Sodium paeoniflorin sulfonate, a process derived artefact from paeoniflorin

Metabolomics analysis of peony root using NMR spectroscopy and impact of the preprocessing method for NMR data in multivariate analysis

Peony root is an important herbal drug used as an antispasmodic analgesic. To evaluate peony roots with different botanical origins, producing areas, and post-harvest processing, 1H NMR-based metabolomics analysis was employed. Five types of monoterpenoids, including albiflorin (4), paeoniflorin (6), and sulfonated paeoniflorin (25), and six other compounds, including 1,2,3,4,6-penta-O-galloyl-β-D-glucose (18), benzoic acid (21), gallic acid (22), and sucrose (26) were detected in the extracts of peony root samples. Among them, compounds 4, 6, 18, and total monoterpenoids including 21 were quantified by quantitative 1H NMR (qHNMR). Compound 25 was detected in 1H NMR spectra of sulfur-fumigated white peony root (WPR) extracts indicating that 1H NMR was a fast and effective method for identifying sulfur-fumigated WPR. The content of 26, the main factor affecting extract yield, increased significantly in peony root after low-temperature storage for one month, whereas that in WPR did not increase due to the boiling treatment after harvesting. We investigated the impact of preprocessing methods to such analysis for NMR data from commercial samples, resulting that the data matrix transformed from qHNMR spectra and normalized to internal standard were optimum for multivariate analysis. The multivariate analysis demonstrated that among commercial samples derived from P. lactiflora, peony root samples in Japanese market (PR) had high contents of 18 and 22, and red peony root (RPR) samples had high content of monoterpenoids represented by 6; and among RPR samples, those derived from P. veitchii showed higher contents of 18 and 22 than those from P. lactiflora. The 1H NMR-based metabolomics method coupled with qHNMR was useful for evaluation of peony root and would be applicable for other crude drugs.

An integrated strategy for evaluation of sulfur-fumigated edible herb Astragali Radix based on UPLC-MS/MS platforms and pharmacological analysis

Astragali Radix is an edible herb that has been employed in Traditional Chinese medicine (TCM) and has recently been recognized by various countries; however, it is also one of the most extensively sulfur-fumigated TCM components. This study designed a UPLC-QTOF-MS/MS-guided isolation approach to generate sulfur-containing derivatives, and a novel sulfur-containing marker, namely, astragaloside sulfate, was characterized based on 1D and 2D NMR, which were derived from the main component of Astragali Radix, namely, astragaloside. Pharmacological experiments also showed that the activity of astragaloside decreased after it was converted into sulfate. Moreover, a rapid assay for the determination of astragaloside sulfate content by UPLC-QTRAP-MS/MS was established to evaluate samples that were non-fumigated and sulfur-fumigated at different levels. The method was applied to determine the content of JGS in the different batches of commercial samples. This research reveals that the practical procedure-based typical sulfur-containing indicator can be utilized for quality assurance of sulfur-fumigated and non-fumigated Astragali Radix.

Metabolomics data fusion between near infrared spectroscopy and high-resolution mass spectrometry: A synergetic approach to boost performance or induce confusion

In general, data fusion can improve the classification performance of the model, but little attention is paid to the influence of the data fusion on the spatial distribution of the modeling samples. In this paper, the effect of data fusion on sample spatial distribution was studied through integrating NIR data and UHPLC-HRMS data for sulfur-fumigated Chinese herb medicine. Twelve samples collected from four different geographical origins were sulfur fumigated in the lab, and then metabolomics analysis was conducted using NIR and UHPLC-LTQ-Orbitrap mass spectrometer. First of all, the discriminating power of each technique was respectively examined based on PCA analysis. Secondly, combining NIR and UHPLC-HRMS data sets together with or without variable selection was parallelly compared. The results demonstrated that the discriminable ability was remarkably improved after data fusion, indicating data fusion could visualize variable selection and enhance group separation. Samples in the margin between two classes of samples may increase the experience error but has positive effect on the separation direction. Besides, an interesting feature extraction could obtain better discriminable effect than common data fusion. This study firstly provided a new path to employ a comprehensive analytical approach for discriminating SF Chinese herb medicines to simultaneously benefit from the advantages of several technologies.

