The substance known as "isohumulone" is in fact a mixture of four components. They were separated by C.C.D. According to a new nomenclature based mainly on the chemically related humulinic acids A,B, C etc. series they are the stereoisomers isohumulone A and B (IV and V) and alloisohumulone A and B (VI and VII).From the reaction with iodine it was deduced earlier (1) that the isomerization mixture of humulone (I) contained not only isomer 11, but also isomer 111. Counter current distribution (C.C.D.) with a large number of transfers has now revealed that both isomer I1 and I11 are still a mixture of two components each. The proton magnetic resonance (PMR) spectra of these compounds prove that they are the stereoisomers IV, V, VI and VII and are therefore structurally related to the humulinic acids A and B (29394).It is suggested to use the suffix A for substances in this field having the alkenyl chain and the hydroxyl group in trans position. The compound with a cis configuration of these substituents receives then the B suffix to its name. Substances IV and V are then isohumulone A and isohumulone B respectively.Earlier meanings for the A, B etc. suffixes should be dropped. Substances VI and VII will be called alloisohumulones and are respectively again the A and B compound.Alloisohumulones are formed by isomerization of humulone in boiling phosphate buffer adjusted to pH 9.0 at 250, and also by the iso-(*) This is the 44th paper on hop constituents from our laboratory. (1964).

Isomerization of tetrahydrohumulone can be accompanied by oxidation, since cis tetrahydrohumulinone is isolated from the reaction mixture. This compound can also be obtained by heat‐induced isomerization of the known tetrahydrohumulinone, which is the trans form. By similar isomerization of the known humulinone, cis humulinone was prepared: this is probably an important intermediate produced from humulone during wort boiling. Trans and cis oxyhumulinic acids have been isolated for the first time. The conductivity of the boronate ester complexes of the humulinones and the oxyhumulinic acids confirms their trans or cis structures, as deduced from PMR characteristics.

Humulink acid contains chiral centra at C4 and C6 and can therefore theoreti cally occur in four optically active stereoisomers. The diastereoisomeric forms are at the same time trans and e/s isomers of each other (formerly humulinic acids A and B).» This paper concerns the isolation and characterization of the tram and els co-and ad-humulinic acids and the separation of racemic trans humulinic acid in its enantiomorphs.

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Diastereoisomeric mixtures of 2-methylcyclopentano1 (I), 2-methylcyclohexanol (11) and 2-methylcycloheptano1 (111) can be separated in very good yields into the Cis and trans isomers by counter current distribution. A suitable method for isolation is also given.