxanthin/neochrome we isolated 44% of mimulaxanthin ( 1a ), a very rare carotenoid so far only found in Mimulus sp. (Scrophulariaceae) . Its absolute configuration was determined by oxidative degradation to the known ketone 3 (‘grasshopper ketone’) and by spectroscopic and chiroptical comparisons with neoxanthin (6). Mimulaxanthin (1a) therefore is (3 S , 5 R , 6 R , 3′ S , 5′ R , 6′ R )‐6,7,6′,7′‐tetradehydro‐5,6,5′,6′‐tetrahydro‐β, β‐carotene‐3,5,3′,5′‐tetraol. Deep‐oxyneoxanthin, which was reisolated from Mimulus sp . is (3 S , 5 R , 6 R , 3′ R )‐6,7‐didehydro‐6,7‐dihydro‐β, β‐carotene‐3,5,3′‐triol (2) , as shown by spectroscopic and chemical correlation with neoxanthin ( 6; de‐epoxydation by BuLi/FeCl 3 ).