Structures and Biological Evaluation of Monoterpenoid Glycosides from the Roots of Paeonia lactiflora

Fractionation of an aqueous extract of the air-dried roots of a traditional Chinese medicinal plant, Paeonia lactiflora, yielded the new monoterpenoid glycosides 1-10. Their structures were assigned via spectroscopic techniques, and the absolute configurations of 1, 4-6, and 8 were verified via chemical methods, specific rotation, and electronic circular dichroism data. Compounds 1-4 are rare compared to the reported cage-like paeoniflorin derivatives; that is, they comprised two monoterpenoidal moieties. In the in vitro assay, compounds 5, 8, and 9 showed weak inhibitions against lipopolysaccharide-induced nitric oxide production in RAW264.7 macrophages, with IC₅₀ values of 64.8, 60.1, and 97.5 μM, respectively.

Effects of sulfur-fumigation on the pharmacokinetics, metabolites and analgesic activity of Radix Paeoniae Alba

ETHNOPHARMACOLOGICAL RELEVANCE

Radix Paeoniae Alba (Baishao, BS), one of the most commonly used traditional Chinese medicinal herbs, has many pharmacological effects including analgesic activity. Previous studies found that sulfur-fumigation, a post-harvest handling process developed to prevent mold contamination of medicinal herbs, altered the quality of BS. However, whether sulfur-fumigation affects the pharmacokinetics, safety and efficacy of BS warrants further investigation.

AIM OF THE STUDY

To evaluate the feasibility of sulfur-fumigation as a post-harvest handling process of BS from the viewpoints of pharmacokinetics, safety and efficacy.

MATERIALS AND METHODS

The pharmacokinetic behaviors of four active components of BS and one characteristic component of sulfur-fumigated BS (S-BS) were evaluated by high performance liquid chromatography triple quadrupole mass spectrometry (HPLC-TQ-MS/MS). The safety was investigated using ultra high performance liquid chromatography quadrupole time-of-flight mass spectrometry (UHPLC-QTOF-MS/MS) based metabolomics approach after intragastric (i.g.) administration of non-fumigated BS (N-BS) and S-BS in rats. The analgesic efficacy was compared using hot-plate test in mice, after i.g. administration of N-BS and S-BS, at both high and low dosages.

RESULTS

Systemic exposures of paeoniflorin and oxypaeoniflorin, two analgesic components of BS, were significantly decreased in the S-BS treated group compared to the N-BS treated group, while paeoniflorin sulfonate, one of the sulfur-containing derivatives of S-BS, was detected in all time-points of S-BS treated group with the area under the plasma concentration-time curve (AUC_0-t) and the maximum plasma concentration (C_max) as high as 7077.06 ± 2232.97ng/mL*h and 1641.42 ± 634.79ng/mL respectively, which indicated that sulfur-fumigation altered the pharmacokinetic behaviors of BS. Besides, paeoniflorin sulfonate and its four metabolites with ambiguous toxicities, as well as one endogenous metabolite p-cresol glucuronide, the biomarker of disordered homeostasis of intestinal bacteria and bile acid, were identified as the characteristic metabolites in S-BS administered rats, suggesting that sulfur-fumigation reduced the safety of BS. Furthermore, the analgesic effects at both low and high dosages were decreased in different extent when compared to N-BS administered groups, indicating that sulfur-fumigation weakened the efficacy of BS.

CONCLUSION

Sulfur-fumigation altered the pharmacokinetics, as well as reduced the safety and efficacy of BS, suggesting that sulfur-fumigation is not recommended for post-harvest handling of BS.

