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The argentatins are the most abundant compounds in guayule resin with promising potential for the biopharmaceutical industry. However, their accumulation along the vegetative cycle of the plant and their quantification in different guayule accessions has not been assessed. The present study established the profile of 16 known compounds of the argentatin family in 27 guayule and guayule interspecific accessions using UHPLC-Q-Orbitrap-HRMS. In addition, the structure of five unreported argentatins was tentatively identified. All compounds were present in all accessions (27) and samples (135) analyzed, although in varying amounts. Those compounds found in the highest proportion were argentatins A, B, C, G, isoargentatin A, 16-dehydroargentatin C and quisquagenin. The mass spectra of the compounds were more complex than expected, revealing the lability of the compounds and a high probability to partially degrade during analysis, even at the mildest ionization energies. Based on available standards, argentatins A and B and isoargentatins A and B were quantified in 27 accessions and five samplings along the growing season. The total abundance of the four compounds was 13.4–39.6% of the guayule resin in stems depending on the accession. The profiles of accumulation were related to the genetic origin, with the summer and spring periods producing the greatest yield of argentatins. Pure guayule accessions generally produced more argentatins than hybrids, although the most productive for argentatins and isoargentatins A and B was the non-mariola hybrid AZ-3. • Twenty-one argentatins and related compounds were found in 27 guayule accessions. • Major compounds were argentatins A, B, C, G, isoargentatin A and 16-dehydroargentatin C. • The argentatins profile of accumulation was related to the genetic origin. • Pure guayule accessions produced more argentatins than hybrids. • Four compounds' account for 13.4–39.6% of the resin depending on the accession. [ABSTRACT FROM AUTHOR]

The guayulin content of guayule (Parthenium argentatum Gray) is subject to seasonal variation and follows specific patterns that are dependent on the accession and the organ (stems or leaves). However, little is known about guayulin in response to agronomic management such as irrigation or fertilization. A 24-month experiment was performed to investigate the accumulation of guayulin in one guayule accession (R-1040) and two hybrids (CAL-1 and AZ-2), in relation to crop system (irrigated or non-irrigated) and the nitrogen fertilizer units (NFU 0% or 100%). Irrigation increased biomass, which likely diluted guayulin concentration, but contributed to increase guayulins yield in both organs (stems and leaves). Fertilization had no effect on guayulin and resin production, but it increased the number of stems and total biomass. The pattern of accumulation of guayulins between stems and leaves was different. Differences were observed between the hybrids and the pure accession R1040, which was smaller in size but produced more guayulins. A strong relationship was found between guayulin yield and the production of rubber. • Hybrids accessions AZ-2 and CAL-1 behaved differently from pure guayule R1040. • Accession and harvest factors had the most significant effects on guayulin content. • Irrigation and fertilization interaction diluted drastically the concentration of guayulins. • Guayulins C and D seem to play a relevant role in the guayulins accumulation. • Strong correlation exists between guayulins and rubber content. [ABSTRACT FROM AUTHOR]

Guayule (Parthenium argentatum A. Gray) exploitation has so far been focused on the production of rubber, but until now was unable to compete commercially, as other guayule co-products have not been equally considered for exploitation. However, to successfully exploit one of these co-products, the guayulins, it will be necessary to establish a robust resin extraction method that maximizes the yield of guayulin compounds for downstream purification. For this purpose, different resin extraction conditions (solvent, temperature, number and time of cycles, and plant material:solvent ratio) were evaluated to select those that produced a resin with a higher guayulins yield. First, accelerated solvent extraction (ASE) was performed using three solvents (ethanol, acetonitrile, and acetone) at three different temperatures (40, 56, and 80 °C) and two cycle times (5 and 20 min) to narrow down the conditions. Then, an industrial scale process was simulated with warm solvent extraction (WSE) using acetone and acetonitrile only at five different cycle times (30, 45, 60, 120, and 180 min). Finally, WSE performance was optimized using four different plant material:solvent ratios (1:20, 1:10, 1:5, and 1:3), and three consecutive extraction cycles. Results from the ASE studies revealed, as expected, that solvent choice had the greatest influence on resin and guayulins yield and allowed to discard ethanol as a suitable extraction solvent while acetonitrile performed best for guayulin extraction. No tangible differences in resin yield were observed in WSE studies between the different process parameters, but they were differences in guayulin extraction. Short cycle times worked best with both solvents, and again, acetonitrile was more selectively extracted guayulins, especially for the polar guayulins C and D. Finally, WSE optimization showed that a 1:5 plant material:solvent ratio and two extraction cycles were the best compromise in terms of guayulins yield and time/cost effectiveness. • Solvent followed by temperature had the greatest influence on resin and guayulins yield. • Acetonitrile and acetone performed better with two cycles and shorter times. • Acetonitrile at 30 min extracts the highest guayulins content, specially guayulins C and D. • Guayulin concentration assessment should be done in mg per extraction and in mg per g of resin. [ABSTRACT FROM AUTHOR]

