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Steviol glycosides (SvGls) are plant secondary metabolites belonging to a class of chemical compounds known as diterpenes. SvGls have been discovered only in a few plant species, including in the leaves of Stevia rebaudiana Bertoni. Over the last few decades, SvGls have been extensively researched for their extraordinary sweetness. As a result, the nutritional and pharmacological benefits of these secondary metabolites have grown increasingly apparent. In the near future, SvGls may become a basic, low-calorie, and potent sweetener in the growing natural foods market, and a natural anti-diabetic remedy, a highly competitive alternative to commercially available synthetic drugs. Commercial cultivation of stevia plants and the technologies of SvGls extraction and purification from plant material have already been introduced in many countries. However, new conventional and biotechnological solutions are still being sought to increase the level of SvGls in plants. Since many aspects related to the biochemistry and metabolism of SvGls in vivo, as well as their relationship to the overall physiology of S. rebaudiana are not yet understood, there is also a great need for in-depth scientific research on this topic. Such research may have positive impact on optimization of the profile and SvGls concentration in plants and thus lead to obtaining desired yield. This research summarizes the latest approaches and developments in SvGls production. Key points: • Steviol glycosides (SvGls) are found in nature in S. rebaudiana plants. • They exhibit nutraceutical properties. • This review provides an insight on different approaches to produce SvGls. • The areas of research that still need to be explored have been identified. [ABSTRACT FROM AUTHOR]

Stevia rebaudiana Bertoni is a shrub commonly called 'stevia' belonging to the Asteraceae family, cultivated in many regions worldwide. Its main characteristic is the presence of sweetening metabolites, steviol glycosides (StGlys), having up to 300 times more sweetening capacity than a 0.4% solution of sucrose. StGlys have made this species extremely relevant for the food and beverage industries, gaining greater industrial and scientific interest in recent years. However, more plant material production is needed to meet the increased demand of the global market. In addition, stevia has a wide variety of properties that offer benefits against many health problems, such as polyphenols and terpenoids, as well as phytosterols and vitamins, highlighting the importance of its consumption and commercialization. Thus, considering the current great notoriety of the species, the purpose was to compile studies from the characterization of seeds to their industrial and safety applications, addressing biotechnological strategies to understand, stimulate, and improve the biosynthesis of stevia plant metabolites. In addition to providing useful information for plant breeding and/or high-quality seeds, large-scale cultivation, and leaf biomass production. • A comprehensive review of the safety of natural sweeteners obtained from S. rebaudiana is provided. • Photoperiod variation influences the biomass productivity of S. rebaudiana. • Different production systems for producing fertile seeds and obtaining quality biomass. • Biotechnological strategies to improve large-scale production of stevia. [ABSTRACT FROM AUTHOR]

Plants produce many different specialized (secondary) metabolites that function in solving ecological challenges; few are known to function in growth or other primary processes. 17-Hydroxygeranylinalool diterpene glycosides (DTGs) are abundant herbivory-induced, structurally diverse and commonly malonylated defense metabolites in Nicotiana attenuata plants. By identifying and silencing a malonyltransferase, NaMaT1, involved in DTG malonylation, we found that DTG malonylation percentages are normally remarkably uniform, but when disrupted, result in DTG-dependent reduced floral style lengths, which in turn result from reduced stylar cell sizes, IAA contents, and YUC activity; phenotypes that could be restored by IAA supplementation or by silencing the DTG pathway. Moreover, the Nicotiana genus-specific JA-deficient short-style phenotype also results from alterations in DTG malonylation patterns. Decorations of plant specialized metabolites can be tuned to remarkably uniform levels, and this regulation plays a central but poorly understood role in controlling the development of specific plant parts, such as floral styles.

From the commercial extract of the leaves of Stevia rebaudiana Bertoni, a minor steviol glycoside, 13-[(2-O-β-D-glucopyranosyl-3-O-β-D-glucopyranosyl-β-D-glucopyranosyl)oxy] ent-kaur-16-en-19-oic acid-[(2-O-(3-O-β-D-glucopyranosyl-α-L-rhamnopyranosyl)-3-O-β-D-glucopyranosyl-β-D-glucopyranosyl) ester] (1); also known as rebaudioside O having seven sugar units has been isolated. Its structural characterization has been achieved by the extensive 1D (1H and 13C), and 2D NMR (COSY, HMQC, HMBC) as well as mass spectral data. Further, hydrolysis studies were performed on rebaudioside O using acid and enzymatic methods to identify aglycone and sugar residues in its structure as well as their configurations.

