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Andrés H. Thomas - One of the best experts on this subject based on the ideXlab platform.
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Photophysical and Photochemical Properties of 3-methylpterin as a New and More Stable Pterin-type Photosensitizer
Photochemistry and Photobiology, 2018Co-Authors: Sandra Estébanez, Teodoro S. Kaufman, Enrique L. Larghi, Carolina Lorente, Andrés H. Thomas, Mariana P. SerranoAbstract:Pterin derivatives are heterocyclic compounds which are present in different biological systems. Neutral aqueous solutions of Pterins present acid-base and keto-enol equilibria. These compounds, under UV-A radiation fluoresce, undergo photooxidation, generate reactive oxygen species and photoinduce the oxidation of biological substrates. As photosensitizers, they may act through different mechanisms, mainly through an electron transfer-initiated process (type-I mechanism), but they also produce singlet molecular oxygen (1 O2 ) upon irradiation (type-II mechanism). In general, upon UV-A excitation two triplet states, corresponding to the lactim and lactam tautomers, are formed, but only the last one is the responsible for the photosensitized reactions of biomolecules. We present a study of the photochemical properties of 3-methylpterin (3-Mep) which, in contrast to most pterin derivatives, exists only in the lactam form. Also an improvement in the synthesis of 3-Mep is reported. The spectroscopic properties 3-Mep in aqueous solution were similar to those of the unsubstituted pterin derivative (Ptr) in its acid form, such as absorption, fluorescent and phosphorescent emission spectra. Experiments using 2'-deoxyguanosine 5'-monophosphate (dGMP) as oxidizable target demonstrated that methylation at C-3 position of the pterin moiety does not affect significantly the efficiency of photosensitization, but results in a more photostable sensitizer.
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Kinetic Control in the Regioselective Alkylation of Pterin Sensitizers: A Synthetic, Photochemical, and Theoretical Study
Photochemistry and Photobiology, 2018Co-Authors: Niluksha Walalawela, Andrés H. Thomas, Mariana Vignoni, María Noel Urrutia, Sarah J. Belh, Edyta M. Greer, Alexander GreerAbstract:Alkylation patterns and excited-state properties of Pterins were examined both experimentally and theoretically. 2D NMR spectroscopy was used to characterize the pterin derivatives, revealing undoubtedly that the decyl chains were coupled to either the O4 or N3 sites on the pterin. At a temperature of 70°C, the pterin alkylation regioselectively favored the O4 over the N3. The O4 was also favored when using solvents, in which the reactants had increased solubility, namely N,N-dimethylformamide and N,N-dimethylacetamide, rather than solvents in which the reactants had very low solubility (tetrahydrofuran and dichloromethane). Density functional theory (DFT) computed enthalpies correlate to regioselectivity being kinetically driven because the less stable O-isomer forms in higher yield than the more stable N-isomer. Once formed these compounds did not interconvert thermally or undergo a unimolecular "walk" rearrangement. Mechanistic rationale for the factors underlying the regioselective alkylation of Pterins is suggested, where kinetic rather than thermodynamic factors are key in the higher yield of the O-isomer. Computations also predicted greater solubility and reduced triplet state energetics thereby improving the properties of the alkylated Pterins as 1 O2 sensitizers. Insight on thermal and photostability of the alkylated Pterins is also provided.
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Effect of pterin impurities on the fluorescence and photochemistry of commercial folic acid.
Journal of Photochemistry and Photobiology B-biology, 2018Co-Authors: M. Laura Dántola, M. Noel Urrutia, Andrés H. ThomasAbstract:Abstract Folic acid, or pteroyl‑ l ‑glutamic acid (PteGlu) is a conjugated pterin derivative that is used in dietary supplementation as a source of folates, a group of compounds essential for a variety of physiological functions in humans. Photochemistry of PteGlu is important because folates are not synthesized by mammals, undergo photodegradation and their deficiency is related to many diseases. We have demonstrated that usual commercial PteGlu is unpurified with the unconjugated oxidized Pterins 6‑formylpterin (Fop) and 6‑carboxypterin (Cap). These compounds are in such low amounts that a normal chromatographic control would not detect any pterinic contamination. However, the fluorescence of PteGlu solutions is due to the emission of Fop and Cap and the contribution of the PteGlu emission, much lower, is negligible. This is because the fluorescence quantum yield (ΦF) of PteGlu is extremely weak compared to the ΦF of Fop and Cap. Likewise, the PteGlu photodegradation upon UV-A radiation is an oxidation photosensitized by oxidized unconjugated Pterins present in the solution, and not a process initiated by the direct absorption of photons by PteGlu. In brief, the fluorescence and photochemical properties of PteGlu solutions, prepared using commercially available solids, are due to their unconjugated Pterins impurities and not to PteGlu itself. This fact calls into question many reported studies on fluorescence and photooxidation of this compound.
