Capsorubin oxidation

FIGURE 5.3.3B Oxidation to ketocarotenoids, capsorubin, and capsanthin. Enzyme abbreviations and enzyme activities are defined in Table 5.3.1. 

Eleven apo-carotenoids (1-11), including five new compounds, 4, 6, 9,10 and 11, were isolated from the fruits of the red paprika collected from Japan by Maoka et al. (2001b). The structures of new apocarotenoids were determined to be apo-14 -zeaxanthinal (4), apo-13-zeaxanthinone (6), apo-12 -capsorubinal (9), apo-8 -capsorubinal (10) and 9,9 -diapo-10,9 -retro-carotene-9,9 -dione (11) by spectroscopic analysis. The other six known apocarotenoids were identified to be apo-8 -zeaxanthinal (1), apo-lO -zeaxanthinal (2), apo-12 -zeaxan-thinal (3), apo-15-zeaxanthinal (5), apo-11-zeaxanthinal (7) and apo-9-zeaxanthinone (8), which had not been found previously in paprika. These apocarotenoids were assumed to be oxidative cleavage products of C40 carotenoid, such as capsanthin in paprika. 

Capsanthin (16) and capsorubin (16a), the colourants in paprika oleoresin, although not produced by commercial synthesis have been prepared in the course of carotenoid studies (ref. 58). Capsanthin has been synthesised from p-citraurin ( 3-hydroxy-p-apo-8 -carotenal ) which is available from zeaxanthin (3R, 3R )-p-carotene-3,3 -diol), by oxidation with potassium permanganate (ref. 59). 

With p-citraurin from natural sources or obtainable semi-syntheticallly by the oxidation of zeaxanthin with permanganate, the same racemic hydroxy ketone derived from (Y) afforded by Claisen condensation, capsanthin as a mixture of diastereoisomers (ref. 61). The process is shown in Scheme 19b. Both capsanthin and capsorubin have yet to be synthesised in optically active form. 

Many spices also contain carotenoids. The composition and changes in concentration of different carotenoids during the ripening process in different species of pepper were studied by use of a binary gradient of water/acetone and a C18 RP column (245-247). An isocratic RP HPLC separation of capsanthin and capsorubin in Capsicum annum paprika and oleoresin on a Merck LiChros-pher 100 C18 5-p.m (0.4 X 25 cm) column with CH3CN/2-propanol/ethyl acetate (80 10 10) has been described (248). The carotenoids in saponified extracts of irradiated and ethylene oxide-treated red pepper were determined by HPLC on... 

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