Flavonoids from Lupinus texensis and their free radical scavenging activity

Seventeen flavonoids including one new compound were isolated from Texas bluebonnet (Lupinus texensis), the state flower of Texas. Their structures were determined by extensive nuclear magnetic resonance and high-resolution electrospray ionization mass spectrometry analyses. High-performance liquid chromatography analytic method for simultaneous determination of the 17 compounds was established and validated. Eleven isolated flavonoids were first evaluated for their free radical scavenging activity using α,α-diphenyl-β-picrylhydrazyl scavenging assay and they showed activity with EC(50) 48.6-172.5 μg mL(-1).     

Polychromatic action spectrum for the induction of a mycosporine-like amino acid in a rice-field cyanobacterium, Anabaena sp

A polychromatic action spectrum for the induction of an ultraviolet-absorbing/screening mycosporine-like amino acid (MAA) has been determined in a filamentous and heterocystous nitrogen-fixing rice-field cyanobacterium, Anabaena sp. High-performance liquid chromatographic (HPLC) studies revealed the presence of only one type of MAA, which was identified as shinorine, a bisubstituted MAA containing both glycine and serine groups having a retention time at 2.8 min and an absorption maximum at 334 nm. Exposure of cultures to simulated solar radiation in combination with various cut-off filters (WG 280, 295, 305, 320, 335, 345, GG 400, 420, 455, 475, OG 515, 530, 570, RG 645, 665 and a broad-band filter, UG 11) clearly revealed that the induction of the MAA takes place only in the UV range. Photosynthetic active radiation (PAR) had no significant impact on MAA induction. The ratio of the absorption at 334 nm (shinorine) to 665 nm (chlorophyll a) and the action spectrum also showed the induction of MAA to be UV dependent peaking in the UV-B range at around 290 nm. The results indicate that the studied cyanobacterium, Anabaena sp. may protect itself from deleterious short wavelength solar radiation by its ability to synthesize a mycosporine-like amino acid in response to UV-B radiation and thereby screen the negative effects of UV-B.     

Flavanol derivatives from Rhizophora stylosa and their DPPH radical scavenging activity

A new acetylated flavanol, 3,7-O-diacetyl (-)-epicatechin (3), and seven known flavanol derivatives, (-)-epicatechin (1), 3-O-acetyl (-)-epicatechin (2), 3,3',4',5,7-O-pentaacetyl (-)-epicatechin (4), (+)-afzelechin (5), (+)-catechin (6), cinchonain Ib (7), and proanthocyanidin B2 (8), were isolated from the stems and twigs of the mangrove plant Rhizophora stylosa and identified. The crude extract, the different fractions and all of the purified compounds were evaluated for DPPH radical scavenging activity.     

Chemical constituents of two sages with free radical scavenging activity

From the aerial parts of Salvia trichoclada Bentham and S. verticillata L. one new and two known phenolic acids, 3-(3',4'-dihydroxyphenyl)-2-hydroxymethyl propionic acid (1), 3-(3',4'-dihydroxyphenyl) lactic acid (2), and rosmarinic acid (3); two flavonoids, apigenin 4'-methyl ether 7-O-glucuronide (4), and luteolin 7-O-beta glucuronide (5); two lupan type triterpene aglycones, lupeol (6), and 30-hydroxylup-20 (29)-en-3-on (7); an oleanane-type triterpene acid, oleanolic acid (8); and an ursan-type triterpene acid, ursolic acid (9) were isolated. The structures of the compounds were elucidated by spectroscopic analysis. Different extracts of the plants were examined for their free radical scavenging activities by DPPH (2,2-Diphenyl-1-picrylhydrazyl) assay. Some of the polar extracts showed high free radical scavenging activity.     

Kinetics of the radical scavenging activity of beta-carotene-related compounds

To clarify the non-enzymatic radical-scavenging activity of beta-carotene-related compounds and other polyenes, we used differential scanning calorimetry to study the kinetics of radical polymerization of methyl methacrylate (MMA) by 2,2'-azobisisobutyronitrile (AIBN) or benzoyl peroxide (BPO) in the absence or presence of polyenes under nearly anaerobic conditions at 70 degrees C, and analyzed the results with an SAR approach. The polyenes studied were all-trans retinol, retinol palmitate, calciferol, beta-carotene and lycopene. Polyenes produced a small induction period. The stoichiometric factor (n) (i.e. the number of radicals trapped by each inhibitor molecule) of polyenes was close to 0. Tetraterpenes (beta-carotene, lycopene) suppressed significantly more of the initial rate of polymerization (R(inh)) than did diterpenes (retinol, retinol palmitate). The inhibition rate constants (k(inh)) for the reaction of beta-carotene with AIBN- or BPO-derived radicals were determined to be 1.2-1.6x10(5) l/mol s, similar to published values. A linear relationship between (k(inh)) and the kinetic chain length (KCL) for polyenes was observed; as (k(inh)) increased, KCL decreased. KCL also decreased significantly as the number of conjugated double bonds in the polyenes increased. Polyenes, particularly beta-carotene and lycopene, acted as interceptors of growing poly-MMA radicals.     

