Terpenoid aldehydes

Representatives of Xantholininae possess an unpaired nonreversible anal gland reservoir at their abdominal tip. As already reported, the secretion contains iridodial, actinidin, terpenoid aldehydes, ketones, limonene, and isopule-gol [8,118]. 

Table IV. Percentages of Methylation of Total Terpenoid Aldehydes in Pigment Glands of Various Gossypium Species and Hybrids with hirsutum...

Table V. Percentages of Raimondar in the Total Terpenoid Aldehydes from Pigment Glands of Gossypium Species and Their Hybrids with G.. raimondii...

The toxicity of the cotton terpenoid aldehydes to different larvae has been reported by several groups (227, 259, 270-275). These results are summarized in Table 2. Although there is variation in the test results among the different laboratories, it is obvious that gossypol and probably the other terpenoid aldehydes have a wide range of toxicity to many moth larvae. 

The classical Rosenmund reduction is quite broad in scope, and can be applied to fairly complex molecules. Not included in Table 3 are several examples giving terpenoid aldehydes which occur in yields of up to 88%.Nevertheless, there are serious limitations. The yields are variable, being affected by side reactions such as overreduction and decarbonylation (Scheme 4). Moreover, the high temperatures required and the production of free hydrogen chloride are obvious disadvantages. 

The flavour properties of the citrus oils are based on compounds like aldehydes, esters and alcohols. Aldehydes play the most important role in citrus flavours. Mainly the saturated C-8, C-10 and C-12 long-chain constituents as well as the terpenoid aldehydes citral (a mixture of neral and geranial) and citronellal form the basic notes of the fresh and pleasant citms flavour. Also sesquiterpene aldehydes and ketones, such as sinensal or nootkatone, are significant for citms flavours. The aldehyde content, therefore, is frequently used as a quality criterion for citms oils. Important citms alcohols are linalool, octanol, a-terpineol (especially in distilled lime oil) and ter-pinen-4-ol. Furthermore, esters contribute to the flavour properties of citms oils. Especially the acetates of geraniol and nerol and, to a lesser extent, citronellol are... 

Phillip, V. A. and Hedin, P. A. (1990). Spectral techniques for the structural analysis of the cotton terpenoid aldehydes gossypol and gossypolone. J. Agric. Food Chem. 38, 525-528. 

Stipanovic, R. D., Altman, D. W., Begin, D. L., Greenblatt, G. A., and Benedict, J. H. (1986). Effects of cotton terpenoid aldehydes on resistance to Heliothis. International Union of Pure and Applied Chemistry, Sixth Int. Congr. Pest. Chem. Ottawa, Canada, Abstract No. 2D/E-05. 

Fig. 1. Structure of naphthofuran and terpenoid aldehyde phytoalexins formed by gossypium species. See text for identifications.

Concentrations of constitutive terpenoids in the root epidermis of cotton are unrelated to differences in resistance. But concentrations of terpenoid aldehydes formed in the vicinity of the pericycle, near the head of the animal, act as phytoalexins and are closely correlated with levels of resistance (11, 48). Little or no phytoalexin is formed in the pericycle of susceptible cultivars. Mixtures of terpenoid phytoalexins are more toxic to the nematode than gossypol alone, and mixtures containing methylated terpenoid phytoalexins (from 6. hirsutum) are more toxic than those that contain only nonmethyTated phytoalexins (from 6. arboreum) (49). Thus, the structure of terpenoid phytoalexins also is importan for resistance to root knot nematode. 

Histochemical studies have shown that the phytoalexins are formed in paravascular parenchyma cells, and are exuded into xylem vessels (58). Since some parenchyma cells contain predominately dHG, it is possible that the naphthofurans alone are synthesized in the parenchyma cells and exuded into the vessels and intercel 1 ular spaces, where they readily oxidize to terpenoid aldehydes. 

Resistant, compared to susceptible, cultivars exhibit more rapid synthesis of terpenoid aldehyde phytoalexins in xylem vessels (16), and cadalene and lacinilene phytoalexins in cotyledonary tissue Q7), in response to X. campestris infection. Of the various compounds tested, 2,7-dihyciroxycadalene, followed by lacinilene C, had the greatest antibiotic activity against the bacterium. Lacinilene C exists as two optical isomers, which occur in different proportions in two different resistant cultivars. The (+)-lacinilene C is more than three times as toxic as (-)-lacinilene C (17). The toxicity of terpenoid aldehydes and their precursors have not been tested against the bacterium. 

We have examined these lethal reactions biochemically (93, unpublished). In all cases spontaneous defense reactions (phytoalexin synthesis, tannin synthesis and tannin oxidation) occur concurrent with the onset of symptoms. The quantities of terpenoid aldehydes and tannins found in tissues of severely affected plants are usually very similar to those found in severely diseased plants dying from microbial infections. Thus, it is possible that many of the disease symptoms seen in cotton are due to the toxic terpenoids and tannins formed in response to infections. 

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