TERPENOIDS 241 



Mirov cites several instances in which closely related species 

 have similar terpenes (for example, Pinus muricata, P. attenuata, 

 and P. radiata), and other cases in which closely related species have 

 quite different terpenes. 



One extremely interesting situation involving pure species was 

 reported by Mirov (1948). Pinus ponderosa contains ^-pinene and 

 limonene (however, the variety scopulorum consists mostly of 

 a-pinene instead of /5-pinene). P. jejfreyi, which some botanists con- 

 sider a variety of P. ponderosa, contains no terpenes but rather hep- 

 tanes. To complicate the matter further, P. jeffreyi in its chemical 

 attributes approaches more closely the group Macrocarpa than the 

 group Australia to which P. ponderosa belongs (heptane is found in 

 all three species comprising the Macrocarpa group). Also, similar 

 aldehydes are found in P. jeffreyi and the pines of the Macrocarpa 

 group. Furthermore, P. jeffreyi crosses in nature with both P. ponder- 

 osa and P. coulteri, the latter a member of Macrocarpa. According to 

 Mirov, P. jeffreyi possibly crosses more readily with P. coulteri. 



In the genus Mentha rather extensive chemical investigations 

 of the important flavoring substances have been conducted by nu- 

 merous investigators. Recently, genetic studies have advanced evidence 

 that a single pair of genes controls, directly or indirectly, the major 

 monoterpenic chemical constituents of mint oils (Murray, 1960a, 

 1960b). The action of the dominant gene apparently is upon a cyclic 

 intermediate to convert it to a spearmint (2-oxygenated-p-menthane), 

 while in the presence of the recessive only, the cyclic intermediate is 

 converted to the peppermint type (3-oxygenated-p-menthane) 

 (Reitsema, 1958a, 1958b). Except for the position of the oxygen a 

 corresponding series of compounds exists in both the peppermint and 

 spearmint lines. No authenticated instance of the coexistence of 

 spearmint and peppermint oils in a single plant exists. In general the 

 spearmint oils contain more unsaturated compounds and much more 

 saturated alcohols while odd side reaction products such as found in 

 some peppermint oils are lacking. A third group of species, the so-called 

 "lemon mints," do not produce cyclic derivatives but rather acychcs 

 such as citral and linalool. Reitsema has constructed a correlative 

 biochemical-phylogenetic sequence in which the progression is toward 

 increasingly more reduced compounds (Fig. 13-2). 



Some very interesting work on higher terpenes of the 

 Cucurbitaceae has been reported by Enslin and Rehm (1960). These 

 substances, not fully characterized, appear to be related to the 

 tetracyclic triterpenes. They are bitter tasting, have a purgative 

 action, and are referred to as "cucurbitacins." So far, eleven different 

 cucurbitacins are known, ten of which have been crystallized and an 

 empirical formula assigned to them. All contain two or more 