Ozone enhanced production of potentially useful exopolymers from the cyanobacterium Nostoc muscorum

Extracellular polysaccharides (EPS) from Nostoc muscorum, a heterocystous, filamentous cyanobacterium isolated from a jhumland (shifting cultivation) soil of Assam, North-East India, was physico-chemically characterized to find out its potential applications and to improve its production with some stress source like ozone. Using Response Surface Methodology (RSM), EPS production was improved. Accordingly, with magnesium sulfate (MgSO_4·7H₂O) at 62 mg L⁻¹, Sodium Chloride (NaCl) at 58 mg L⁻¹ and 56 mg L⁻¹ di-potassium hydrogen phosphate (K₂HPO₄), a yield of 126.73 μg mL⁻¹ of EPS in 12 days was obtained which was four-fold higher than un-optimised control. An important finding of this study is that EPS production could be further enhanced by over 50% with a mild stress by a strong oxidizing agent ozone (O₃). Physico-chemical properties of this Ozone induced EPS was evaluated and found identical to uninduced EPS. EPS was composed of the hexoses- Glucose (14.80%), Galactose (18.01%) and Mannose (12.64%), the pentoses- Arabinose (17.86%) and Xylose (11.66%), the deoxyhexose- Fucose (12.53%) and Rhamnose (12.50%). Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) analysis revealed the presence of the functional groups uronic acid and traces of sulfate group. The Zeta potential analysis revealed that the emulsions were stabilized electrosterically rather than by pure electrostatic repulsion and steric stabilization. EPS at 1% in hydrocarbons and vegetable oils was observed to be an excellent emulsifier (99%), with reasonable stability. Rheological study revealed that the EPS (1%) was a non- Newtonian weak gel, useful for emulsification activity. Unlike petroleum-based emulsifiers now in use, bio-based EPS are renewable, economical and eco-friendly. The physico-chemical characteristics suggest their utility in a wide variety of other applications including bioremediation, manufacture of paints, shear reduction in oil drilling etc.     

Characteristics of the OH radical scavenging activity of tea catechins

Reaction rate constants of (−)-epigallocatechin gallate (EGCG) and (+)-catechin with the hydroxyl radical (·OH) were measured using the rapid flow ESR method. The rate constant of EGCG was larger twice than that of the pyrogallol or gallic acid, they are the model compounds of the B ring of EGCG. It was explained by the quantum-chemical calculation of the bond dissociation energy (BDE) of the phenolic hydroxyl group (ϕ-OH) and the spin densities of EGCG radical. The energy of the EGCG radical was lowered by the hydrogen bonding between the radical part on the B ring and the hydroxyl group on the gallate group, leading to the lowering of BDE. Linear relationship between the relative activation energy and BDE of all the polyphenols measured was observed (Evans-Polanyi equation), showing that the reaction with ·OH occurs in the same manner.     

Dihydrochalcones with radical scavenging properties from the leaves of Syzygium jambos

Chemical investigation of the dichloromethane extract of the leaves of Syzygium jambos furnished three dihydrochalcones, phloretin 4'-O-methyl ether (2',6'-dihydroxy-4'-methoxydihydrochalcone) (1), myrigalone G (2',6'-dihydroxy-4'-methoxy-3'-methyldihydrochalcone) (2), and myrigalone B (2',6'-dihydroxy-4'-methoxy-3,5'-dimethyldihydrochalcone) (3) with radical scavenging properties towards the DPPH radical by spectrophotometric method.     

Daily variation in cellular content of UV-absorbing compounds mycosporine-like amino acids in the marine dinoflagellate Scrippsiella sweeneyae

Sudden exposure experiments to high PAR (photosynthetically available radiation) or high PAR+UVR (ultraviolet radiation) were conducted for the marine dinoflagellate Scrippsiella sweeneyae acclimated to either low PAR or high PAR to determine the induction of cellular mycosporine-like amino acid (MAA) in relation to photosynthesis status. When the exposure to high PAR (30.8 Wm(-2)) was provided at different time in the light period for S. sweeneyae acclimated to low PAR (7.7 Wm(-2)) which suppressed photosynthesis, S. sweeneyae could enhance the induction of MAA but it only occurred in the first half of the light period. When UVR exposure was provided for the culture acclimated to high PAR which enhanced photosynthesis, cellular MAA content did not increase during the entire light period, but displayed daily variation similar to the control for two and half days. Daily variation of cellular MAA content did not synchronized with that of cell volume and cellular chlorophyll a content. The individual MAAs also revealed similar daily variations with different phase, which increased for a few hours in the beginning of the light period, except for cellular palythine content. Thus the total cellular MAA content revealed daily variation with changing the relative composition within a few hours. As one of the biological protective strategies against harmful UVR in sunlight, the daily vertical migration in the bloom forming dinoflagellates might be accompanied by the daily variation of cellular MAA content for a photosynthesis at daytime.     

