Assessment, Validation and Application to Real Samples of an RP-HPLC Method for the Determination of Guayulins A, B, C and D in Guayule Shrub

Abstract

Guayule (Parthenium argentatum Gray) is a shrub native to the arid regions of Mexico. In the last decades, significant attention to its cultivation has arisen because it is the raw material for the production of hypoallergenic natural rubber. Guayule biomass also contains high amounts of resin, which is not normally exploited in any way. Among other sesquiterpenic esters, guayulins (i.e., the parteniol esters of cinnamic acid, guayulin A, or of anisic acid, guayulin B) are contained in resin. In addition, minor amounts of guayulin C and guayulin D are formed by degradation/oxidation of guayulins A and B, respectively. Guayulins likely act as cinnamate and p-anisate reservoirs for the Guayule shrub; in addition, it has been postulated that they might have a key role in the chemical defense system of Guayule. Furthermore, it seems reasonable that guayulins may possess significant biological properties (e.g., antibacterial and anticancer activities), in close analogy with those shown by sesquiterpene lactones contained in many other species of Parthenum genus. As a matter of fact, guayulins A and B play an important role in the synthesis of antineoplastics used in breast cancer treatment. In this contribution we propose an original and validated RP-HPLC approach to the simultaneous quantification of guayulins A, B, C and D. The procedure of resin extraction from Guayule biomass has been optimized in terms of both extraction method and solvent. RP-HPLC separation has been accomplished by an Ascentis ® C18 column under isocratic elution with a 80:20 (v:v) acetonitrile:water mixture. Validation was carried out in terms of limits of detection and quantification, linearity, precision, and trueness. Finally, the method was tested with a number of fresh and seasoned samples of spontaneous Guayule shrub from Mexico.

Effect of Seasonal Decrease in Temperature on the Content and Composition of Guayulins in Stems of Guayule (Parthenium argentatum, Gray)

“…During this study, the difficulty emerged when no commercial standards of guayulins were available. Those that had been used by other authors before were no longer available [1]. It was only possible to isolate guayulin A in our laboratory with enough purity to be considered as standard.…”

“…The guayulin family of sesquiterpene secondary metabolites comprises four known members, guayulin A-D [1,2], although several other members may exist [3,4]. Guayulin A was first isolated in 1911 and its structure was determined some years later [5,6].…”

Guayule (Parthenium argentatum A. Gray), a Renewable Resource for Natural Polyisoprene and Resin: Composition, Processes and Applications

“…Guayulins A and B have been shown to possess biological properties and to have a key role in the defense of the plant. They actually act as biological triggers in the synthesis of lychnostatine and paclitaxel, which are agents used in breast cancer treatment [ 113 , 114 ].…”

Potential Applications of Guayulins to Improve Feasibility of Guayule Cultivation

“…This is because guayulins C and D are often absent from freshly prepared acetone extracts [19] of guayule tissues. However, fresh extracts of leaves contained as much C and D as A and B, suggested that they were actively synthesized in the leaves, and not generated by oxidation post-extraction [21]. [19,22]).…”

“…Although large quantities of guayulins can be found [19,21] and have potential applications as sesquiterpenes, there are few guayulin-specific reports in the scientific literature. Only 17 records were found in searchable databases (Web of Science, Scopus and PubMed) when the term "guayulin" is searched as relevant in title or abstract or keyword.…”