Natural Products & Metabolomics

Apocynaceae is a botanical family distributed mainly in tropical and subtropical regions of the world. In Brazil, they comprise about 90 genera and 850 species, inhabiting various types of vegetation. Within this large botanical family, the genus Hancornia is considered monotypic, with its only species Hancornia speciosa Gomes. Antihypertensive, antidiabetic, and antiviral activities are described for this species. Despite having been the target of some studies, knowledge of its chemical composition is still limited. In this study, the phenolics of H. speciosa leaves were analyzed using ultra-high performance liquid chromatography (UHPLC) coupled to Orbitrap high-resolution mass spectrometry (HRMS). As a result, 14 compounds were identified viz. protocatechuic acid, catechin, and quercetin, and another 14 were putatively identified viz. B- and C-type procyanidins, while just one compound remained unknown. From the identified compounds, 17 are reported for the first time viz. coumaroylquinic acid isomers and eriodyctiol. The results show that Hancornia speciosa can serve as source of valuable phenolics.

Sarcophyton sp. soft corals are rich in cembranoid diterpenes, which represent the main chemical defense of corals against their natural predators in addition to their myriad biological effects in humans. Quantitative NMR (qNMR) was applied for assessing the diterpene variation in 16 soft coral specimens in the context of their genotype, origin, and growing habitat. qNMR revealed high diterpene levels in Sarcophyton sp. compared to Sinularia and Lobophyton, with (ent)sarcophines as major components (17–100 µg/mg) of the coral tissues. Multivariate data analysis was employed to classify samples based on the quantified level of diterpenes, and compared to the untargeted NMR approach. Results revealed that qNMR provided a stronger classification model of Sarcophyton sp. than untargeted NMR fingerprinting. Additionally, cytotoxicity of soft coral crude extracts was assessed against androgen-dependent prostate cancer cell lines (PC3) and androgen-independent colon cancer cell lines (HT-29), with IC50 values ranging from 10–60 µg/mL. No obvious correlation between the extracts’ IC50 values and their diterpene levels was found using either Spearman or Pearson correlations. This suggests that this type of bioactivity may not be easily predicted by NMR metabolomics in soft corals, or is not strongly correlated to measured diterpene levels.

Among most propagated and worldwide cacti used for commercial (food) production is Opuntia ficus-indica. The present study aimed at investigating aroma compound and metabolites distribution in cactus fruits from 3 cultivars (cvs): red ‘Rose’, yellow-orange ‘Gialla’ and greenish-white ‘Bianca’ represented by both its pulp and skin samples. Two methods were applied including UV-vis fingerprinting versus gas chromatography coupled to mass spectrometry (GC-MS). Betalains predominated in red fruits, whereas carotenoids and chlorophyll were more abundant in orange and green fruits, respectively, as revealed from their crude extracts UV absorption spectra. Volatiles were profiled using headspace solid-phase micro-extraction (SPME) coupled to GC-MS. 40 Volatiles were identified with short chain aldehydes (25–32%) and acids (25–29%) as the major volatile classes. Cultivars exhibited comparable aroma profiles suggesting that volatiles cannot serve as a chemical fingerprint to distinguish between cvs. Primary metabolites mediating for fruit taste and nutritional value viz. sugars and amino acid were profiled using GC-MS post silylation with 82 identified metabolites. Glucose (62%) and fructose (16%) were found to predominate sugar composition, whereas proline was the major amino acid (3–8%). Multivariate data analyses revealed for betalain and disaccharides enrichment i.e., turanose and sucrose in fruit skin versus proline, talopyranose and lyxopyranose abundance in pulp tissue.

