María Isabel Chávez

Structural modification of eucalypt pulp lignin in a totally chlorine-free bleaching sequence including a laccase-mediator stage

Abstract Structural modification of eucalypt pulp lignin was investigated in a totally chlorine-free (TCF) bleaching sequence including a laccase-mediator stage. This stage was applied after two oxygen delignification stages, and was followed by an alkaline peroxide stage. After two oxygen delignification stages, two more stages with a laccase mediator and alkaline peroxide were applied. The residual lignins were enzymatically isolated from the different pulps and analyzed by spectroscopic techniques and analytical pyrolysis. The latter revealed high amounts of syringyl units (>70%) in the lignins. 13C-1H heteronuclear single quantum correlation (HSQC) NMR indicated high amounts of β-O-4′ inter-unit linkages (>75% side-chains). Changes in lignin composition and inter-unit linkages were demonstrated in the course of the bleaching sequence. Moreover, oxidative modification of the major syringyl units was shown by C2,6-H2,6 HSQC correlations and by the presence of oxidized pyrolysis markers in pyrograms. The existence of both Cα keto and carboxyl groups in the residual lignin, together with normal (Cα-hydroxylated) units, was revealed by heteronuclear multiple bond correlation (HMBC) between aromatic H2,6 and side-chain carbons. These Cα-oxidized structures represent nearly 60% of total units in the lignin isolated from the enzymatically treated pulp. Analysis of residual lignin after the final peroxide stage compared with a simple alkaline treatment revealed that most of the oxidatively altered lignin was removed by the alkali used in the peroxide stage. Thus, the kappa number decreased and the final residual lignin was more structurally related to that found before the oxidative stages, although it contained less resinols and more carboxyl group-bearing units. However, the action of peroxide is necessary to attain the high brightness required (>90% ISO).

Biflavonoids Isolated from Selaginella lepidophylla Inhibit Photosynthesis in Spinach Chloroplasts

Through bioactivity-guided chemical analysis of Selaginella lepidophylla, biflavonoids robustaflavone (1), 2,3-dihydrorobustaflavone (2), and 2,3-dihydrorobustaflavone-5-methyl ether (3) were isolated and their structures confirmed by spectroscopic and spectrometric analyses. Their NMR resonances were unambiguously assigned from HMBC, NOESY, and NOESY-1D experiments, and absolute configurations of 2 and 3 were established. Compound 3 has not been reported, and although structure of 2 was described before, the (13)C NMR assignment does not correlate with the structure reported. Therefore, this is the first report of 2. All compounds inhibited ATP production. Compounds 1 and 2 behaved as Hill reaction inhibitors. 1 interacted with photosystem II, transforming the reaction centers to silent centers at 300 and 600 microM. The interaction and inhibition target of 2 was located on Cyt b6f to PC. The three compounds also behaved as energy transfer inhibitors, 3 being the most active.

1H and DOSY NMR spectroscopy analysis of Ligusticum porteri rhizome extracts

The presence of dimeric phthalides and other constituents in extracts of the vegetal species Ligusticum porteri was established by NMR spectroscopy. In comparative qualitative 1H NMR analyses of acetone extracts of rhizomes from fresh and dried L. porteri samples, we found that the dimeric phthalides tokinolide B (3), diligustilide (4) and riligustilide (5) were naturally produced by the plant and not post‐harvest products. We also obtained DOSY 1H NMR data that provided both virtual separation and structural information for the phthalides present in a dry acetone extract of L. porteri. In addition, we developed a protocol for the quantification of dimeric phthalides, which is performed by calculating the relative ratio of the peak area of selected proton signals for some compounds with respect to the known signal of the internal standard, 4‐dimethylaminopyridine. The protocol allows the rapid and direct quantification of dimeric phthalides and others constituents in fresh L. porteri rhizomes. Copyright

ABIETANOID ACID FROM LEPECHINIA-CAULESCENS

Abstract The aerial parts of Lepechinia caulescens provided the new diterpene 7β-hydroxy-abietan-8(14)-en-18-oic acid 9α,13α-endoperoxide which decomposes to 7β-hydroxy-8α,9α,13α,14α-diepoxy-abietan-18-oic acid. Several known acids and flavonoids were also isolated from this species.

Effect of a serine-to-aspartate replacement on the recognition of chitin oligosaccharides by truncated hevein. A 3D view by using NMR

The interaction of a synthetically prepared mutant peptide of hevein (a well known chitin-binding lectin) Hev32S19D with chitin oligosaccharides (and chitosan analogues) has allowed us to estimate their affinity constants and associated thermodynamic data. The mutant peptide is able to bind chitin oligomers, but with significant decreases in the association constants with chito-oligosaccharides. The determination of the three-dimensional structure of the peptide mutant, by using NMR, has permitted us to deduce that the topology of the backbone is very similar to that of the parent Hev32 peptide. The same is true regarding the orientations of the key aromatic residues Trp21, Trp23, and Tyr30. The decrease in the association constants can be attributed to the different topological orientation of key side chains and to the importance of protein-sugar intermolecular essential hydrogen bonds and CH-pi stacking interactions. The analysis has permitted us to infer the free energy of binding associated with these interactions as well as to estimate the corresponding binding enthalpy.

Isolation and relay synthesis of 11α-hydroperoxy diacetyl hederagenin, a novel triterpenoid derivative from Serjania triquetra (Sapindaceae). Biogenetic implications.