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Photosensitization of peptides and proteins by pterin derivatives
Pteridines, 2017Co-Authors: M. Laura Dántola, Carolina Lorente, Esther Oliveros, Lara O. Reid, Carolina Castaño, Andrés H. ThomasAbstract:AbstractProteins are one of the preferential targets of the photosensitized damaging effects of ultraviolet (UV) radiation on biological system. Pterins belong to a family of heterocyclic compounds, which are widespread in living systems and participate in relevant biological functions. In pathological conditions, such as vitiligo, oxidized Pterins accumulate in the white skin patches of patients suffering this depigmentation disorder. It is known that Pterins are able to photosensitize damage in nucleotides and DNA by type I (electron transfer) and type II (singlet oxygen) mechanisms. Recently, it has been demonstrated that proteins and its components may also be damaged when solutions containing both proteins and pterin are exposed to UV-A radiation. Therefore, given the biological and medical relevance of the photosensitizing properties of these molecules, we present in this article an overview of the capability of different pterin derivatives to photoinduce damage in proteins present in the skin, focusing our attention on the chemical modifications of tyrosine and tryptophan residues.
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Lipophilic Decyl Chain–Pterin Conjugates with Sensitizer Properties
Molecular Pharmaceutics, 2017Co-Authors: Mariana Vignoni, Niluksha Walalawela, Sergio M. Bonesi, Alexander Greer, Andrés H. ThomasAbstract:A new series of decyl chain [−(CH2)9CH3] pterin conjugates have been investigated by photochemical and photophysical methods, and with theoretical solubility calculations. To synthesize the Pterins, a nucleophilic substitution (SN2) reaction was used for the regioselective coupling of the alkyl chain to the O site over the N3 site. However, the O-alkylated pterin converts to N3-alkylated pterin under basic conditions, pointing to a kinetic product in the former and a thermodynamic product in the latter. Two additional adducts were also obtained from an N-amine condensation of DMF solvent molecule as byproducts. In comparison to the natural product pterin, the alkyl chain Pterins possess reduced fluorescence quantum yields (ΦF) and increased singlet oxygen quantum yields (ΦΔ). It is shown that the DMF-condensed Pterins were more photostable compared to the N3- and O-alkylated Pterins bearing a free amine group. The alkyl chain Pterins efficiently intercalate in large unilamellar vesicles, which is a good i...
Roger Klein - One of the best experts on this subject based on the ideXlab platform.
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identification stereoconfiguration chromatographic and fluorescence properties of natural Pterins
Advances in Experimental Medicine and Biology, 1993Co-Authors: Roger KleinAbstract:Several years ago, we reported the identification of dictyopterin as 6-[D-threo]-1’, 2’-dihydroxy propyl-pterin1. Such a result had been obtained after numerous and tedious purification steps. In order to facilitate the determination of the stereoconfiguration of natural Pterins, which are found in very small amounts in living organisms, we aimed to find a sensitive method. This was achieved in using chiral HPLC. The separation of D-and L-enantiomers of 6-(polyhydroxypropyl)-Pterins was obtained by ligand exchange chromatography in using a reversed-phase column with a mobile phase containing D-phenylalanine as the chiral modifier and Cu(II) as the metal ion. This enantiomeric separation allowed the stereoconfiguration of some natural Pterins to be deterriiined in the picomole range, by comparison of their chromatographic and fluorescence properties with those of reference enantiomeric Pterins2. The present paper briefly reports an aspect of the method dealing with the fluorescence quantum yields of Pterins and describes one application which answers the following questions : what is the stereoconfiguration of urinary monapterin ? Are there any differences in human urine from cancer and non-cancer patients?