The chemical composition of the hydrodistilled leaf essential oil from Chenopodium ambrosioides L. growing wild in Yemen was determined by GC-MS analysis, and its cytotoxic, and general antioxidant potential were evaluated. Major compounds of C. ambrosioides oil were ascaridole (54.2%), isoascaridole (27.7%) and p-cymene (8.1%). At concentrations of 50 and 25 μg/mL, the essential oil showed cytotoxic activity against HT29 (human colon adenocarcinoma cells), with growth inhibition of 100 and 56% (± 3). The free radical scavenging ability of the oil was assessed by the DPPH assay to show antiradical activity with IC50 of 10.4 μg/mL. TLC-bioautographic assay was used to identify the acetylcholinesterase inhibitory effect, and ascaridole was isolated and characterized (ESIMS, 1H NMR, 13C NMR and HMBC) as the responsible constituent for anticholinesterase activity.

Hydnora abyssinica A.Br. (Hydnoraceae), a holoparasitic herb, is for the first time recorded for Abyan governorate of South Yemen. Flowers of this species were studied for their ethnobotanical, biological and chemical properties for the first time. In South Yemen, they are traditionally used as wild food and to cure stomach diseases, gastric ulcer and cancer. Phytochemical analysis of the extracts showed the presence of terpenes, tannins, phenols, and flavonoids. The volatile components of the air-dried powdered flowers were identified using a static headspace GC/MS analysis as acetic acid, ethyl acetate, sabinene, α-terpinene, (+)-D-limonene and γ-terpinene. These volatile compounds that characterize the odor and taste of the flowers were detected for the first time in a species of the family Hydnoraceae. The flowers were extracted by n-hexane, dichlormethane, ethyl acetate, ethanol, methanol and water. With exception of the water extract all extracts demonstrated activities against Gram-positive bacteria as well as remarkable radical scavenging activities in DPPH assay. Ethyl acetate, methanol and water extracts exhibited good antifungal activities. The cytotoxic activity of the extracts against FL cells, measured in neutral red assay, was only weak (IC50 > 500 μg /mL). The results justify the traditional use of the flowers of Hydnora abyssinica in South Yemen.

A new dihydroflavonol–flavonol biflavonoid derivative, named ericoside was isolated from the ethanol extract of the whole plant of Erica mannii along with the known flavonoid, taxifolin 3-O-α-l-rhamnopyranoside; and two readily available sterols (sitosterol, sitosterol 3-O-β-d-glucopyranoside). The isolation was performed using chromatographic methods and the structure of purified molecules were elucidated using spectroscopic techniques (e.g. MS, NMR) and by comparison with literature data. The crude ethanol extract, ericoside, and taxifolin 3-O-α-l-rhamnopyranoside were tested against ten Gram-negative bacteria including multidrug resistant clinical isolates using a broth microdilution method. The crude ethanol extract showed no noteworthy activity. Of the purified compounds, ericoside displayed moderate activity against the resistant Escherichia coli AG100 with a MIC of 64 μg/mL.

Marine life has developed unique metabolic and physiologic capabilities and advanced symbiotic relationships to survive in the varied and complex marine ecosystems. Herein, metabolite composition of the soft coral genus Sarcophyton was profiled with respect to its species and different habitats along the coastal Egyptian Red Sea via 1H NMR and ultra performance liquid chromatography-mass spectrometry (UPLC–MS) large-scale metabolomics analyses. The current study extends the application of comparative secondary metabolite profiling from plants to corals revealing for metabolite compositional differences among its species via a comparative MS and NMR approach. This was applied for the first time to investigate the metabolism of 16 Sarcophyton species in the context of their genetic diversity or growth habitat. Under optimized conditions, we were able to simultaneously identify 120 metabolites including 65 diterpenes, 8 sesquiterpenes, 18 sterols, and 15 oxylipids. Principal component analysis (PCA) and orthogonal projection to latent structures-discriminant analysis (OPLS) were used to define both similarities and differences among samples. For a compound based classification of coral species, UPLC–MS was found to be more effective than NMR. The main differentiations emanate from cembranoids and oxylipids. The specific metabolites that contribute to discrimination between soft corals of S. ehrenbergi from the three different growing habitats also belonged to cembrane type diterpenes, with aquarium S. ehrenbergi corals being less enriched in cembranoids compared to sea corals. PCA using either NMR or UPLC–MS data sets was found equally effective in predicting the species origin of unknown Sarcophyton. Cyclopropane containing sterols observed in abundance in corals may act as cellular membrane protectant against the action of coral toxins, that is, cembranoids.

