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A new schiartane-type nortriterpenoid, micrandilactone H was isolated from Kadsura longipedunculata Finet et Gagnep. Its 2D (two dimension) structure was elucidated by NMR spectroscopic analysis, and it is similar to that of Kadnanolactones H and the absolute configuration was established through X-ray diffraction and ECD data analysis. This represents the first complete assignment of the absolute configuration of a schiartane-type nortriterpenoid by X-ray diffraction and the ECD method. Micrandilactone H showed moderate hepatoprotective activity against N-acetyl-p-aminophenol (APAP)-induced toxicity in HepG2 cells with cell survival rates of 56.84% at 10 μM. [ABSTRACT FROM AUTHOR]

Abstract: Circular dichroism is a powerful tool for establishing the absolute configuration of flavonoids and proanthocyanidin analogues. It has been utilized to study the configuration of flavanones, dihydroflavonols (3-hydroxyflavanones), flavan-3-ols, flavan-4-ols, flavan-3,4-diols, flavans, isoflavans, isoflavanones, pterocarpans, 6a-hydroxypterocarpans, rotenoids, 12a-hydroxyrotenoids, neoflavonoids, 3,4-dihydro-4-arylcoumarins, 4-arylflavan-3-ols, auronols, homoisoflavanones, proanthocyanidins, and various classes of biflavonoids. Results relevant to the correlation of circular dichroic data and the absolute configuration of the diastereoisomers of some of the above classes of compounds will be discussed. [Copyright &y& Elsevier]

[Display omitted] • The leuconoxine-type diazaspiroindole alkaloids 1 and 2 were isolated from Cryptolepis dubia. • The absolute configurations of 1 and 2 were defined by ECD calculations. • Compounds 1 and 2 exhibited selective cytotoxicity against human cancer cells. Two leuconoxine-type diazaspiroindole alkaloids, the known compound, (+)-melodinine E (1), and its new analogue, (+)-11-chloromelodinine E (2), were isolated from the stems of Cryptolepis dubia (Burm.f.) M.R. Almeida (Apocynaceae), collected in Laos. The chemical structures of these compounds were determined by analysis of their spectroscopic data and by comparison of these data with literature values, of which the molecular structure of 1 has been determined previously by analysis of its single-crystal X-ray diffraction data. The absolute configurations of 1 and 2 have been defined by their experimental and simulated electronic circular dichroism (ECD) spectroscopic data and supported by 1H and 13C NMR-based DP4+ probability analysis and specific rotation calculations. When tested against a small panel of human cancer cell lines, these two compounds exhibited selective cytotoxicity toward OVCAR3 human ovarian cancer cells. [ABSTRACT FROM AUTHOR]

Often, chiral natural products exist as single stereoisomers; however, simultaneous occurrences of both enantiomers can exist in nature, resulting in scalemic or racemic mixtures. Ascertaining theabsolute configuration (AC) of natural products is pivotal for attributing their specific biological signature. Specific rotation data commonly characterize chiral non-racemic natural products; however, measurement conditions, viz., solvent and concentration, can influence the sign of specific rotation values, especially when characterizing natural products possessing small values. For example, licochalcone L, a minor constituent of Glycyrrhiza inflata , was reported with a specific rotation of [ α ] D 22 = +13 (c 0.1, CHCl 3); however, not establishing the AC and the reported zero specific rotation for an identical compound, licochalcone AF1, resulted in debatable chirality and its biogenesis. In this study, a combined experimental and computational chiroptical approach involving specific rotation and electronic circular dichroism (ECD) data, supported by time-dependent density functional theory (TDDFT), were effectively utilized to establish the AC of licochalcone L as the (E , 2″ S)-isomer. Establishing the 2″ S absolute configuration permitted the conception of a reasonable biosynthetic pathway involving intramolecular '5-exo-tet' ring opening of a chiral oxirane to form chiral licochalcone L in G. inflata. [Display omitted] • Chirality of natural products is key to their biological activity. • Licochalcone L is a minor constituent of G. inflata , with a reported specific rotation but the absolute configuration is unknown. • Solvent-specific geometrical isomerism was observed with licochalcone L. • The absolute stereostructure of licochalcone L was unequivocally established as E , 2″ S. [ABSTRACT FROM AUTHOR]

Abstract: Morusalbanol A (1), a neuro-protective Diels–Alder adduct with a new carbon skeleton, was isolated from the bark of Morus alba. Compound 1 showed evidence of interesting astropisomerism, and resulted in the absence of a number of key proton and carbon signals in the NMR spectra. Its structure was thus elucidated by spectroscopic analysis of its peracetylated derivative (2) and its absolute configuration established as 1S,3S,4R,5S via experimental and calculated ECD spectra of 1. In a neuro-protective assay, morusalbanol A (1) significantly attenuated the H2O2-induced cell damage in a dose-dependent manner. [Copyright &y& Elsevier]

Abstract: A new fascaplysin analogue, 3-bromohomofascaplysin A (1), along with two known analogues, homofascaplysin A (2) and fascaplysin (3), were isolated from a Fijian Didemnum sp. ascidian. The absolute configurations of 3-bromohomofascaplysin A (1) and homofascaplysin A (2) were determined via experimental and theoretically calculated ECD spectra. The differential activities of 1–3 against different blood-borne life stages of the malaria pathogen Plasmodium falciparum were assessed. Homofascaplysin A (2) displayed an IC50 of 0.55±0.11nM against ring stage parasites and 105±38nM against all live parasites. Given the stronger resistance of ring stage parasites against most current antimalarials relative to the other blood stages, homofascaplysin A (2) represents a promising agent for treatment of drug resistant malaria. [Copyright &y& Elsevier]

The absolute configurations of three flavanone-(3→8″)-flavone type biflavonoids, (+)-morelloflavone (1), (+)-morelloflavone-7-sulfate (2) and (+)-volkensiflavone-7-sulfate (3) isolated from Rheedia acuminata were confirmed by circular dichroism as 2R,3S, hence clarifying the literature confusion of 2S,3R absolute configuration for (+)-morelloflavone. The conformations of this class of biflavonoids were studied for the first time by variable temperature NMR, NOESY, and computational calculations using a semi-empirical AM1 method. The coexistence of two conformers for morelloflavone (1) in solution at room temperature was confirmed by variable temperature NMR experiments. NOESY and computational calculations indicated that in the major and minor conformers 1a and 1b, respectively, the flavone DEF moiety is extended above and below the plane of the A/C-ring of the flavanone ABC unit, respectively. The C-3 proton of the C-ring of morelloflavone (1) is exchangeable by deuterium in acetone-d6/D2O at ambient temperature with retention of configuration, indicating considerable chiral stability of this class of biflavonoids. [Copyright &y& Elsevier]