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determination of the stereoconfiguration of natural Pterins by chiral high performance liquid chromatography
Analytical Biochemistry, 1992Co-Authors: Roger KleinAbstract:Abstract The separation of d - and l -enantiomers of 6-(polyhydroxypropyl)Pterins was obtained by ligand-exchange chromatography using a reversed-phase column at 12°C with a mobile phase containing d -phenylalanine as the chiral modifier and Cu(II) as the metal ion. This allowed the determination of the stereoconfiguration of natural Pterins from very small amounts of biological sample containing Pterins in the picomole range (nanogram range). Fluorescence detection was used both to increase the sensitivity and to confirm the identification by on-line fluorescence spectroscopy and comparison with reference compounds. The stereoconfiguration of optically active Pterins present in a bacterium ( Escherichia coli ), in a ciliate protozoan ( Tetrahymena pyriformis ), in an amoeba ( Dictyostelium discoideum ), and in mammals (human urine) was obtained and compared to earlier determinations. Incidental findings resulting from the application of this method were that human urinary monapterin and the major pterin of T. pyriformis were identified as a d -monapterin, which, until now, was not known as a natural pterin.
Carolina Lorente - One of the best experts on this subject based on the ideXlab platform.
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Photophysical and Photochemical Properties of 3-methylpterin as a New and More Stable Pterin-type Photosensitizer
Photochemistry and Photobiology, 2018Co-Authors: Sandra Estébanez, Teodoro S. Kaufman, Enrique L. Larghi, Carolina Lorente, Andrés H. Thomas, Mariana P. SerranoAbstract:Pterin derivatives are heterocyclic compounds which are present in different biological systems. Neutral aqueous solutions of Pterins present acid-base and keto-enol equilibria. These compounds, under UV-A radiation fluoresce, undergo photooxidation, generate reactive oxygen species and photoinduce the oxidation of biological substrates. As photosensitizers, they may act through different mechanisms, mainly through an electron transfer-initiated process (type-I mechanism), but they also produce singlet molecular oxygen (1 O2 ) upon irradiation (type-II mechanism). In general, upon UV-A excitation two triplet states, corresponding to the lactim and lactam tautomers, are formed, but only the last one is the responsible for the photosensitized reactions of biomolecules. We present a study of the photochemical properties of 3-methylpterin (3-Mep) which, in contrast to most pterin derivatives, exists only in the lactam form. Also an improvement in the synthesis of 3-Mep is reported. The spectroscopic properties 3-Mep in aqueous solution were similar to those of the unsubstituted pterin derivative (Ptr) in its acid form, such as absorption, fluorescent and phosphorescent emission spectra. Experiments using 2'-deoxyguanosine 5'-monophosphate (dGMP) as oxidizable target demonstrated that methylation at C-3 position of the pterin moiety does not affect significantly the efficiency of photosensitization, but results in a more photostable sensitizer.
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Photosensitization of peptides and proteins by pterin derivatives
Pteridines, 2017Co-Authors: M. Laura Dántola, Carolina Lorente, Esther Oliveros, Lara O. Reid, Carolina Castaño, Andrés H. ThomasAbstract:AbstractProteins are one of the preferential targets of the photosensitized damaging effects of ultraviolet (UV) radiation on biological system. Pterins belong to a family of heterocyclic compounds, which are widespread in living systems and participate in relevant biological functions. In pathological conditions, such as vitiligo, oxidized Pterins accumulate in the white skin patches of patients suffering this depigmentation disorder. It is known that Pterins are able to photosensitize damage in nucleotides and DNA by type I (electron transfer) and type II (singlet oxygen) mechanisms. Recently, it has been demonstrated that proteins and its components may also be damaged when solutions containing both proteins and pterin are exposed to UV-A radiation. Therefore, given the biological and medical relevance of the photosensitizing properties of these molecules, we present in this article an overview of the capability of different pterin derivatives to photoinduce damage in proteins present in the skin, focusing our attention on the chemical modifications of tyrosine and tryptophan residues.
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Thymidine radical formation via one-electron transfer oxidation photoinduced by pterin: Mechanism and products characterization.