Abstract Stigmasterol, oleanolic acid, morolic acid, hederagenin, and 11α-hydroperoxy-hederagenin were isolated and characterized as the sapogenins present in the aerial parts of the medicinal plant Serjania triquetra (Sapindaceae). The structure of the novel triterpenoid derivative, 11α-hydroperoxy-diacetyl hederagenin, considered as a key biogenetic and chemical intermediate, was confirmed by relay synthesis from diacetyl hederagenin, via bromo-lactonization, dehydrobromination, and oxidation with H 2 O 2 . Biogenetic relationships are briefly described.

Di- and triterpenoid acids from Lepechinia caulescens☆

Abstract Above ground parts of Lepechinia caulescens afforded the new diterpene 8α(9α),13α(14α)-diepoxy-abietan-18-oic acid. Additional diterpenoid and triterpenoid acids were also characterized from another population of the same species.

Sesquiterpene lactones from Mikania micrantha and Mikania cordifolia and their cytotoxic and anti-inflammatory evaluation.

The guaianolide 8-epi-mikanokryptin (1) and the melampolide 11Hβ-11,13-dihydromicrantholide (2) along with known sesquiterpene lactones (3-13) and other constituents were isolated from the aerial parts of different populations of Mikania micrantha and Mikania cordifolia collected in several states of Mexico. The relative and absolute configurations of 1 were determined by X-ray diffraction and CD analysis, respectively. Considering the (1)H and (13)C NMR chemical shift similarities and the H-H coupling constant values, a [(1)D(14), (15)D5] conformation was established for micrantholides (2, 8-13). We tested nearly all the sesquiterpene lactones for antiproliferative activity in human cancer cell lines, and they exhibited moderate activity. Additionally, in a mouse ear model of edema induced by TPA, the anti-inflammatory activities were marginal.

Anti-inflammatory and toxicological evaluation of Moussonia deppeana (Schldl. & Cham) Hanst and Verbascoside as a main active metabolite.

ETHNOPHARMACOLOGICAL RELEVANCE Moussonia deppeana, known as Tlachichinole, is a Mexican medicinal plant used for treatment of inflammatory diseases, influenza, diarrhea, gastrointestinal disorders and arthritis. AIM OF THE STUDY In this paper the antioxidant and anti-inflammatory activities as well as the acute and sub-acute toxicological effects were evaluated for the ethanolic extract from aerial parts of M. deppeana, also its phytochemical analysis is described. MATERIALS AND METHODS Phytochemical analysis and compound isolation were performed with thin layer chromatography. The chemical identification of the main compound was performed by (1)H NMR (COSY, NOESY, HSQC and HMBC) spectra. In vitro antioxidant capacity and total phenolic content for the ethanolic extract and its primary fractions was determined by DPPH and Folin-Ciocalteu reagent. Acute and subacute toxicity tests were evaluated on Balb/C mice. Finally acute anti-inflammatory evaluation was tested for a local (TPA) and systemic (carrageenan) murine model. RESULTS The main compound isolated from the ethanolic extract of M. deppeana was Verbascoside, which was isolated from F3 and was identified by (1)H NMR and COSY data. Furthermore oleanolic and ursolic acids were isolated from primary fractions F1 and F2. Ethanolic extract showed IC50 = 6.71mg/mL for DPPH test and 664.12µg QE/mL for the total phenolic content. The LD50 value was >2g/kg by i.g. route in male and female mice. Sub-acute administration (28 days) of the ethanolic extract (1g/kg) did not cause lethality or alter any hematological and biochemical parameters, in addition, histological analysis of the major organs exhibited no structural changes. Anti-inflammatory activity of the ethanolic extract showed an ED50 = 1.5mg/ear and 450mg/kg for TPA and carrageenan test, respectively. Primary fractions generated moderate local and systemic anti-inflammatory activity. CONCLUSION The ethanolic extract from the aerial parts of M. deppeana did not cause any lethality or adverse effect in either of the acute and sub-acute toxicity tests. This exhibited an important local and systemic anti-inflammatory activity and also moderate antioxidant capacity. Moreover, the primary fraction F2 was more active for the TPA model while the primary fraction F3 was most active in the carrageenan model in vivo. The main compound isolated from F3 was verbascoside; on the other hand also ursolic and oleanolic acids were isolated from F1 and F2.

The solid-state and solution-state reassigned structures of tagitinin A, a 3,10-epoxy-germacrolide from Tithonia diversifolia, and the interconversion of 3,10-epoxy-germacrolide conformational families via a ring-atom flip mechanism

Tagitinina A(2), uma 3,10-epoxi-germacrolida-6,7-trans-lactona conhecida e isolada de Tithonia diversifolia foi estudada atraves de difracao de raios-X de monocristal. Verificou-se que a mesma apresenta a configuracao relativa 1b,4a,6a,7b,8b que difere da orientacao 1a em C(1) proposta originalmente na literatura e que foi determinada pelo metodo de Horeau. Analise do espectro de 1H-RMN de 2 em solucao de d6-acetona mostra que a molecula mantem a conformacao twist-chair-boat (TCB) observada cristalograficamente para o anel de 9 membros. As conformacoes twist-chair-boat/skew-chair-boat do tipo 3 para aneis de 9 membros saturados e insaturados dentro das 3,10-epoxi-germacrolidas podem ser convertidas a conformacao skew-chair-chair (SCC) atraves de mecanismo de inversao de C(9) do anel. Como resultado dessa mudanca conformacional, a orientacao de C(1) e de C(8) da unidade oxicarbonila sao transformados de diequatorial para diaxial. A estereoquimica relatada para lactonas do tipo 3,10-epoxi-germacrolida e resultados de modelagem utilizando-se DFT B3LYP/6-31g(d) indicam que os atomos C(1) tetraedricos estabilizam conformacoes TCB/SCB do tipo 3 enquanto que aqueles com geometria trigonal estabilizam a conformacao SCC.