Enantiomers of an Indole Alkaloid Containing Unusual Dihydrothiopyran and 1,2,4-Thiadiazole Rings from the Root of Isatis indigotica

Three pairs of alkaloid enantiomers from the root of Isatis indigotica

Three pairs of enantiomerically pure alkaloids with diverse structure features, named isatindigoticoic acid A and epiisatindigoticoic acid A [(−)-1 and (+)-1], phaitanthrin A and epiphaitanthrin A [(−)-2 and (+)-2], and isatindopyrromizol A and epiisatindopyrromizol A [(−)-3 and (+)-3], respectively, were isolated from an aqueous extract of the roots of Isatis indigotica. Racemic and scalemic mixtures of these enantiomers were separated by HPLC on a chiral semi-preparative column. Their structures including absolute configurations were determined by extensive spectroscopic analysis in conjunction with the calculation of electronic circular dichroism (ECD) spectra. The enantiomer pairs possess parent structures of 2-oxo-1,2,3,4-tetrahydroquinoline-4-carboxylic acid, indolo[2,1-b]quinazolinone, and 3-thioxohexahydro-1H-pyrrolo[1,2-c]imidazol-1-one, respectively. Except for phaitanthrin A [(−)-2] which the configuration was previously undetermined, these compounds are new enantiomeric natural products.

Indole alkaloid glucosides from the roots of Isatis indigotica

Five new indole alkaloid glucosides named isatindigotindolosides A-E (1-5), along with three known analogs (6-8), were isolated from an aqueous extract of the Isatis indigotica roots. Their structures including the absolute configurations were determined based on comprehensive spectroscopic data analysis, combined with chemical methods and electronic circular dichroism spectra calculations. In the preliminary assays, compounds 1, 6 and 7 showed antiviral activity against influenza virus A/Hanfang/359/95 (H3N2) with IC50 values of 14.6-33.3 μM. Compound 1 also exhibited inhibitory effect against nitric oxide (NO) production in microglial cell BV2 with an inhibition ratio of 93.0% at 10 μM.

Sesquiterpene glycosides from the roots of Codonopsis pilosula

Three new sesquiterpene glycosides, named codonopsesquilosides A−C (1−3), were isolated from an aqueous extract of the dried roots of Codonopsis pilosula. Their structures including absolute configurations were determined by spectroscopic and chemical methods. These glycosides are categorized as C₁₅ carotenoid (1), gymnomitrane (2), and eudesmane (3) types of sesquiterpenoids, respectively. Compound 1 is the first diglycoside of C₁₅ carotenoids to be reported. Compound 2 represents the second reported example of gymnomitrane-type sesquiterpenoids from higher plants. The absolute configurations were supported by comparison of the experimental circular dichroism (CD) spectra with the calculated electronic CD (ECD) spectra of 1−3, their aglycones, and model compounds based on quantum-mechanical time-dependent density functional theory. The influences of the glycosyls on the calculated ECD spectra of the glycosidic sesquiterpenoids, as well as some nomenclature and descriptive problems with gymnomitrane-type sesquiterpenoids are discussed.

Synthesis of the 1,2,4-thiadiazole alkaloids polycarpathiamines A and B

Synthesis of the 1,2,4-thiadiazole alkaloids polycarpathiamines A and B is described. The heteroaromatic core of the natural products was assembled using a one-pot benzylic oxidation–oxidative heterocyclization process.

C14-polyacetylenol glycosides from the roots of Codonopsis pilosula

Eight new C14-polyacetylenol glycosides, containing ene-diyne and ene-yn-ene chromophores named codonopilodiynosides H-M (1-6) and codonopiloenynenosides A and B (7 and 8), respectively, together with three known analogs lobetyolinin, pratialin B, and lobetyolin (9-11), were isolated from an aqueous extract of the roots of Codonopsis pilosula. Their structures were determined by spectroscopic and chemical methods including 2D NMR data analysis and enzymatic hydrolysis. The absolute configurations of aglycones in 1-10 were assigned by application of the methoxyphenylacetic acid (MPA) determination rule of Δδ(RS) values and/or the empirical rule of Mo2(OAc)4-induced circular dichroism for the vicinal diols, or by comparison of specific rotation values with those of reported compounds. Compounds 4-6 are the first polyacetylenol glycosides possessing a cis-ene-diyne chromophore from the genus Codonopsis, while 8 has a rear trans-ene-yn-cis-ene chromophore and a (6S,7S)-6,7-diol unit against a (6R,7R)-6,7-diol unit in the others. The absolute configurations of lobetyolinin (9) and pratialin B (10) were determined for the first time.