Free Radical Biology and Medicine, 2016Co-Authors: Mariana P. Serrano, Carolina Lorente, Esther Oliveros, Mariana Vignoni, Patricia Vicendo, Andrés H. ThomasAbstract:Abstract UV-A radiation (320–400 nm), recognized as a class I carcinogen, induces damage to the DNA molecule and its components through different mechanisms. Pterin derivatives are involved in various biological functions, including enzymatic processes, and it has been demonstrated that oxidized Pterins may act as photosensitizers. In particular, they accumulate in the skin of patients suffering from vitiligo, a chronic depigmentation disorder. We have investigated the ability of pterin (Ptr), the parent compound of oxidized Pterins, to photosensitize the degradation of the pyrimidine nucleotide thymidine 5′-monophosphate (dTMP) in aqueous solutions under UV-A irradiation. Although thymine is less reactive than purine nucleobases, our results showed that Ptr is able to photoinduce the degradation of dTMP and that the process is initiated by an electron transfer from the nucleotide to the triplet excited state of Ptr. In the presence of molecular oxygen, the photochemical process leads to the oxidation of dTMP, whereas Ptr is not consumed. In the absence of oxygen, both compounds are consumed to yield a product in which the pterin moiety is covalently linked to the thymine. This compound retains some of the spectroscopic properties of Ptr, such as absorbance in the UV-A region and fluorescence properties.
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Histidine oxidation photosensitized by pterin: pH dependent mechanism.
Journal of Photochemistry and Photobiology B-biology, 2015Co-Authors: Carolina Castaño, Andrés H. Thomas, Esther Oliveros, Carolina LorenteAbstract:Abstract Aromatic Pterins accumulate in the skin of patients suffering from vitiligo, a chronic depigmentation disorder, due to the oxidation of tetrahydrobiopterin, the biologically active form of Pterins. In this work, we have investigated the ability of pterin, the parent compound of aromatic Pterins, to photosensitize the oxidation of histidine in aqueous solutions under UV-A irradiation. Histidine is an α-amino acid with an imidazole functional group, and is frequently present at the active sites of enzymes. The results highlight the role of the pH in controlling the competition between energy and electron transfer mechanisms. It has been previously demonstrated that Pterins participate as sensitizers in photosensitized oxidations, both by type I (electron-transfer) and type II mechanisms (singlet oxygen (1O2)). By combining different analytical techniques, we could establish that a type I photooxidation was the prevailing mechanism at acidic pH, although a type II mechanism is also present, but it is more important in alkaline solutions.
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unraveling the degradation mechanism of purine nucleotides photosensitized by Pterins the role of charge transfer steps
ChemPhysChem, 2015Co-Authors: Mariana P. Serrano, Carolina Lorente, Claudio D. Borsarelli, Andrés H. ThomasAbstract:: Photosensitized reactions contribute to the development of skin cancer and are used in many applications. Photosensitizers can act through different mechanisms. It is currently accepted that if the photosensitizer generates singlet molecular oxygen ((1) O2 ) upon irradiation, the target molecule can undergo oxidation by this reactive oxygen species and the reaction needs dissolved O2 to proceed, therefore the reaction is classified as (1) O2 -mediated oxidation (type II mechanism). However, this assumption is not always correct, and as an example, a study on the degradation of 2'-deoxyguanosine 5'-monophosphate photosensitized by pterin is presented. A general mechanism is proposed to explain how the degradation of biological targets, such as nucleotides, photosensitized by Pterins, naturally occurring (1) O2 photosensitizers, takes place through an electron-transfer-initiated process (type I mechanism), whereas the contribution of the (1) O2 -mediated oxidation is almost negligible.
Steven P Gieseg - One of the best experts on this subject based on the ideXlab platform.
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Pterins as diagnostic markers of exercise induced stress a systematic review
Journal of Science and Medicine in Sport, 2020Co-Authors: Angus Lindsay, Steven P GiesegAbstract:Abstract Objectives To evaluate Pterins as diagnostic biomarkers of exercise-induced stress. Design Systematic review of the literature. Methods MEDLINE, Scopus and Web of Science were searched in March 2019 for relevant literature. We only considered in vivo studies of healthy humans that reported measurement of a pterin(s) in response to exercise or sport with no underlying prior disease or complication. Relevant articles were independently reviewed and resolved by consensus. Results We included 29 studies with 644 participants. We classified articles by running/hiking, cycling, rugby, mixed martial arts (MMA) or other. Eighty-six percent of studies measured a significant increase in a pterin in response to exercise. Changes in pterin concentrations were within 24 h of the exercise-stimulus in 79% of studies and 17% measured a change from baseline greater than 48 h post-exercise (49% did not measure or report beyond 48 h). Neopterin or total neopterin (neopterin + 7,8-dihydroneopterin) were the primary pterin measured (28 studies) and they were equally sensitive to exercise regardless of whether the stimulus was running, cycling, rugby, MMA or other. Conclusions Neopterin and total neopterin increase in response to exercise-induced stress. Pterins may have limited capacity for monitoring long-term stress beyond 48 h but further research is required.
