Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Humulinic acids

P James, T Tynan, I McMurrough, J Byrne. Preparation, purification and separation by high performance liquid chromatography of humulinic acids, dehydrohumulinic acids, and hulupones. J Inst Brew 96 137-141, 1990. [Pg.774]

The structures assigned to isohumulone (71), humulinic acid (73), and 4-acetylhumulinic acid (74) each contain two chiral centres and should exist as two pairs of enantiomers. Since natural (R) (—)-humulone is a single enantiomer only two diastereoisomeric forms are found these are the cis and... [Pg.100]

Humulinic acids. These consist of cis and trans forms of humulinic, co-humulinic, and adhumulinic acids. [Pg.101]

Xrdens-Humulinic acid. Has empirical formula Q5H22O4 with m.p. 95 C and the lower partition coefficent in a phase system of a hydrocarbon and a buffer. Trans means the 3-methyl-2-butenyl side-chain and the alcoholic ring hydroxyl group are on opposite sides of the ring. [Pg.101]

The structures assigned to the two forms of isohumulone followed from earlier studies on humulinic acid. A second isomer of humulinic acid, m.p. 68 C, cw-humulinic acid, was isolated by countercurrent distribution of... [Pg.102]

Treatment of cw-humulinic acid with alkali caused it to revert to the trans form the equilibrium mixture consists of over 90% of rra/i -humulinic acid. Oxidation of n>humulinic acid with bismuth oxide also gave dehydrohumulinic acid [79]. This result suggested that the two humulinic acids were epimeric at C-4 and this was confirmed by proton magnetic resonance spectroscopy [79]. Thus in rr AW-humulinic acid (77 or 80 R = H) the C-4 hydroxy group and the C-5 isopentenyl chain have the trans configuration and lie on opposite sides of the planar cyclopentenone ring. In cw-humulinic acid (79 or 81 R = H) both bulky substituents lie on the same side of the ring. All these compounds exist as mixtures of tautomers. [Pg.103]

These observations were readily extended to explain the occurrence of two isomeric isohumulones (80 and 81 R = CO-CHg-CH = C ( 113)2). In the proton magnetic resonance spectrum of isohumulone, the signal given by the proton at C-5 was split. This indicates that it was a mixture of 60% of the isomer (81 R = CO-CHg-CH = C(CH3)g) with cw-humulinic acid stereochemistry and 40% of the isomer (80 R = CO CHg CH = C(CH3)g) with trans-humulinic acid stereochemistry [80]. In isohumulone there are two bulky substituents at C-4 so the two isomers will have similar stabilities. The proportions of the two isomers found by proton magnetic resonance spectroscopy were in good agreement with the estimates obtained from countercurrent distribution and reversed-phase chromatography [69, 71]. [Pg.103]

The gross structure of the iso-a-acids has been substantiated by an elegant synthesis of ( )-isohumulone [81]. The product was an oil which gave an infrared spectrum identical with that of isohumulone and which on hydrolysis afforded /raw -humulinic acid. ( )-Isocohumulone and ( )-isoadhumulone were later synthesized by the same route [82]. The overall yields in these syntheses are low so that synthetic iso-a-acids are more readily available by isomerization of synthetic a-acids [83] (see Chapter 13). [Pg.104]

Further study of the isomerization of humulone into isohumulone has shown that both in 0-1 n sodium carbonate solutions (pH 10-0) and in a phosphate buffer solution (pH 9 0) some hydrolysis to humulinic acid occurs [72, 85]. In the pH range 6-5-8-0, the isomerization is catalysed by bivalent metals as Ca +, Mg +, Cd + and Mn + in particular, the Mg + catalysed isomerization of humulone affords isohumulone free of humulinic acids [86]. [Pg.104]

The products obtained by isomerizing humulone in a phosphate buffer solution (pH 9-0) for 2 hr have been analysed in detail using counter-current distribution (Table 14.13). Both cis- and rrdn.r-humulinic acids were isolated in optically active forms. The allo-iso-humulones (K =0-41) were readily separated from the isohumulones K = 0-87) but the mixture of allo-iso-humulone isomers was not resolved even after 1000 transfers. The proton magnetic resonance spectrum of the mixture, however, established the presence of (80 and 81) (R = CO CH = CH CH(CH3)2) [73, 89]. Later... [Pg.105]

