Technische Verfahren zur Synthese von Carotinoiden und verwandten Verbindungen aus 6‐Oxo‐isophoron. II. Ein neues Konzept für die Synthese von (3RS, 3′RS)‐Astaxanthin

Abstract

SummaryStarting from 6-0x0-isophorone (2) a new concept for a seven-step synthesis of (3RS,3'RS)-astaxanthin (1) has been developed. As a key feature of the new approach, the oxidation state of astaxanthin (1) is adjusted already at an early stage of the synthesis. Thus, manipulation on more complex intermediates later in the synthesis is reduced to a minimum. Acetonide 10 or dimer 13 represent the key intermediates of this concept (Scheme 2). The whole sequence has been run on a kg scale with an overall yield of 52% (s. Scheme 5).1. Einleitung. -Kurzlich berichteten wir [l] iiber die Modifizierung einer von Kienzle & Muyer [2] beschriebenen Synthese von (3S, 3's)-Astaxanthin (la) zu einem effizienten, technisch anwendbaren Verfahren. Daran unbefriedigend geblieben war die durch den prinzipiellen Syntheseplan bedingte, relativ hohe Stufenzahl (14). Wir beschreiben nun ein vollig neues Synthesekonzept, welches ebenfalls ausgehend von 6-0x0-isophoron3) (= 3,5,5-Trimethyl-2-cyclohexen-1,4-dion; 2) in nur 7 Stufen und in der hohen Gesamtausbeute von >50% zum (3RS,3'RS)-Astaxanthin (1) fuhrt.

Free Radical Scavenging and Cellular Antioxidant Properties of Astaxanthin

“…Most astaxanthin used in aquaculture nutrition is produced synthetically which yields three different stereoisomers, including 3S , 3′S ; 3R , 3′S ; and 3R , 3′R [ 1 ]. In 1981, Widmer et al [ 6 ] synthesized astaxanthin from the educt 6- oxo -isophorone (3,5,5-trimethyl-2-cyclohexene-1,4-dione) via a seven-step synthesis. Over a Wittig reaction of two equivalents C15-phosphonium salt with C10-dialdehyde, astaxanthin was obtained with yields up to 50% yields [ 6 ].…”

“…In 1981, Widmer et al [ 6 ] synthesized astaxanthin from the educt 6- oxo -isophorone (3,5,5-trimethyl-2-cyclohexene-1,4-dione) via a seven-step synthesis. Over a Wittig reaction of two equivalents C15-phosphonium salt with C10-dialdehyde, astaxanthin was obtained with yields up to 50% yields [ 6 ].…”

Recent advances in industrial carotenoid synthesis

“…• epoxidation of the C-C double bond to yield 18 • rearrangement of the epoxide to the sodium enolate 19 of the corresponding tricarbonyl compound • catalytic hydrogenation of the reactive carbonyl group to 20 • fixing and protection of the enolized α-hydroxyketone group as a dioxolane Here the process described by Hoffmann-LaRoche proceeds via a five-membered ketal ring 21 [7] while BASF decided in favor of a five-membered acetal ring 22 produced by twofold acid-catalyzed addition of the diol to a vinyl ether (Fig. 4) [8].…”

“…These are ß-apo-8′-carotenal (6), ethyl ß-apo-8′-carotenoate (7), and citranaxanthin (8). The aldehyde is used as a food colorant while the ester and the ketone are employed as animal feed additives in poultry farming (Fig.…”

Recent Advances in Industrial Carotenoid Synthesis

“…In addition to these C 40 -carotenoids, three apocarotenoids are manufactured on an industrial scale. These are ß-apo-8′-carotenal (6), ethyl ß-apo-8′-carotenoate (7), and citranaxanthin (8). The aldehyde is used as a food colorant while the ester and the ketone are employed as animal feed additives in poultry farming (Fig.…”