Grasshopper ketone

Scheme 18.13 Synthesis of the grasshopper ketone (34) according to Eugster and co-workers [46d] (DIBAH = diisobutylaluminum hydride).

Scheme 18.14 Naturally occurring glycosides ofthe grasshopper ketone-...

The defensive excretion of the grasshopper Romalea microptera contains the allenic ketone (10). This structure is clearly related to neoxanthin (57). Racemic samples of (10) were synthesised by two routes (Scheme 5) and, although there were some differences between the two products, their n.m.r. spectra show that they belong to the natural series and that they are clearly different from the photochemically synthesised isomer (3-OH, 90, R = Ac). The stereochemistry of the synthetic racemate was shown by X-ray crystallography to be the same as an optically active sample derived from the degradation of fucoxanthin. The absolute stereochemistry of the latter sample presumably also applies to the grasshopper ketone itself. 

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).

Other functions of carotenoids are briefly mentioned here. These include phototropism and phototaxis, reproduction, camouflage colour, precursor role of neoxanthin (38, Fig. 16) for the plant growth hormone abscisic acid and the ant repellent grasshopper ketone [18,41], and cell-cell communication [49], In recent years the function of zeaxanthin (15) and lutein (25) in the human retina has received much attention, cf. the section on Health aspects. 

A representative allenic carotenoid is mimulaxanthin (202), a symmetrical structure with allenic end groups. For the total synthesis of mimulaxanthin (202), the most suitable candidate starting compound is the grasshopper ketone (11a) which has been synthesized by several groups [7-13]. 

Of all Ci3-norisoprenoids, P-damascenone and P-ionone, smelling like honey and violets respectively, have the lowest odor threshold values (Table 3.59). Precursor of P-damascenone is neoxanthine, out of which the Grasshopper ketone (I in Formula 3.142) is formed by oxi-... 

Besides the Grasshopper ketone, another enin-diol (Formula 3.141) was identified in grape juices. When heated (pH 3), this enindiol yields 3-hydroxy- P-damascone as main and P-damascenone as minor product. 

The special ketone known as grasshopper ketone arises from (3S,5 R,6 R,3 S,5 R,6 J )-5 6 -epoxy-6,7-didehydro-5,6,5, 6 -tetra-hydro-P,(5-carotene-3,5,3 -triol (neoxanthin). While maintaining... 

J,65)-5,6-epoxy-3-hydroxy-P-ionone (35,5/ ,6/ )-grasshopper ketone 9-196, fission products of alicycUc carotenes and xanthophylls... 

P-D-glucopyranoside of grasshopper ketone Figure 9.27 Formation of p-damascenone from grasshopper ketone. 

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