Guayule (Parthenium argentatum , A. Gray) is a promising alternative source to natural rubber from Hevea brasiliensis L. Recently, another important fraction of its composition, the resin, has been the focus of many studies due to its promising commercial applicability. In the resin extract there are guayulins (A, B, C and D), belonging to the sesquiterpene family, which are usually analyzed by HPLC-DAD and, lately, with other labor-intensive analytical techniques. Near infrared spectroscopy (NIR) has been successfully used in fresh guayule and dry biomass to assess moisture, and total rubber and resin content. The purpose of the present study is to estimate, for the first time ever, the detailed guayulin content in guayule dry stems using NIR spectroscopy. So, a set of 144 samples were analyzed by a Perkin Elmer Spectrum One FT-NIR equipment coupled with a near infrared reflectance accessory (NIRA). In addition, guayulins A and B standards, isolated in the lab, were scanned to generate the best partial least squares regression (PLSR) model. The best correlative PLSR models for resin, rubber and guayulins were developed within the range of 1100–2500 nm, showing an excellent calibration correlation (r 2 c = 0.92–1.00) and cross validation (r 2 cv = 0.87–0.92). The residual predicative deviation (RPD) was above 3 in the case of resin, rubber and guayulins A, B and D; while in guayulin C was 2.8. These high RPD values demonstrated a good prediction power of the model. In conclusion, the use of NIR spectroscopy for the estimation of resin and guayulin content in ground guayule stems is an excellent option for the routine analysis instead of time-consuming and labor-intensive traditional techniques. • Guayulin A, B, C, and D quantification by near infrared spectroscopy in guayule dry stems is achieved for first time. • Near infrared spectroscopy is an excellent technique for the analysis of rubber, resin and guayulins in guayule. • The best correlative partial least squares regression models were developed within the range of 1100–2500 nm. [ABSTRACT FROM AUTHOR]

In the rubber extraction process, guayule leaves represent an important biomass waste by-product, up to 32%, whose exploitation might contribute to the valorization of the whole plant. The extraction of any of its bioactive compounds or its use as an antioxidant seems to be the most feasible alternative. This study relates guayule leaves morphology to the individual content of 35 compounds (of the 50 tentatively identified), the determination of overall phenolic content and antioxidant activity. The morphological traits allowed the classification of the accessions (27) into three main groups according to size and shape of the leaf, being related to their hybridization. The environment and growing conditions modified the leaf phenotype for USDA germplasm with respect to recent USA studies. The heterogeneity found by different authors in the determination of phenolic content in guayule leaves requires a standardization procedure. Of the two analysis protocols, Total Polyphenol Index (TPI) and Folin–Ciocalteau reagent (Folin) after extracting the leaves at 1 and 24 h, the TPI at 1 h was selected since it was faster and simpler than others and correlated better with the antioxidant activity determined by 2,2-diphenyl-picrylhydrazyl (DPPH). The compounds found in greater quantities corresponded to the chlorogenic acid family, but with no influence with leaf morphology. On the other hand, compounds with smaller concentrations such as gallic acid, an isomer of ferulic acid or the quercetagetin methyl ether glucuronide correlate with aspects of leaf morphology. • Leaves morphological traits allowed the classification of 27 guayule accessions. • Antioxidant activity varied among the accession and the content of phenolic compounds. • Total polyphenolic index of leaves is proposed as standard method. • Fifty phenolic compounds were tentatively identified by LC-MS in guayule leaves. [ABSTRACT FROM AUTHOR]

• Chromatographic guayulin analysis benefits from smaller, narrower columns. • Mass spectrometric analysis of guayulins should be extended. • There are more than four compounds within the guayulin family. • Guayulin content decreases when rubber biosynthesis is induced. • There may be a connection between guayulins and rubber metabolic processes. Guayule (Parthenium argentatum Gray) is a promising alternative and renewable source of natural rubber/latex. There is a general acceptance that to successfully industrialize the cultivation of guayule, it will be necessary to valorize all of its co-products, including resins, which can reach 16 % of weight of dry matter. Guayule resins have been reported to have antifungal, insect antifeedant and wood protector activities, although it remains to be clearly established which compounds are responsible for such actions. Here, we focus on a terpene family present in guayule resin that is a candidate for these activities, the sesquiterpenes, which are present in significant amounts (10–15 %). We studies the versatility of the most common analytical method used in their analysis, HPLC-UV, with mass spectrometry techniques including LC–MS, ESI-TOF and MALDI-TOF to address the following objectives: 1) to explore whether there are other members of the guayulins family, 2) to determine the applicability of new methods based on mass spectrometry, and 3) to establish the relationship between the four known major guayulins in the seasonal changes described by other authors. Our results have allowed us to: tentatively identify a new member of this family and to suggest the existence of others; propose changes to the chromatographic approaches currently used; extend the use of mass spectrometry (direct identification and monitoring of purification of guayulins); and finally, demonstrate that the content of guayulins A and B decreases at the start of winter when the most active period of natural rubber biosynthesis begins. [ABSTRACT FROM AUTHOR]