5.6- Epoxy-13 -ionone

Modern instrumentation has helped with the identification of many ionones, dehydroionones, ionols and epoxy ionones isolated from naturally occuring substances. The strong floral odor which upon dilution resembles violets occompanies a-ionone and ( ) cis-a-ionone. Either optically active isomer of ionone in the pure form provides a stronger and more pleasing odor than the racemic mixture (6). 

By similar reactions, other carotenoids give rise to ionone, linalool and substituted hydroxy- and epoxy-ionones [63]. 

Hydroxy ionones and epoxy ionones arise by hssion of various xanthophylls. For example, (S)-3-hydroxy-P-ionone arises from P-cryptoxanthin, (3 R,3 J )-p,p-carotene-3,3 diol (zeaxanthin) and 3R, 3J, 6 J )-P,8-carotene-3,3 diol (lutein). 5,6-Epoxy- -ionone arises, for example, from (3J ,5S,6S,3 J )-5,6-epoxy-5,6-dihydro-P,P-carotene-3,3 -diol (antheraxanthin) and (3S,5R,6S,3 S,5 R,6 S)-5,6,5, 6 -diepoxy-5,6,5 6 -tetrahydro-P,p-caroten-3,3 -diol (vio-laxanthin). (3 R,6 R)-3-Hydroxy-a-ionone may arise from lutein, (3S,6S)-3-hydroxy-a-ionone from (3S,3 S,6S,6 S)-8,8-carotene-3,3 -diol (lactucaxanthin) and (3S,6 R)-3-hydroxy-a-ionone from (3J ,3S, 6 J )-P,s-carotene-3,3 -diol (3 -epilutein). 

Aleu, J. Brenna, E. Fuganti, C. Serra, S. Lipase-mediated synthesis of the enantiomeric forms of 4,5-epoxy-4,5-dihydro-a-ionone and 5,6-epoxy-5,6-dihydro-/ -ionone. A new direct access to enantiopure (R)- and (S)-a-ionone. 

Among the other reported volatile TDP of B-carotene include B-cyclo-cltral, 5,6-epoxy-B-ionone and dihydroactinidiolide (25). These compounds were also found by Isoe et al. (30, 31), Wahlberg et al. (32) and Kawakami and Yamanishi (33) as photo-oxygenation products of B-carotene. Volatile thermal degradation of carotenoids has been extensively studied, mainly in nonfood systems. Hence, the objective of this study was to identify the volatile components of the TDP of B-carotene formed in a food model system. 

Thus, oxygen attack at the terminal 5,6-double bond position, followed by the formation of a peroxy epoxide and cleavage of the C-C and 0-0 bonds, resulted in 5,6-epoxy-B-ionone, while rearrangement of the 5,6-epoxy derivative, followed by reduction and oxidation, resulted in the formation of dihydroactinidiolide. Furthermore, a peroxy derivative was formed and cleaved to form 8-ionone, which then led to the formation of dihydroactinidiolide as a secondary oxidation product. 

Ten volatile compounds were produced from the pyrolysis of 6-carotene. Among them, toluene, xylene, IJ-cyclocitral, ionene, B-ionone, 5,6-epoxy-B-ionone and dihydroactinidiolide were identified. The addition of catechin gallates reduced the quantity of the ten... 

In another study, 13-carotene was heated in aqueous medium at 90°C, 120°C and 150°C. More than 40 different compounds were found in the ether extracts by GC-MS as shown in Figure 3. Dihydroactinidiolide (sweet peachy aroma) was found in highest concentration at all temperatures studied. At 90°C, 5-6-epoxy-6-ionone (sweet, violet-like) was found in second highest quantity, while at 150°C, 2,6,6-trimethyl-2-hydroxy-cyclohexanone (green, citrusy) and 2,6,6-trimethyl-2-hydroxy-cyclohexan-1-aldehyde (floral, geraniol-like) were found in large quantity. At 120°C, these compounds were more evenly balanced than at 90°C or 150°C. A balance of ionone related compounds seem to contribute to an attractive green tea flavor. 