Date palm fruit (Phoenix dactylifera) is not only one of the most economically significant plants in the Middle East, but also valued for its nutritional impact, and for which development of analytical methods is ongoing to help distinguish its many cultivars. This study attempts to characterize the primary and secondary metabolite profiles of 18 date cultivars from Saudi Arabia. A total of 44 metabolites extracted from the fruit peel were evaluated in a UPLC-qTOF-MS based metabolomics analysis including flavonoids, phenolic acids and fatty acids. The predominant flavones were glycosides of luteolin and chrysoeriol, as well as quercetin conjugates, whereas caffeoyl shikimic acid was the main hydroxycinnamic acid conjugate. GC-MS was further utilized to identify the primary metabolites in fruits (i.e. sugars) with glucose and fructose accounting for up to 95% of TIC among most cultivars. PCA and OPLS analyses revealed that flavone versus flavonol distribution in fruit were the main contributors for cultivar segregation. The antioxidant activity of date fruit samples was correlated with their total phenolics as determined by DPPH and CUPRAC assays. Dkheni Saudi and Shalabi Madina cultivars, appearing as the most distant in clustering analyses exhibited the strongest antioxidant effect suggesting that multivariate data analysis could help determine which date cultivars ought to be prioritized for future agricultural development.

Passiflora incarnata as well as some other Passiflora species are reported to possess anxiolytic and sedative activity and to treat various CNS disorders. The medicinal use of only a few Passiflora species has been scientifically verified. There are over 400 species in the Passiflora genus worldwide, most of which have been little characterized in terms of phytochemical or pharmacological properties. Herein, large-scale multi-targeted metabolic profiling and fingerprinting techniques were utilized to help gain a broader insight into Passiflora species leaves’ chemical composition. Nuclear magnetic resonance spectroscopy (NMR) and mass spectrometry (MS) spectra of extracted components derived from 17 Passiflora accessions and from different geographical origins were analyzed using multivariate data analyses. A total of 78 metabolites were tentatively identified, that is, 20 C-flavonoids, 8 O-flavonoids, 21 C, O-flavonoids, 2 cyanogenic glycosides, and 23 fatty acid conjugates, of which several flavonoid conjugates are for the first time to be reported in Passiflora spp. To the best of our knowledge, this study provides the most complete map for secondary metabolite distribution within that genus. Major signals in 1H-NMR and MS spectra contributing to species discrimination were assigned to those of C-flavonoids including isovitexin-2″-O-xyloside, luteolin-C-deoxyhexoside-O-hexoside, schaftoside, isovitexin, and isoorientin. P. incarnata was found most enriched in C-flavonoids, justifying its use as an official drug within that genus. Compared to NMR, LC-MS was found more effective in sample classification based on genetic and/ or geographical origin as revealed from derived multivariate data analyses. Novel insight on metabolite candidates to mediate for Passiflora CNS sedative effects is also presented.

In recent years, many new enzymes, like glutaminyl cyclase (QC), could be associated with pathophysiological processes and represent targets for many diseases, so that enzyme-inhibiting properties of natural substances are becoming increasingly important. In different studies, the pathophysiology connection of QC to various diseases including Alzheimer’s disease (AD) was described. Algae are known for the ability to synthesize complex and highly-diverse compounds with specific enzyme inhibition properties. Therefore, we screened different algae species for the presence of QC inhibiting metabolites using a new “Reverse Metabolomics” technique including an Activity-correlation Analysis (AcorA), which is based on the correlation of bioactivities to mass spectral data with the aid of mathematic informatics deconvolution. Thus, three QC inhibiting compounds from microalgae belonging to the family of sulfolipids were identified. The compounds showed a QC inhibition of 81% and 76% at concentrations of 0.25 mg/mL and 0.025 mg/mL, respectively. Thus, for the first time, sulfolipids are identified as QC inhibiting compounds and possess substructures with the required pharmacophore qualities. They represent a new lead structure for QC inhibitors.