The isomerization of tetrahydrohumulone (82) at pH 9 0 has also been studied to avoid complications due to the reactivity of the unsaturated side-chains of humulone. In addition to recovered tetrahydrohumulone (36 %), cis- and rrtf/w-tetrahydroisohumulone (51%), and cis and trans-dihydro-humulinic acid (2-6%), cw-tetrahydrohumulinone (83 with side-chain double bonds saturated) is isolated in 3% yield [91]. [Pg.106]

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. [Pg.108]

The estimation of iso-a-acids in wort, beer, and isomerized hop extracts is usually based on their light-absorption properties (Table 14.12). Measurements are made at 275 nm in acid solution or 255 nm in alkaline solution. Humulinic acids, which possess no bitterness, show similar light absorption to the iso-a-acids. Both a- and p-acids show appreciable absorption at the wavelengths mentioned so all these must be absent from the extract analysed. Hulupones exhibit 80-90% of the absorption of the iso-a-acids at these wavelengths but, since they are also bitter, it is often not regarded as so important to exclude them from the analysis. Beer produced by conventional wort boiling will contain only trace amounts of a-acids and humulinic acids, and iso-a-acids may be estimated directly on an isooctane extract of the beer. Worts, on the other hand, may also contain appreciable amounts of a-acids and isomerized hop extracts may contain a-acids, iso-a-acids, and humulinic acids. [Pg.111]

The isomerization of a-acids is catalysed by calcium or magnesium ions, either in methanol solution or the solid state, without the formation of humulinic acid [86]. In the latter case the calcium and/or magnesium salts of the a-acids are heated at 70°C for 20 min to effect the isomerization. The iso-a-acid salts are usually ground to a fine powder (particles < 10 [tm) which is added to conditioning tanks where a contact time of at least 24 hr is necessary to achieve 85% utilization [121]. A modification of this process involves heating stabilized hop pellets, in which the a-acids are in the form of their calcium or magnesium salts, at 80°C for 2 hr to form isomerized pellets which contain the calcium and/or magnesium salts of iso-a-acids [122]. [Pg.113]

The analysis of isomerized hop extracts is difficult as they may contain unreacted a-acids, (3-acids, and humulinic acids, in addition to the required iso-a-acids. A preliminary qualitative analysis by thin layer chromatography... [Pg.113]

The quality and intensity of the bitter taste derived from these secondary products are different. Evaluation of hops is therefore based on a determination of composition of individual a- and P-acids, rather than of the total content of bitter substances. As seen in Table 20.4, the composition varies greatly with hop origin. During the boiling of hops, humulons isomer-ize into isohumulons (cis-compounds, VII trans-compounds, VIII cf. Formula 20.2), which are more soluble and bitter than the initial compounds. The isohumulons can be further transformed into humulinic acids (IX,X), which have only about 30% of the bitterness of isohumulons. [Pg.895]

On alkaline treatment, isohumulones are transformed into (4R,Z)- and (4S, )-humulinic acids, also known as ds-humuhnic... [Pg.650]

The utilization yield with pre-isomerized extracts can be as high as 80-90%, but these data have not been substantiated by practice over long periods. Isomerization of each alpha acid gives rise to two iso-alpha acids, a cis form and a trans form. There seems to be a small difference as regards these two forms of iso-alpha acids in the intensity and the nature of the bitter taste. The ratio of these cis and trans compounds in isomerization mixtures depends on the production method. This is an extra complication which needs careful consideration. Pre-isomerization of alpha acids with alkali or in the presence of some bivalent metal-ions leads to the formation of undesirable compounds, like the allo-iso-aipha acids, acetyihumulinic acids or humulinic acids. [Pg.22]