Five new diterpene glycosides, auricuosides I ( 1 ), II ( 2 ), III ( 3 ), IV ( 4 ), and V ( 5 ), a new flavonol glycoside, auricuoflavonoside I ( 6 ), and a new megastigmane glycoside, auricuomegastigmane I ( 7 ), were isolated from the seeds of Cassia auriculata , together with 11 known constituents. The chemical structures of seven new constituents were characterized on the basis of chemical and physicochemical evidence. In the present study, auricuosides I ( 1 )–V ( 5 ) were obtained from the seeds of C. auriculata . To the best of our knowledge, there is no report about the isolation of kaurenolides with hydroxy group at 14-position from plants. This finding is interesting from the perspective of chemotaxonomy and biosynthesis of kaurenolide. [ABSTRACT FROM AUTHOR]

From the commercial extract of the leaves of Stevia rebaudiana Bertoni, a minor steviol glycoside, 13-[(2-O-β-D-glucopyranosyl-3-O-β-D-glucopyranosyl-β-D-glucopyranosyl)oxy] ent-kaur-16-en-19-oic acid-[(2-O-(3-O-β-D-glucopyranosyl-α-L-rhamnopyranosyl)-3-O-β-D-glucopyranosyl-β-D-glucopyranosyl) ester] (1); also known as rebaudioside O having seven sugar units has been isolated. Its structural characterization has been achieved by the extensive 1D (1H and 13C), and 2D NMR (COSY, HMQC, HMBC) as well as mass spectral data. Further, hydrolysis studies were performed on rebaudioside O using acid and enzymatic methods to identify aglycone and sugar residues in its structure as well as their configurations. [ABSTRACT FROM AUTHOR]

Abstract: Phytochemical investigation on the whole plant of Anemone rivularis var. flore-minore led to the isolation of a new labdane-type diterpene glycoside (1) and a new trihydroxyfuranoid lignanoid glycoside (2), together with three known triterpene and triterpenoid glycosides (3–5). The structures of the two new compounds were elucidated as β-d-glucopyranosyl (13S)-13-hydroxy-7-oxo-labda-8,14-diene-18-oate (1) and (7S,7′R,8R,8′S)-7′-butoxy-7,9′-epoxy-4,4′,9-trihydroxy-3,3′-dimethoxylignane 9-O-β-d-glucopyranoside (2), on the basis of extensive spectral analysis and chemical evidence. Compound 1 is characterized by a glucose (Glc) esterified C-18 carboxyl group, which is a rarely encountered labdane-type diterpene glycoside in nature. The two new compounds (1 and 2) reported here are the first examples of diterpene glycoside and lignanoid glycoside found in the genus Anemone, and the known triterpene and triterpenoid glycosides (3–5) are identified for the first time from the title plant. [Copyright &y& Elsevier]

The article presents a review on the improvement of Stevia rebaudiana (Bertoni), a herbaceous perennial plant whose leaves produce diterpene glycosides, non-nutritive, non-toxic and high-potency sweeteners that can substitute for sucrose and synthetic sweeteners. Aside from its sweetening property, the plant also has medicinal uses and value. Its quality traits can reportedly be improved with the use of conventional plant breeding approaches including selection and intercrossing among genotypes.

