Deacylated-anti-isohumulone

Fig. 73. Structural formulae of deacylated anti-isohumulone (155), compounds 156-160, deacylated anti-acetyihumulinic acid (161) and deacylated anti-humulinic acid (162).

Fig. 73) (7). Similarly, racemic deacylated anti-isohumulone is obtained starting from synthetic deacylated humulone (158, Fig. 73) (8). Furthermore, the lower homologue 160 (Fig. 73) of deacylated anti-isohumulone has been isolated via the model compound 159 (Fig. 73) for humulone (9).

Fig. 74. Reaction scheme for the formation of the isohumulones (65,66), the anti-isohumulones (148,149) and deacylated anti-isohumulone (155) via acyloin rearrangements of humulone.

The formation of deacylated anti-acetyihumulinic acid from deacylated anti-isohumulone must proceed in an analogous way as for the formation of acetylhumulinic acids from isohumulones (see 8.3.2.). The intermediates, such as the deacylated anti-allo-isohumulones and the dehydrated derivative, have not yet been isolated. 

In addition to the anti-isohumulones, the deacylated anti-isohumulone and the corresponding derivatives, two components containing anti-structures have been isolated. The primary anti-components are transformed in the reaction medium to several classes of compounds, to which the two representatives belong. It may be deduced that many more derivatives of the anti-series exist. 

Compound 168 is clearly a derivative of deacylated anti-isohumulone (155, Fig. 73). Upon degradation of deacylated anti-acetyihumulinic acid (161, Fig. 73) 2-methylpropanal is formed (see 8.3.2. and 10.2.2.2.). An aldol condensation between these compounds, followed by dehydration, leads to formation of 168. Similar alkylidene-containing products, derived from deacylated anti-isohumulone itself, are possibly present in the complex reaction mixture, but have not yet been detected. 

In the normal isomerization of humulone (70) the bond between C-1 and C-6 is broken and a new bond is formed between C-1 and the carbonyl group at C-5 (Fig. 14.6). The reversed isomerization of humulone (Fig. 14.8), in which the bond between C-5 and C-6 is broken and the new bond formed between C-5 and the carbonyl on C-1, has now been found to occur and the unti-products account for about 10% of the isomerization mixture [93]. By boiling humulone in a buffer solution at pH 11-0 the cis- and tmn.r-isomers of both acetylhumulinic acid (88) are formed. The bitter tasting hop acids known [94]. In the mixture of isomerization mixture are deacylated anti-derivatives deacyl-ated anti-isohumulone (90), deacylated anti-acetylhumulinic acid (91), and deacylated onti-humulinic acid (92) [93]. Deacylated humulone (89) is readily isomerized to these products whereas the deacylation of anti-isohumulone only occurs to a limited extent (< 2 %) so it has been proposed [95] that (90), (91) and (92) are formed via deacylated humulone (89). However, the relative ease of deacylation of humulone and Deacylated derivatives of isohumulone have not been characterized in isomerization mixtures. 

The formation of deacyiated anti-isohumulone can be represented, either via deacylation of anti-isohumuione or via the anti-rearrangement of deacylated humulone. From treatment of cis anti-isohumulone under various pH conditions, it appears that deacylation occurs oniy to a very minor extent (< 2%). The main changes occur in the 4-methyl-3-pentenoyi group, while the 3-methylbutanoyl side chain shows poor reactivity (6). On the other hand, it has been proved that deacylated six-membered ring hop derivatives rearrange very smoothiy to compounds with anti-structure. Thus, deacylated tetrahydrohumulone (156, Fig. 73), obtained syntheticaily, is converted to racemic deacylated tetrahydro-anti-isohumulone (157,... 

The total yield of the deacylated derivatives of the anti-series is 8.5%. When the anti-isohumulones and the anti-acetyihumulinic acids are included, the yield even exceeds 10%. This is certainly not negligible in comparison with the most important hop bitter acids, the isohumulones. 

The deacylated compounds show the highest water-solubility of all anti-derivatives. As the utilization yield is consequently high, the compounds of the anti-series occur in beer (10). Since the deacylated components of the anti-series are half as bitter as the isohumulones, the contribution to the overall bitter taste of beer will not be negligible. 

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