Seven quinic acid gallates from quercus stenophylla

A chemical investigation of the bark of Quercus stenophylla has led to the isolation and characterization of all of the possible structural isomers of quinic acid gallates; 3-O-, 4-O-, 5-O-, 3,4-di-O-, 3,5-di-O-, 4,5-di-O- and 3,4,5-tri-O-galloylquinic acids. Evidence for the structures of these compounds was obtained from analysis of the ¹H and ¹³C NMR spectra, and hydrolytic studies.     

Studies on quinic acid biosynthesis in Quercus pedunculata Ehrh. seedlings

The time course of ¹⁴C incorporation into shikimic (SA) andquinic acids (QA) was examined in Quercus pedunculata seedlingsof different age fed with ¹⁴C glucose-6-phosphate (G6P) or ¹⁴Cdehydroquinic acid (DHQ). QA was actively synthesized from G6Pand exhibited the highest radioactivity among the organic acids.In contrast, DHQ, a good precursor of shikimate, was poor forquinate synthesis. In both cases, QA and SA presented parallelchanges in specific radioactivities with time. The experimental results suggest that in oak leaves QA is formedby a route that is independent of the shikimate pathway andthat this compound undergoes an important turnover. Moreover,depending on the physiological state of the plants, there aredifferences in the relative biosynthetic rates of the two acids. (Received April 23, 1980; )     

Polycarbonates from the polyhydroxy natural product quinic acid

Strategies for the preparation of polycarbonates, derived from natural polyhydroxy monomeric repeat units, were developed for biosourced polycarbonates based on quinic acid. The design and synthesis of regioselectively tert-butyldimethylsilyloxy (TBS)-protected 1,4- and 1,5-diol monomers of quinic acid were followed by optimization of their copolymerizations with phosgene, generated in situ from trichloromethyl chloroformate, to yield protected poly(1,4-quinic acid carbonate) and poly(1,5-quinic acid carbonate). The molecular weights reached ca. 7.6 kDa, corresponding to degrees of polymerization of ca. 24, with polydispersities ranging from 2.0 to 3.5, as measured by SEC using tetrahydrofuran as the eluent and with polystyrene calibration standards. Partially because of the presence of the bicyclic backbone, each regioisomeric poly(quinic acid carbonate) exhibited relatively high glass-transition temperatures, 209 °C for poly(1,4-quinic acid carbonate) and 229 °C for poly(1,5-quinic acid carbonate). Removal of the TBS-protecting groups was studied under mild conditions to achieve control over potential competing reactions involving polymer degradation, which could include cleavage of lactones within the repeat units, carbonate linkages, or both between the repeat units. Full deprotection was not achieved without some degree of polymer degradation. The regiochemistry of the monomer showed significant impact on the reactivity during deprotection and also on the thermal properties, with the 1,5-regioisomeric polymer having lower reactivity and giving higher T(g) values, in comparison with the 1,4-regioisomer. Each regioisomer underwent a 10-20 °C increase in T(g) upon partial removal of the TBS-protecting groups. As the extent of deprotection increased, the solubility decreased. Ultimately, at long deprotection reaction times, the solubility increased and the T(g) decreased because of significant degradation of the polymers.     

Thermodynamics of interaction of caffeic acid and quinic acid with multisubunit proteins

