Robert P. Adams*, Philip S. Beauchamp, Vasu Dev and Stephen M. Dutz

Abstract: Re-examination of the leaf essential oils of the one-seeded, serrate leaf junipers of the Southwestern United States and northern Mexico, by GC, GC/MS and NMR, has yielded 2-ethenyl-3-methyl phenol (coahuilensol), 2-ethenyl-3-methyl anisole (coahuilensol, methyl ether), and 2-(1’-acetoxyethyl)-3-methyl anisole (pinchotene acetate) as new natural products. A survey of Juniperus oils revealed that these compounds were found in: three serrate leaf junipers (J. angosturana, two varieties of J. coahuilensis, and J. pinchotii). Coahuilensol was also found in the oils of two smooth leaf junipers of the western hemisphere (J. virginiana var. virginiana and J. v. var. silicicola); three multiple seeded, smooth leaf junipers of the eastern hemisphere (J. semiglobosa, J. semiglobosa var. talassica, and J. thurifera). The phenolic compounds were not found in section Juniperus, section Caryocedrus or in the one seeded, smooth leaf junipers of the eastern hemisphere. Coahuilensol has been previously reported as 2-(2-propenyl)-phenol (tentative). The leaf oils of J. angosturana J. coahuilensis, J. coahuilensis var. coahuilensis, J. monosperma and J. pinchotii were re-examined based on fresh oil collections and the compositions are reported. NMR data and mass spectra of the three 3-methyl phenols are presented to aid in future identification.

The compositions of the leaf essential oils of the one-seeded, serrate leaf junipers of the Southwestern United States and northern Mexico were first reported by Adams et al. in 1981 (1). Several phenolic components were unidentified. The major unidentified phenolic compound was tentatively identified as 2-(2-propenyl)-phenol. In one of the subsequent reports on the composition of the leaf oils of serrate leaf junipers (2,3), these phenolic compounds were still unidentified. A reexamination of the leaf oil of J. coahuilensis var. arizonica from Rock Round State Park, NM, showed a considerable amount of these phenolic compounds in these plants. It was possible to do preparative work to isolate these compounds for NMR structural determination. The group of serrate leaf margined Juniperus species of the western hemisphere appears to be a natural division of Juniperus, section Sabina (4). These junipers are characterized by having microscopic (40 X) serrations (teeth) on the scale leaves and these taxa are generally xerophytes, occurring in the great North American deserts and arid mountains adjacent to the deserts (4). The serrate leaf junipers range from northern Guatemala, into Mexico, thence northward into the southwestern United States, as far north as Oregon (J. occidentalis) and eastward to Arkansas (J. ashei). The group is thought to had been a part of the Madro-Tertiary flora dating from pre-Eocene (5). As the neotropical tertiary geoflora expanded into the drying conditions that created the southwestern deserts, Axlerod (5) hypothesized that there was a rapid evolution of new species. In this paper, we report a re-examination of the leaf essential oils of J. angosturana J. coahuilensis var. coahuilensis, J. coahuilensis var. coahuilensis, J. monosperma and J. pinchotii, junipers of the southwestern US and northern Mexico. Some discussion is needed to facilitate recent nomenclature changes (4). Juniperus erythrocarpa, the taxon in trans-Pecos, Texas and Mexico is now treated as J. coahuilensis var. coahuilensis in trans-Pecos, Texas and Mexico and as J. coahuilensis var. arizonica in Arizona and New Mexico ; J. monosperma var. gracilis Mart., from north-central Mexico, is now J. angosturana R. P. Adams (4). Juniperus monsperma, previously reported from Mexico, is now thought to be confined to the United States (4).