Takazawa O, Tamura H, Kogami K, Hayashi K (1982) New Synthesis of Megastigma-4,6,8-trien-3-ones, 3-Hydroxyionol, 3-Hydroxy-6-ionone, 5,6-Epoxy-3-hydroxy-6-ionol and 3-Oxo-a-ionol. Bull Chem Soc Jap 55 1907... 

The photochemistry of a number of ionone-like compounds, including the epoxy compounds (180)—(184),the keto-acid (185),and the ( )- and (Z)-isomers of ( )-y-monocyclofarnesol (186) has been investigated intensively. In most cases a large number of products were produced. 

Epoxy-P-ionone had been reported previously by Viani et al.,(13), Schreler et al., (J 4) and V/obben et al., ( ). In the present study besides the mass spectrum an infrared absorption spectrum was also obtained and was found to be identical to that of an authentic sample. An odor threshold was determined in water solution to be 100 ppb. It is, therefore, a relatively weak odorant and as its concentration, in all fresh tomato samples examined, is well below this figure it seems unlikely that it can contribute to fresh tomato aroma. 

In a-ionone, peroxybenzoic acid and peroxyphthalic acid epoxidize solely the endocyclic double bond to give 3,4-epoxy-a-ionone in 96.5 and 66% yields, respectively [299]. Alkaline hydrogen peroxide, on the other hand, epoxidizes only the double bond conjugated with carbonyl to give a 28-31% yield of a-ionone-ot, p -epoxide [332] (equation 440). 

The conversion of frans-retinyl acetate into retinoic acid in hamster organ culture,262 and of cis- and trans-rzimoxc acid into the 5,6-epoxy- and 4-oxo-derivatives and their glucuronides has been demonstrated.263 264 Strains of Aspergillus niger metabolize ionones and related compounds to oxygenated derivatives, some of which may be useful intermediates for carotenoid synthesis. The asymmetric oxidation of p-ionone to (25, 6/ ,7/ )-2,7-epoxydihydro-a-ionone (218) has been demonstrated.265 (i )-4-Hydroxy-p-ionone (219 X = OH)... 

The ionone series of compounds has been fruitful for Jeger smd his coworkers. The area is clearly not exhausted and they have studied the behaviour of the epoxy dienes (93) under acetone-sensitized irradiation. Irradiation of the enol benzoate (94) in the presence of acid yields the isoquinolinone (95) in good yield by a mechanism involving cyclization, elimination and oxidation. ... 

Fig. 2 Structures of primary cleavage products of common carotenoids (6-ionone 1, a-ionone 2, 3-hydroxy-6-ionone 3, 3-hydroxy-a-ionone 4, 3-hy-droxy-5,6-epoxy-6-ionone 5, and grasshopper ketone 6).

Several papers have described the synthesis of epoxyretinoids. The 5,6-epoxides of fmns-retinal (88) and its (9Z)-, (IIZ)-, and (13Z)-isomers were prepared by direct epoxidation of retinal with w-chloroperbenzoic acid. The 7,8-epoxides (89) of retinal, retinol, and retinoic acid and its methyl esters were synthesized from the jS-ionone epoxide (90). The exceedingly labile methyl 13,14-epoxy-13,14-dihydroretinoate (91) was made by addition of the epoxyaldehyde (92) to the phosphorane (93). Chromogen 574 , a product of the epoxidation of retinol first described in 1945, has now been identified as the... 

Conditions for the catalytic hydrogenation of -ionone (159) to dihydro and tetrahydro products have been investigated.The autoxidation of a-, /3-, and y-ionones and their dehydro-derivatives in aprotic solvents has been studied.Products included epoxy-, oxo-, and hydroxy-derivatives. Mechanistic studies of /3-ionone oxidation have been reported. ... 

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