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Pterins as diagnostic markers of mechanical and impact induced trauma a systematic review
Journal of Clinical Medicine, 2019Co-Authors: Angus Lindsay, Gregory Baxterparker, Steven P GiesegAbstract:We performed a systematic review of the literature to evaluate Pterins as biomarkers of mechanical and impact-induced trauma. MEDLINE and Scopus were searched in March 2019. We included in vivo human studies that measured a pterin in response to mechanical or impact-induced trauma with no underlying prior disease or complication. We included 40 studies with a total of 3829 subjects. Seventy-seven percent of studies measured a significant increase in a pterin, primarily neopterin or total neopterin (neopterin + 7,8-dihydroneopterin). Fifty-one percent of studies measured an increase within 24 h of trauma, while 46% measured increases beyond 48 h. Pterins also showed promise as predictors of post-trauma complications such as sepsis, multi-organ failure and mortality. Exercise-induced trauma and traumatic brain injury caused an immediate increase in neopterin or total neopterin, while patients of multiple trauma had elevated pterin levels that remained above baseline for several days. Pterin concentration changes in response to surgery were variable with patients undergoing cardiac surgery having immediate and sustained pterin increases, while gastrectomy, liver resection or hysterectomy showed no change. This review provides systematic evidence that Pterins, in particular neopterin and total neopterin, increase in response to multiple forms of mechanical or impact-induced trauma.
Esther Oliveros - One of the best experts on this subject based on the ideXlab platform.
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Photosensitization of peptides and proteins by pterin derivatives
Pteridines, 2017Co-Authors: M. Laura Dántola, Carolina Lorente, Esther Oliveros, Lara O. Reid, Carolina Castaño, Andrés H. ThomasAbstract:AbstractProteins are one of the preferential targets of the photosensitized damaging effects of ultraviolet (UV) radiation on biological system. Pterins belong to a family of heterocyclic compounds, which are widespread in living systems and participate in relevant biological functions. In pathological conditions, such as vitiligo, oxidized Pterins accumulate in the white skin patches of patients suffering this depigmentation disorder. It is known that Pterins are able to photosensitize damage in nucleotides and DNA by type I (electron transfer) and type II (singlet oxygen) mechanisms. Recently, it has been demonstrated that proteins and its components may also be damaged when solutions containing both proteins and pterin are exposed to UV-A radiation. Therefore, given the biological and medical relevance of the photosensitizing properties of these molecules, we present in this article an overview of the capability of different pterin derivatives to photoinduce damage in proteins present in the skin, focusing our attention on the chemical modifications of tyrosine and tryptophan residues.
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Degradation of tyrosine and tryptophan residues of peptides by type I photosensitized oxidation.
Journal of Photochemistry and Photobiology B-biology, 2016Co-Authors: Carolina Castaño, Esther Oliveros, Mariana Vignoni, Patricia Vicendo, Andrés H. ThomasAbstract:Abstract Pterin derivatives are involved in various biological functions, including enzymatic processes that take place in human skin. Unconjugated oxidized Pterins are efficient photosensitizers under UV-A irradiation and accumulate in the skin of patients suffering from vitiligo, a chronic depigmentation disorder. These compounds are able to photoinduce the oxidation of the peptide α-melanocyte-stimulating hormone (α-MSH), which stimulates the production and release of melanin by melanocytes in skin and hair. In the present work we have used two peptides in which the amino acid sequence of α-MSH was mutated to specifically investigate the reactivity of tryptophan (Trp) and tyrosine residues (Tyr). The parent compound of oxidized Pterins (Ptr) was used as a model photosensitizer in aqueous solution at pH 5.5 and was exposed to UV-A radiation, a wavelength range where the peptides do not absorb. Trp residue yields N-formylkynurenine and hydroxytryptophan as oxidized products, whereas the Tyr undergoes dimerization and incorporation of oxygen atoms. In both cases, the first step of the mechanism involves an electron transfer from the amino acid to the photosensitizer triplet excited state, Ptr is not consumed and hydrogen peroxide (H2O2) is released. The role of singlet oxygen produced by energy transfer from 3Ptr⁎ to dissolved O2 was negligible or minor. Other amino acid residues, such as histidine, might be also affected.