Isolation and bioactivity of diterpenoids from the roots of Salvia grandifolia

A phytochemical investigation of root extracts of Salvia grandifolia led to isolation of six previously unreported diterpenoids, grandifolias A-F, along with eight known compounds. The structures of grandifolias A-F were primarily established by extensive 1D and 2D NMR spectroscopic analyses, as well as HRESIMS data. Their absolute configurations were assigned by their calculated and experimental electronic circular dichroism spectra or by X-ray diffraction analysis. All of the diterpenoids were evaluated for their vasorelaxant effects. Grandifolia B and isograndifoliol both exhibited dose-dependent vasorelaxant effects on rat aortic rings, preconstricted by KCl or norepinephrine, with EC50 values of 36.36-74.51μg/mL.

4-Hydroxybenzyl-substituted amino acid derivatives from Gastrodia elata

Seven new 4-hydroxybenzyl-substituted amino acid derivatives (1−7), together with 11 known compounds, were isolated from an aqueous extract of the rhizomes of Gastrodia elata Blume. Their structures were determined by spectroscopic and chemical methods. Compounds 1−3 are pyroglutamate derivatives containing 4-hydroxybenzyl units at the N atom and 4−7 are the first examples of natural products with the 4-hydroxybenzyl unit linked via a thioether bond to 2-hydroxy-3-mercaptopropanoic acid (4−6) and 2-hydroxy-4-mercaptobutanoic acid (7), which would be biogenetically derived from cysteine and homocysteine, respectively. The structures of 1 and 2 were verified by synthesis, while the absolute configurations of 4, 5 and 7 were assigned using Mosher’s method based on the MPA determination rule of Δδ_RS values. The known compound 4-(hydroxymethyl)-5-nitrobenzene-1,2-diol (8) exhibited activity against Fe²⁺-cysteine induced rat liver microsomal lipid peroxidation with IC₅₀ values of 9.99×10⁻⁶ mol/L.

A New Metabolite with a Unique 4-Pyranone-γ-Lactam-1,4-Thiazine Moiety from a Hawaiian-Plant Associated Fungus

An endophytic fungus Paraphaeosphaeria neglecta FT462 isolated from the Hawaiian-plant Lycopodiella cernua (L.) Pic. Serm produced one unusual compound (1, paraphaeosphaeride A) with the 4-pyranone-γ-lactam-1,4-thiazine moiety, along with two new compounds (2 and 3, paraphaeosphaerides B and C, respectively) and the known compound (4). Compounds 1-3 were characterized by NMR and MS spectroscopic analysis. The absolute configuration of the 3-position of compound 1 was determined as S by electronic circular dichroism (ECD) calculations. Compound 3 also showed STAT3 inhibition at 10 μM.

C₁₄-polyacetylene glucosides from Codonopsis pilosula

Seven new C14-polyacetylene glucosides codonopilodiynosides A-G (1-7) were isolated from an aqueous extract of the Codonopsis pilosula roots. Their structures were determined by spectroscopic and chemical methods as (-)-(5S,6E,12E)-tetradeca-6,12-dien-8,10-diyn-1,5,14-triol 5-O-β-D-glucopyranoside (1), (-)-(5S,6E,12E)-tetradeca-6,12-dien-8,10-diyn-1,5,14-triol 5-O-β-D-glucopyranosyl-(1″ → 2')-β-D-glucopyranoside (2), (-)-(5S,6E,12E)-tetradeca-6,12-dien-8,10-diyn-1,5,14-triol 5,14-di-O-β-D-glucopyranoside (3), (-)-(5S,6E)-tetradeca-6-en-8,10-diyn-1,5,14-triol 5-O-β-D-glucopyranoside (4), (-)-(5S,6E,12E)-tetradeca-6,12-dien-8,10-diyn-1,5-diol 5-O-β-D-glucopyranosyl-(1″ → 2')-β-D-glucopyranoside (5), (-)-(6S,4E,12E)-tetradeca-4,12-dien-8,10-diyn-1,6-diol 6-O-β-D-glucopyranosyl-(1″ → 2')-β-D-glucopyranoside (6), and (-)-(5S,6E)-tetradeca-6-en-1,5-epoxy-8,10-diyn-14-ol 14-O-β-D-glucopyranosyl-(1″ → 2')-β-D-glucopyranoside (7), respectively. The absolute configurations of 1-7 were assigned by enzymatic hydrolysis followed by isolation of glucose and aglycones (1a and 4a-7a), and subsequent comparison of specific rotation, TLC, and (1)H NMR data of the glucose with an authentic sugar sample and application of modified Mosher's method based on the MPA determination rule of Δδ(RS) values for 1a and 4a, and Δδ(S) values for 6a. The configuration of 7 was assigned by electronic circular dichroism calculations based on the quantum-mechanical time-dependent density functional theory.