Helianthinin is a multisubunit protein from Sunflower seeds. Caffeic acid (CA) and quinic acid (QA) are intrinsic ligands present in sunflower seeds. The mechanism of interaction of these ligands with multisubunit proteins is limited. The present study enables one to understand the mechanism of the interaction of these ligands with the protein helianthinin. From this study, it is shown that CA has two classes of binding sites on helianthinin. The high-affinity class of sites total six from 60+/-10 for both high-affinity and low-affinity sites. Tryptophan, tyrosine and lysine residues of the protein are mainly involved in the interaction with CA. The temperature dependence of the binding in the range 10-45 degrees C can be clearly described by an enthalpy-entropy compensation effect at the low-affinity class of sites, while it is described by positive DeltaC(p)(o) at the high-affinity class of sites. This positive DeltaC(p)(o) has a contribution to the protein stability. The binding strength of CA also has a positive cooperativity at higher protein concentration. QA has two classes of binding sites on the protein based on the strength of the interaction. The interaction of QA with the protein is predominantly described by positive DeltaC(p)(o) for both classes of affinity. This suggests predominance of ionic/hydrogen bonding in the interaction process. Differential scanning calorimetric measurements reveal that the binding of both CA and QA induces destabilisation of the subunit-subunit interaction. Human methaemoglobin (mHb) has two binding sites on the molecule for CA. Both CA and QA decrease the stability of mHb, as indicated by decreased T(m). This destabilisation is also accompanied by dissociation to the monomers with concomitant conformational changes.     

Two new quinic acid derivatives from the fruits of Chaenomeles speciosa

Two new quinic acid derivatives (1, 2), together containing eighteen (3–20) known compounds, were isolated from the fruits of Chaenomeles speciosa. Spectroscopic methods and previous data retrieved from the literature were used to determine the chemical structures of the compounds. Among the compounds, quinic acid derivatives (3, 4, 6, 7), phenolic acid compounds (8, 10, 11) and catechin derivatives (18, 19, 20) were isolated for the first time from the family Chaenomeles. The chemotaxonomic significance of the compounds was also discussed.     

Distribution of quinic acid derivatives and other phenolic compounds in Brazilian propolis

The quinic acid derivatives (including 4-feruoyl quinic and 5-ferruoyl quinic acids characterized for first time in propolis samples) and other phenolic compounds were quantified in thirteen Brazilian propolis samples by HPLC analysis. For chemometrical analysis, the distribution of quinic acid derivatives and other phenolic compounds were considered. The results suggest that the Brazilian propolis with floral origin from Citrus sp. have the highest concentration of the quinic acid derivatives (between 11.0 to 58.4 mg/mg of the dried crude hydroalcoholic extract) and therefore would probably show a more effective hepatoprotective activity.     

Two new quinic acid derivatives and one new lignan glycoside from Erycibe obtusifolia

Three new compounds, 4-{erythro-2-[3-(4-hydroxyl-3-methoxyphenyl)-3-O-β-d-glucopyranosyl-propan-1-ol]}-O-medioresinol (1), (7⿳E,9⿳E,1⿳R*,3⿳S*,5⿳R*,6⿳S*)-5-O-caffeoyl-3-O-dihydrophaseicoylquinic acid (2), and (7⿳E,9⿳E,1⿳R*,3⿳S*,5⿳R*,6⿳S*)-5-O-caffeoyl-4-O-dihydrophaseicoylquinic acid (3), were isolated from Chinese folk herb Erycibe obtusifolia together with six known compounds (4⿿9). Their structures were elucidated on the basis of comparisons of literatures and extensive spectroscopic analysis, including UV, IR, HRMS, and 1D and 2D NMR techniques. Further, the cytotoxicities of these compounds were evaluated against five cell lines (HCT-8, Bel-7402, BGC-823, A549, and A2780), but they were inactive against these tumor cell lines (IC₅₀ > 10 μmol/L).     

Effects of caffeoyl conjugates of isoprenyl-hydroquinone glucoside and quinic acid on leukocyte function

The activity of three prenylhydroquinone glucosides (1-3) and four caffeoylquinic esters (4-7), obtained from Phagnalon rupestre, on elastase release, myeloperoxidase activity and superoxide and leukotriene B(4) production from polymorphonuclear leukocytes was determined. 4,5-Dicaffeoylquinic acid strongly inhibited elastase release with an IC(50) value of 4.8 microM. Methylated caffeoylquinic derivatives were the most potent inhibitors of myeloperoxidase (IC(50) near 60 microM), whereas both methylated and free carboxyl isomers inhibited superoxide production with similar potency (IC(50) between 27 and 42 microM). The monocaffeoyl conjugate of prenylhydroquinone glucoside (3), the most potent inhibitor of leukotriene B(4) production (IC(50) = 33 microM), possesses a mixed hydroquinone-caffeoyl character that could be considered as a potential anti-inflammatory entity.     

