Solution to angels’ share challenge

Abstract

The substance sought in the angels’ share challenge [1] is whisky lactone (Formula 1). To the best of our knowledge, whisky lactone was first reported by Webb et al. [2] in 1969. The peak which appears in the gas-chromatographic trailing edge of the large 2-phenylethyl alcohol peak was initially dubbed “peak 48 lactone.” From “a relatively poor infrared spectrum” it was suggested that the compound was a branched-chain isomer of the C9 lactone. In 1971 the two diastereomers of this substance were described by Masuda and Nishimura [3] as “quercus lactones-a and -b,” which they isolated from the wood of three oaks. Suomalainen and Nykanen [4] reported an isomer of the 4-hydroxy-3-methyloctanoic acid γ-lactone in eight different samples of whisky. They named it “whiskey lactone.” In 1972, Kepner et al. [5] identified the trans diastereomer as a constituent of the oak-wood agent in Cabernet Sauvignon wines by the gas-chromatographic retention times and the infrared, mass, and nuclear magnetic resonance (NMR) spectra. They suggested “that the compound is extracted from oak barrels during aging of the wine.” Numerous studies of this lactone appeared in the following years, and most of the reports proposed a new name for the compound. Other than this “notation jumble,” the correct assignment of the four possible stereoisomers also encountered difficulties in the past. It was only in 1986 that Gunther andMosandl [6] synthesized and separated the four stereoisomers of the lactone on a preparative scale and provided sensory characteristics for all the isomers. A historical review of this subject was provided by Maga [7] in 1996 (Fig. 1).