Impact of sulphur fumigation on the chemistry of ginger

Ginger (Zingiberis Rhizoma), a commonly-consumed food supplement, is often sulphur-fumigated during post-harvest handling, but it remains unknown if sulphur fumigation induces chemical transformations in ginger. In this study, the effects of sulphur fumigation on ginger chemicals were investigated by ultra-high performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UHPLC-QTOF-MS/MS)-based metabolomics. The results showed that sulphur fumigation significantly altered the holistic chemical profile of ginger by triggering chemical transformations of certain original components. 6-Gingesulphonic acid, previously reported as a naturally-occurring component in ginger, was revealed to be a sulphur fumigation-induced artificial derivative, which was deduced to be generated by electrophilic addition of 6-shogaol to sulphurous acid. Using UHPLC-QTOF-MS/MS extracting ion analysis with 6-gingesulphonic acid as a characteristic chemical marker, all the commercial ginger samples inspected were determined to be sulphur-fumigated. The research outcomes provide a chemical basis for further comprehensive safety and efficacy evaluations of sulphur-fumigated ginger.

Novelty application of multi-omics correlation in the discrimination of sulfur-fumigation and non-sulfur-fumigation Ophiopogonis Radix

A rapid and sensitive approach to differentiate sulfur-fumigated (SF) Ophiopogonis Radix based on Multi-Omics Correlation Analysis (MOCA) strategy was first established. It was characterized by multiple data-acquisition methods (NIR, HPLC, and UHPLC-HRMS) based metabonomics and multivariate statistical analysis methods. As a result, SF and non-sulfur fumigated (NSF) Ophiopogonis Radix samples were efficaciously discriminated. Moreover, based on the acquired HRMS data, 38 sulfur-containing discriminatory markers were eventually characterized, whose NIR absorption could be in close correlation with the discriminatory NIR wavebands (5000–5200 cm⁻¹) screened by NIR metabonomics coupled with SiPLS and 2D-COS methods. This results were also validated from multiple perspectives, including metabonomics analysis based on the discriminatory markers and the simulation of SF ophiopogonin D and Ophiopogonis Radix sample. In conclusion, our results first revealed the intrinsic mechanism of discriminatory NIR wavebands by means of UHPLC-HRMS analysis. Meanwhile, the established MOCA strategy also provided a promising NIR based differential method for SF Ophiopogonis Radix, which could be exemplary for future researches on rapid discrimination of other SF Chinese herbal medicines.

Sulfur fumigation reducing systemic exposure of ginsenosides and weakening immunomodulatory activity of ginseng

ETHNOPHARMACOLOGICAL RELEVANCE

Ginseng (Ginseng Radix et Rhizoma) is used worldwide for its miracle tonic effects, especially for its immunomodulatory activities. Sulfur fumigation, a fast and convenient method to prevent pesticidal and bacterial contamination in the food industry, has been recently employed during post-harvest processing of ginseng. Our previous studies demonstrated that sulfur fumigation significantly altered the chemical profile of the bioactive ingredients in ginseng. However, the effects of sulfur fumigation on the pharmacokinetics and bioactivities of ginseng remain unknown.

AIM OF THE STUDY

To examine the effects of sulfur fumigation on the pharmacokinetics and immunomodulatory activities of ginseng.

MATERIALS AND METHODS

For pharmacokinetic studies, male Sprague-Dawley rats exposed to single/multiple dosages of non-fumigated ginseng (NFG) and sulfur fumigated ginseng (SFG) were investigated using HPLC-MS/MS analysis. For bioactivity studies, male ICR mice were used to compare the immunomodulatory effects of NFG or SFG under both normal and cyclophosphamide (CY)-induced immunocompromised conditions using white blood cell counts, serum cytokine levels, and spleen and thymus weight indices.

RESULTS

Sulfur fumigation significantly reduced the contents of the bioactive ginsenosides in ginseng, which resulted in drastically low systemic exposure of ginsenosides in SFG-treatment group compared to NFG-treatment group. This observation was consistent with the bioactivities obtained in NFG- and SFG-treatment groups. The bioactivity studies also demonstrated the immunomodulatory effects of NFG but not SFG in the CY-induced immunosuppressed mice.

