PREPARATION OF TRANS-ISO-ALPHA ACIDS AND USE OF THEIR DICYCLOHEXYLAMINE SALTS AS A STANDARD FOR ISO-ALPHA ACIDS ANALYSIS

Abstract

The reaction between dicyclohexylamine and iso-alpha acids yields a crystalline product which consists of the dicyclohexylamine salts of trans-iso-cohumulone, trans-isohumulone and trans-iso-adhumulone. The presence of only the trans-isomers in the crystalline product was established by proton and carbon NMR. Pure trans-iso-alpha acids can be regenerated from the salt either by treatment with acid or in situ by the use of acidic buffers during HPLC analysis. The dicyclohexylamine salts of the trans-iso-alpha acids are stable for extended periods at room temperature, unlike the purified trans-iso-alpha acids, and are thus suitable for use as a standard for iso-alpha acids analysis.