Molecular organisation of the quinic acid utilization (QUT) gene cluster in Aspergillus nidulans

Summary The functional integrity of the QUTB gene (encoding quinate dehydrogenase) has been confirmed by transformation of a qutB mutant strain. The DNA sequence of the contiguous genes QUTD (quinate permease), QUTB and QUTG (function unknown) has been determined and analysed, together with that of QUTE (catabolic 3-dehydroquinase). The QUTB sequence shows significant homology with the shikimate dehydrogenase function of the complex AROM locus of Aspergillus nidulans, and with the QA-3 quinate dehydrogenase and QA-1S (repressor) genes of Neurospora crassa. The QUTD gene shows strong homology with the N. crassa QA-Y gene and QUTG with the QA-X gene. QUTD, QUTB, and QUTG, QUTE form two pairs of divergently transcribed genes, and conserved sequence motifs identified in the two common 5 non-coding regions show significant homology with UAS _GAL and UAS _QA sequences of the Saccharomyces cerevisiae and N. crassa Gal and QA systems. In addition, conserved 5 sequences homologous to the mammalian CAAT box are noted and a previously unreported conserved 22 nucleotide motif is presented.     

Genetic regulation of the quinic acid utilization (QUT) gene cluster in Aspergillus nidulans

A large number of quinic acid non-utilizing qut mutants of Aspergillus nidulans deficient in the induction of all three quinic acid specific enzymes have been analysed. One class the qutD mutants, are all recessive and are non-inducible at pH 6.5 due to inferred deficiency in a quinate ion permease. Two regulatory genes have been identified. The QUTA gene encodes an activator protein since most qutA mutants are recessive and non-inducible although a few fully dominant mutants have been found. The QUTR gene encodes a repressor protein since recessive mutations are constitutive for all three enzyme activities. Rare dominant non-inducible mutants which revert readily to yield a high proportion of constitutive strains are inferred to be qutR mutants defective in binding the inducer. The gene cluster has been mapped in the right arm of chromosome VIII in the order: centromere - greater than 50 map units - ornB - 12 map units - qutC (dehydratase)-0.8 map units-qutD (permease), qutB (dehydrogenase), qutE (dehydroquinase), qutA (activator)-4.4 map units - qutR (repressor)-20 map units - galG. This organization differs from that of the qa gene cluster in Neurospora crassa, particularly in the displacement of qutC and qutR.     

Purification and characterization of catabolic dehydroquinase, an enzyme in the inducible quinic acid catabolic pathway of Neurospora crassa.

Catabolic dehydroquinase which functions in the inducible quinic acid catabolic pathway in Neurospora crassa has been purified 8000-fold. The enzyme was purified by two methods. One used heat denaturation of contaminating proteins; the other used antibody affinity chromatography. The preparations obtained by these two methods were identical by all criteria. The purified enzyme is extremely resistant to thermal denaturation as well as denaturation 0y urea and guanidine hydrochloride at 25 degrees. It is irreversibly inactivated, although not efficiently dissociated, by sodium dodecyl sulfate and guanidine hydrochloride at 55 degrees. At pH 3.0, the enzyme is reversibly dissociated into inactive subunits. At high concentrations catabolic dehydroquinase aggregates into an inactive, high molecular weight complex. The native enzyme, which has a very high specific activity, has a molecular weight of approximately 220,000 and is composed of identical subunits of 8,000 to 12,000 molecular weight each. The native enzyme and the subunit are both asymmetric.