Use of N-protected amino acids in the Minisci radical alkylation

[reaction: see text] The Minisci radical alkylation has been demonstrated on a range of commercially available glycine derivatives and proceeds in good to high yield. When extending the reaction to other amino acids, competitive oxidation of the initially formed radical was overcome by using the phthalimide protecting group.     

An electrochemical method for quantification of the radical scavenging activity of SOD

An electrochemical technique for the determination of enzymatic superoxide scavenging activity is described. In amperometric mode of sensor operation ¶the oxidation current was altered by additions of superoxide dismutase (SOD). The 50% inhibition value (I50) corresponded to 0.165 U of the standard photometric test of McCord and Fridovich. Influence by inert proteins was much less than in the standard method: The SOD/BSA ratio was 4 × 10⁵. Potentially interfering substances, e.g. ascorbic acid and glutathione, were tested. Plasma samples of rats which were treated with modified SOD during cerebral ischaemia, were assayed with the new method and the standard photometric test. A good correlation was found for the analysis in these physiological samples (r = 0.97).     

An electrochemical method for quantification of the radical scavenging activity of SOD

An electrochemical technique for the determination of enzymatic superoxide scavenging activity is described. In amperometric mode of sensor operation ?the oxidation current was altered by additions of superoxide dismutase (SOD). The 50% inhibition value (I50) corresponded to 0.165 U of the standard photometric test of McCord and Fridovich. Influence by inert proteins was much less than in the standard method: The SOD/BSA ratio was 4 × 10⁵. Potentially interfering substances, e.g. ascorbic acid and glutathione, were tested. Plasma samples of rats which were treated with modified SOD during cerebral ischaemia, were assayed with the new method and the standard photometric test. A good correlation was found for the analysis in these physiological samples (r = 0.97). Received: 3 February 1999 / Revised: 17 May 1999 / Accepted: 19 May 1999     

In vitro cis-trans photoisomerization of palythene and usujirene. Implications on the in vivo transformation of mycosporine-like amino acids

The in vitro photoinduced reactions of the mycosporine-like amino acids (MAA) usujirene and palythene were studied by monochromatic stationary irradiation at 366 nm. High-performance liquid chromatography analysis of the irradiated aqueous solution of usujirene indicated a low photoreactivity on the basis of the observed photodecomposition quantum yield of phi(-U) = (2.86 +/- 0.80) x 10(-5), which can be partially accounted for by the cis-trans photoisomerization of usujirene to palythene (phi(U-->P) = [1.71 +/- 0.13] x 10(-5)). However, palythene in aqueous solution showed a higher photostability than did usujirene under equivalent conditions, establishing a photostationary mixture of cis-trans isomers with a relative composition of palythene-usujirene (11:1). These results may explain the preferential in vivo accumulation of palythene relative to that of usujirene observed in several dinoflagellate species.     

Iridoid glycosides from Phlomis likiangensis with free-radical scavenging activity

Phytochemical investigation of an extract of the aerial and underground parts of Phlomis likiangensis resulted in the identification of five new iridoid glycosides, namely as 5,9-epi-6-methoxy-7,8-dehydropenstemonoside (1), 6-methoxy-7,8-dehydropenstemonoside (2), 6-methoxy-7,8-dehydropenstemoside (3), 6-ethoxy-7,8-dehydropenstemoside (4), and phloloside G (5). On the basis of a combination of spectroscopic data and acid hydrolysis, their structures were determined. The free-radical scavenging activity of these compounds was assessed using the DPPH and ABTS assays.     

Synthesis and radical ring‐opening polymerization of vinylcyclopropanes derived from amino acids with hydrophobic moieties

Six 1,1‐disubstituted vinylcyclopropanes (VCP) were synthesized from glycine and amino acids bearing hydrophobic moieties, l ‐alanine, l ‐valine, l ‐leucine, l ‐isoleucine, and l ‐phenylalanine. These VCP derivatives efficiently underwent radical ring‐opening polymerization to afford the corresponding polymers bearing trans‐vinylene moiety in the main chains and the amino acid‐derived chiral moieties in the side chains. The polymers were film‐formable, and in the films of polymers bearing the glycine‐ and alanine‐derived side chains, presence of hydrogen bonding was confirmed by IR analysis. Thermogravimetric analysis of the polymers revealed that the temperatures of 5% weight loss were higher than 300 °C. Differential scanning calorimetry clarified that the polymers were amorphous ones showing glass transition temperatures in a range of 48–80 °C. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3996–4002     

A DFT study on the radical scavenging activity of juglone and its derivatives

The structural and electronic properties of juglone and its derivatives and their radicals were investigated at density functional level. The topology of electron density and the hydrogen bond properties of the studied structures were investigated using the Atoms in Molecules (AIM) theory. It turned out that the presence of the dihydroxy functionality increases the radical stability through hydrogen bond formation and favors hydrogen atom abstraction. The introduction of electron-donating groups for the molecules increases the activities of antioxidants. Moreover, juglone and its derivatives appear to be good candidates for the one-electron-transfer mechanism. Their planar conformation and the extended electronic delocalization between adjacent rings determine low ionization potential (IP) values, and it can be further improved by the introduction of the electron-donating groups for the molecules.