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Thymidine radical formation via one-electron transfer oxidation photoinduced by pterin: Mechanism and products characterization.
Free Radical Biology and Medicine, 2016Co-Authors: Mariana P. Serrano, Carolina Lorente, Esther Oliveros, Mariana Vignoni, Patricia Vicendo, Andrés H. ThomasAbstract:Abstract UV-A radiation (320–400 nm), recognized as a class I carcinogen, induces damage to the DNA molecule and its components through different mechanisms. Pterin derivatives are involved in various biological functions, including enzymatic processes, and it has been demonstrated that oxidized Pterins may act as photosensitizers. In particular, they accumulate in the skin of patients suffering from vitiligo, a chronic depigmentation disorder. We have investigated the ability of pterin (Ptr), the parent compound of oxidized Pterins, to photosensitize the degradation of the pyrimidine nucleotide thymidine 5′-monophosphate (dTMP) in aqueous solutions under UV-A irradiation. Although thymine is less reactive than purine nucleobases, our results showed that Ptr is able to photoinduce the degradation of dTMP and that the process is initiated by an electron transfer from the nucleotide to the triplet excited state of Ptr. In the presence of molecular oxygen, the photochemical process leads to the oxidation of dTMP, whereas Ptr is not consumed. In the absence of oxygen, both compounds are consumed to yield a product in which the pterin moiety is covalently linked to the thymine. This compound retains some of the spectroscopic properties of Ptr, such as absorbance in the UV-A region and fluorescence properties.
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Histidine oxidation photosensitized by pterin: pH dependent mechanism.
Journal of Photochemistry and Photobiology B-biology, 2015Co-Authors: Carolina Castaño, Andrés H. Thomas, Esther Oliveros, Carolina LorenteAbstract:Abstract Aromatic Pterins accumulate in the skin of patients suffering from vitiligo, a chronic depigmentation disorder, due to the oxidation of tetrahydrobiopterin, the biologically active form of Pterins. In this work, we have investigated the ability of pterin, the parent compound of aromatic Pterins, to photosensitize the oxidation of histidine in aqueous solutions under UV-A irradiation. Histidine is an α-amino acid with an imidazole functional group, and is frequently present at the active sites of enzymes. The results highlight the role of the pH in controlling the competition between energy and electron transfer mechanisms. It has been previously demonstrated that Pterins participate as sensitizers in photosensitized oxidations, both by type I (electron-transfer) and type II mechanisms (singlet oxygen (1O2)). By combining different analytical techniques, we could establish that a type I photooxidation was the prevailing mechanism at acidic pH, although a type II mechanism is also present, but it is more important in alkaline solutions.
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Oxidation of Tyrosine Photoinduced by Pterin in Aqueous Solution
Photochemistry and Photobiology, 2013Co-Authors: Carolina Castaño, M. Laura Dántola, Esther Oliveros, Andrés H. Thomas, Carolina LorenteAbstract:Pterins, heterocyclic compounds widespread in biological systems, accumulate in the skin of patients suffering from vitiligo, a chronic depigmentation disorder. Pterins have been previously identified as good photosensitizers under UV-A irradiation. In this work, we have investigated the ability of pterin (Ptr), the parent compound of oxidized Pterins, to photosensitize the oxidation of tyrosine (Tyr) in aqueous solutions. Tyr is an important target in the study of the photodynamic effects of UV-A radiation because it is oxidized by singlet oxygen (1O2) and plays a key role in polymerization and cross-linking of proteins. Steady UV-A irradiation of solutions containing Ptr and Tyr led to the consumption of Tyr and dissolved O2, whereas the Ptr concentration remained unchanged. Concomitantly, hydrogen peroxide (H2O2) was produced. By combining different analytical techniques, we could establish that the mechanism of the photosensitized process involves an electron transfer from Tyr to the triplet excited state of Ptr. Mass spectrometry, chromatography and fluorescence were used to analyze the photoproducts. In particular, oxygenated and dimeric compounds were identified.