Acetylenes and fatty acids from Codonopsis pilosula

Four new acetylenes (1–4) and one new unsaturated ω-hydroxy fatty acid (5), together with 5 known analogues, were isolated from an aqueous extract of Codonopsis pilosula roots. Their structures were determined by spectroscopic and chemical methods. The new acetylenes are categorized as an unusual cyclotetradecatrienynone (1), tetradecenynetriol (2), and rare octenynoic acids (3 and 4), respectively, and 3 and 4 are possibly derived from oxidative metabolic degradation of 1 and/or 2. The absolute configuration of 1 was assigned by comparison of the experimental circular dichroism (CD) spectrum with the calculated electronic circular dichroism (ECD) spectra of stereoisomers based on the quantum-mechanical time-dependent density functional theory, while the configuration of 2 was assigned by using modified Mosher׳s method based on the MPA determination rule of Δδ_RS values for diols.

Antiviral glycosidic bisindole alkaloids from the roots of Isatis indigotica

Seven new glycosidic bisindole alkaloids, isatindigobisindolosides A-G (1-7), were isolated from an aqueous extract of the Isatis indigotica roots. Their structures including absolute configurations were determined by spectroscopic and chemical methods, together with calculations of electronic circular dichroism (ECD) spectra based on the quantum-mechanical time-dependent density functional theory. In the NMR spectra of 1-3, it is found that integration of H-2 and intensity of C-2 are affected not only by a substitution group at C-2 but also by solvents. Influences of the glucopyranosyloxy on the calculated ECD spectra of the glycosidic bisindole alkaloids are discussed. Compounds 2, 5, and 6 showed antiviral activity against both the influenza virus A/Hanfang/359/95 (H3N2) and Coxsackie virus B3 with IC50 values of 8.4-100.0 μM.

Simple indole alkaloids and those with a nonrearranged monoterpenoid unit

This review summarizes the isolation, structure determination, total syntheses and biological activities of simple indole alkaloids and those with a nonrearranged monoterpenoid unit, with literature coverage from 2012 to 2013.

Research progress of Chinese herbal medicine Radix isatidis (banlangen)

Radix isatidis (R. isatidis) (Banlangen) is a traditional Chinese medicine (TCM) famous for its broad antiviral activity. Its clinical medical history spans several thousands of years in China. Many scientists and scholars have conducted systematic research on this herb from its pharmacognosy to pharmaceuticals, especially in China. Through our research and literature reports, we inferred that the antiviral activity of R. isatidis mostly depended on the water-soluble part, including amino acids, IRPS, nucleosides, and sulfur-containing alkaloids. By playing a role in directly killing pathogenic viruses or regulating the immune system to enhance anti-virus ability, R. isatidis's biological activities mostly depend on the synergistic effect of its multiple components. This article aims to expand understanding of R. isatidis in the following aspects including medicinal resources, chemical constituents, pharmacological activities, clinical applications, and separation and analytical technologies.

New cytotoxic 1,2,4-thiadiazole alkaloids from the ascidian Polycarpa aurata

Two new alkaloids, polycarpathiamines A and B (1 and 2), were isolated from the ascidian Polycarpa aurata. Their structures were unambiguously determined by 1D, 2D NMR, and HRESIMS measurements and further confirmed by comparison with a closely related analogue, 3-dimethylamino-5-benzoyl-1,2,4-thiadiazole (4), that was prepared by chemical synthesis. Compounds 1 and 2 both feature an uncommon 1,2,4-thiadiazole ring whose biosynthetic origin is proposed. Compound 1 showed significant cytotoxic activity against L5178Y murine lymphoma cells (IC50 0.41 μM).