Abstract: Steviol glycosides are found in high concentrations in the leaves of the Paraguayan perennial herb Stevia rebaudiana and their intense sweetness, as well as high concentration in Stevia leaf tissue, has made them the subject of research interest for over 100 years. Steviol glycosides are diterpenoids whose biosynthetic pathways share four steps in common with gibberellic acid formation. The convergence of genomics and plant biochemistry has led to the rapid elucidation of the genes coding for the various enzymes in the biosynthetic pathway. Functional characterization of the enzymes coded for by those genes is on-going. The first committed step in the pathway is the synthesis of the aglycone steviol and the various glycosides found in the leaf tissue result from the elaboration of steviol by a number of glucosyltransferases. [Copyright &y& Elsevier]

A new unusual kauranoid diterpene glycoside, named amygdaloside, was isolated from the nuts of almond (Prunus amygdalus). It''s structure was established as 17-O-β-D-glucopyranoside ent-6,7-epoxy-6-hydroxyl-6,7-secokaur-19-oic acid, 6,19-lactone 16β17-diol on the basis of high-resolution 1D and 2D NMR spectral studies. [Copyright &y& Elsevier]

Holothuria (Metriatyla) scabra Jaeger (H. scabra), sea cucumber, is the marine organism that has been used as traditional food and medicine to gain the health benefits since ancient time. Although our recent studies have shown that crude extracts from H. scabra exhibited neuroprotective effects against Parkinson's disease (PD), the underlying mechanisms and bioactive compounds are still unknown. In the present study, we examined the efficacy of purified compounds from H. scabra and their underlying mechanism on α-synuclein degradation and neuroprotection against α-synuclein-mediated neurodegeneration in a transgenic Caenorhabditis elegans PD model. The H. scabra compounds (HSEA-P1 and P2) were purified and examined for their toxicity and optimal dose-range by food-clearance and lifespan assays. The α-synuclein degradation and neuroprotection against α-synuclein-mediated neurodegeneration were determined using transgenic C. elegans model, P unc-54 ::α-syn and P dat-1 :: α-syn; P dat-1 ::GFP, respectively, and then further investigated by determining the behavioral assays including locomotion rate, basal slowing rate, ethanol avoidance, and area-restricted searching. The underlying mechanisms related to autophagy were clarified by quantitative PCR and RNAi experiments. Our results showed that HSEA-P1 and HSEA-P2 significantly diminished α-synuclein accumulation, improved motility deficits, and recovered the shortened lifespan. Moreover, HSEA-P1 and HSEA-P2 significantly protected dopaminergic neurons from α-synuclein toxicity and alleviated dopamine-associated behavioral deficits, i.e., basal slowing, ethanol avoidance, and area-restricted searching. HSEA-P1 and HSEA-P2 also up-regulated autophagy-related genes, including beclin-1/bec-1, lc-3/lgg-1 , and atg-7/atg-7. RNA interference (RNAi) of these genes in transgenic α-synuclein worms confirmed that lc-3/lgg-1 and atg-7/atg-7 were required for α-synuclein degradation and DAergic neuroprotection activities of HSEA-P1 and HSEA-P2. NMR and mass spectrometry analysis revealed that the HSEA-P1 and HSEA-P2 contained diterpene glycosides. These findings indicate that diterpene glycosides extracted from H. scabra decreases α-synuclein accumulation and protects α-synuclein-mediated DAergic neuronal loss and its toxicities via lgg-1 and atg-7. [Display omitted] [ABSTRACT FROM AUTHOR]

Poor aqueous solubility of some minor steviol glycosides (SGs) has prevented their potential widespread usage as non-nutritional high intensity sweeteners in beverage industry. Rebaudioside B (reb B) is one of the minor SGs found in stevia leaf, and has a better taste quality than many of the major SGs. However, reb B suffers from poor aqueous solubility and low dissolution rate, which greatly limits its application, especially in beverages. In our effort to enhance its solubility by using natural means, we discovered that under certain conditions reb B forms hemihydrate crystal, which has much lower solubility and dissolution rate than commercial powder reb B product. The crystal was characterized by Fourier Transform Infrared spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), and X-ray Diffraction (XRD). This may offer more insight into the interaction of SGs with water at molecular level, and therefore provide new guidance on current efforts to enhance the solubility of SGs. • Hemihydrate crystalline rebaudioside B was discovered for the first time. • FT-IR, SEM and XRD were used to characterize the hemihydrate rebaudioside B crystal. • The hemihydrate crystal has lower solubility than commercially available high purity rebaudioside B. • The finding provides more insight into the interaction of steviol glycoside and water at molecular level. [ABSTRACT FROM AUTHOR]