The first attempts at structural determination of hop compounds are ascribed to Barth in 1900 (12). He concluded that humulone exhibited acidic properties in view of its ability to form salts. Schnell obtained two decomposition products by alkaline treatment valeric acid and an unsaturated oxyketo acid (13). The latter compound was described as a weak monocarboxylic acid carrying an enolic hydroxyl function (colouration with iron(lll) ions) and referred to as a pseudoacid. The empirical names, humulone and humulinic acid, for the alkaline degradation product, were coined by Schnell. [Pg.27]

In 1916 Wollmer confirmed these results and stated that humulinic acid carried an enolic group (13). It was finally Nobel Prize winner Wieland, who proposed the detailed structure 1 (Fig. 2) for humulone in 1925 (14,15). Thus humulone may be viewed as an oxidized phloroglucinol derivative, substituted by two 3-methyl-2-butenyl... [Pg.27]

To obtain simple, well-characterized derivatives, the epimeric isohumulones have been transformed into the epimeric humulinic acids (see 8.4.) and further into the epimeric dihydrodeoxohumulinic acids (cis form 72, Fig. 37 trans form 73, Fig. 37). This last transformation is achieved by hydrogenolysis of the humulinic acids (26). The yield can be increased to 80-85% by carrying out the reaction in a 20%-solution of the humulinic acids in acetic acid with 5% Adams catalyst at 55°C during 6-8 h. The optical activity is fully retained. The epimeric compounds 72 and 73 are separated by CCD in the two-phase system ether aqueous buffer pH 7.65 after 100 transfers. The cis isomer 72 has a K-value of 1.36 and a melting point of 179°C. The UV absorption... [Pg.93]

Humulinic acid (2 g 7.52 x 10 mol) is dissolved in acetic add (10 g 1.7 x 10 mol), to which 5% Adams catalyst (platinum(IV) oxide) is added. The temperature of the hydrogenation vessel is adjusted to 55°C. After hydrogenation during 6-8 h the catalyst is filtered off and the solvent is removed. Trans dihydrodeoxohumulinic add... [Pg.94]

The absolute representations of the methyl enol ethers of the dihydrode-oxohumulinic acids can directly be transmitted to those of the humulinic acids and the isohumulones (see 8.4.1.3.). Cis isohumuione 65 has the (4R,5S)-configuration, trans isohumulone 66 the (4S,5S)-configuration. [Pg.98]

Alkaline degradation of the spiro-isohumulones leads to the humulinic acids (see... [Pg.112]

Further heating causes decomposition. Consequently, the isohumulones can never be obtained in pure form by distillation because of humulone impurities. It can not be concluded whether traces of humulone, present in beer (84), are due to non-reacted humulone from hops or to conversion of the isohumulones. The ring expansion most probably follows the same stereochemical pathway as the ring contraction, which is reflected in the degree of racemization (about 15%) for both reactions. It is found that cis isohumulone, obtained from trans isohumulone, is racemized for 45% in agreement with the reaction sequence humulone - trans isohumulone - humulone - cis isohumulone. Trans isohumulone obviously epimerizes to cis isohumulone via humulone in aqueous buffer solutions up to pH 12.0. Isomerization via the carbanion at C-5, which accounts for the epimerization of the humulinic acids (see 8.4.1.4.), may occur in stronger alkaline medium, but it is then competitive with degradation reactions. [Pg.116]


See other pages where Humulinic acids is mentioned: [Pg.168]    [Pg.46]    [Pg.99]    [Pg.100]    [Pg.101]    [Pg.103]    [Pg.106]    [Pg.107]    [Pg.113]    [Pg.441]    [Pg.228]    [Pg.129]    [Pg.251]    [Pg.651]    [Pg.283]    [Pg.285]    [Pg.53]    [Pg.59]    [Pg.74]    [Pg.88]    [Pg.91]   
See also in sourсe #XX -- [ Pg.485 , Pg.493 ]

See also in sourсe #XX -- [ Pg.895 , Pg.896 ]




SEARCH



Deacylated-anti-humulinic acid

Dehydrated humulinic acid

Humulin

© 2024 chempedia.info