Piquerol

Studies on Piqueria trinervia. A very interesting study is that of the allelopathic potential of Piqueria trinervia and its piquerols A and B, by Gonzalez de la Parra et al. (14). It was found that this widely distributed weed in the Valley of Mexico has a wide biological activity upon other plants. 

Cruz-Ortega, R., Anaya, A. L., Gavilanes-Ruiz, M., Sanchez-Nieto, S., and Jimenez-Estrada, M. 1990. Effect of diacetyl piquerol on the H+-ATPase activity of microsomes from Ipomoea purpurea. J. Chem. Ecol. 16, 2253-2261... 

Preliminary evidence suggest that piquerol A (26a) can be a potential resource in the control of Chagas disease (American trypanosomiasis), an endemic illness which afflicts millions of people in Latin America [116]. The causal agent is the protozoan Trypanosoma cruzi, which is transmitted by insect vectors. 

Piquerol A (26a), at concentrations equal or higher than 200 Xg/ml, arrested during four days the reproduction of T. cruzi epimastigotes in... 

Preliminary results from our laboratory have also shown that piquerol A can induce a 100% of mortality of the yellow fever (Aedes aegypti) and common mosquito Culex quinquefasciatus) larvae. Effective concentration ranged from 400-500 PPM [120]. 

The acaricidal activity of Piquerols A and B against the common cattle ticks Boophilus microplus was also tested [59]. Both compounds induced 100% mortality at a concentration of 300 Xg/ml on larvae and gravid female ticks. TTieir activity was similar to that exhibited by commercial organophosphorus acaricides tested with the same protocol and at similar concentrations. However, piquerol A and B did not prevented ovoposition as the organophosphorus acaricides did [122]. 

Piqueria trinervia possible herbicidal activity has been thoroughly studied. It was first demonstrated that piquerol A (26a) inhibited the germination and plant growth of several weeds, therefore it was proposed as responsible of P. trinervia allelopathic activity [52]. The mechanism of action of piquerol A was next studied [53]. This compound inhibited ATP synthesis and phosphorylating electron rate in pea chloroplasts. On the... 

Other hand, H+-uptake, basal and uncoupled electron transport were not affected. The acetylation of 26a yielded piquerol diacetate (26b) increasing its lipophilicity and photophosphorylation capacity [53]. 

It is well known that synthetic phenol and hydroquinones have herbicidal activity [54-56]. This finding led us to transform piquerol A to related compounds and examine their effects on the weeds Amaranthus hypocondriacus and Echinocloa crusgalli [123]. Piquerol A diacetate (26b), as well as, the benzylic alcohol (27), dialkilhydroquinone (28), and phenolic (29, 30,31) derivatives were prepared as indicated below "Fig. (7)."... 

Fig. (7). Transformation of piquerol A (26a) to diacetate (26b), benzylic alcoliol (27), dialkylliydroquinone (28) and phenolic derivatives (29, 30, 31).

Several piquerol derivatives inhibited, at a concentration of 100 PPM, radicle growth of two weeds (Table 3). Best results were obtained with the... 

Table 3. Effect of Piquerol A (26a) and its Derivative (26b-29) on the Radical Growth %) of Amarantus hypocondriacus and Echinocloa crusgalli...

Fig. (8). Proposed aromatic intermediate in the allelopathic activity of piquerol A.

Other monoterpenes such as espintanol [172] and piquerol A [173] have been early described as antiparasites. More recently, it has been reported that amino and methoxy goups significantly enhance citotoxic and antileishmanial potentials in thymol synthetic derivatives, suggesting these natural compounds should be considered lead structures for novel antileishmanial drugs to be used in oral therapy [174] (Fig. 19). 

Pioneering plants of disturbed habitats often produce active monoterpenes. (+ )-Pulegone (29) was four times, and (-1-)- and ( —)-camphor two times more toxic to seeds and seedlings of Raphanus sativus (Brassicaceae) than HCN (Asplund, 1968). The Mexican plant Piqueria trinervia (As-teraceae) produced monoterpene diols, piquerol A (82) and B (83), that strongly inhibited root and stem growth of competing plants at 50-200 ppm. 

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