CONCLUSION

Sulfur fumigation significantly reduced contents of bioactive ginsenosides in ginseng, leading to dramatic decrease in the systemic exposure of these ginsenosides in the body and detrimental reduction of immunomodulatory effects of ginseng. Our results provided scientific evidences and laid a solid foundation for the needs of thorough evaluation of the significant impact of sulfur fumigation on ginseng and other medicinal herbs.

1-Acyl-3-O-[β-glucopyranosyl-(1″→6′)-β-glucopyranosyl]-glycerols and Cordycedipeptides B and C, New Metabolites from Bacillus pumilus

Four 1-monoacyl-3- O-[β-glucopyranosyl-(1→6)-β-glucopyranosyl]-glycerols (1) and four 1,2-diacyl-3- O-[β-glucopyranosyl-(1→6)-β-glucopyranosyl]-glycerols (2a) with acyl residues consisting of 1:1 mixtures of 1- iso-pentadecanoyl- and 1- anteiso-pentadecanoyl residues and the respective heptadecanoic acid isomers s as main components, have been characterized in the extracts of Bacillus pumilus strain DKS1. Twenty-seven further metabolites, among them the diketopiperazines cordycedipeptide A (3), B (4), and C (5), were obtained. All compounds were elucidated by NMR and MS techniques and fully characterized and tested for antimicrobial activity against Legionella pneumophila.

Evaluation of the Influence of Sulfur-Fumigated Paeoniae Radix Alba on the Quality of Si Wu Tang by Chromatographic and Chemometric Analysis

An accurate and reliable method of high-performance liquid chromatographic fingerprint combining with multi-ingredient determination was developed and validated to evaluate the influence of sulfur-fumigated Paeoniae Radix Alba on the quality and chemical constituents of Si Wu Tang. Multivariate data analysis including hierarchical cluster analysis and principal component analysis, which integrated with high-performance liquid chromatographic fingerprint and multi-ingredient determination, was employed to evaluate Si Wu Tang in a more objective and scientific way. Interestingly, in this paper, a total of 37 and 36 peaks were marked as common peaks in ten batches of Si Wu Tang containing sun-dried Paeoniae Radix Alba and ten batches of Si Wu Tang containing sulfur-fumigated Paeoniae Radix Alba, respectively, which indicated the changed fingerprint profile of Si Wu Tang when containing sulfur-fumigated herb. Furthermore, the results of simultaneous determination for multiple ingredients showed that the contents of albiflorin and paeoniflorin decreased significantly (P < 0.01) and the contents of gallic acid and Z-ligustilide decreased to some extent at the same time when Si Wu Tang contained sulfur-fumigated Paeoniae Radix Alba. Therefore, sulfur-fumigation processing may have great influence on the quality of Chinese herbal prescription.

Sulfur dioxide residue in sulfur-fumigated edible herbs: The fewer, the safer?

The residual content of sulfur dioxide is frequently regarded as the exclusive indicator in the safety evaluation of sulfur-fumigated edible herbs. To examine the feasibility of such assessment criteria, here the variations in residual sulfur dioxide content during sulfur-fumigation and the potential mechanisms involved were investigated, using Angelicae Sinensis Radix (ASR) as a model herb. The residual sulfur dioxide content and ten major bioactive components in sulfur-fumigated ASR samples were dynamically examined at 13 successive time points within 72 h sulfur-fumigation. The relationship between the content variation tendency of sulfur dioxide and the ten chemicals was discussed. The results suggested that sulfur dioxide-involved chemical transformation of the original components in ASR might cause large consumption of residual sulfur dioxide during sulfur-fumigation. It implies that without considering the induced chemical transformation of bioactive components, the residual sulfur dioxide content alone might be inadequate to comprehensively evaluate the safety of sulfur-fumigated herbs.

Influence of sulfur fumigation on the chemical constituents and antioxidant activity of buds of Lonicera japonica

Lonicera japonica flos is widely used as a pharmaceutical resource and a commonly-employed ingredient in healthy food, soft beverages and cosmetics in China. Sometimes, sulfur fumigation is used during post-harvest handling. In this study, a comprehensive comparison of the chemical profile between sun-dried and sulfur-fumigated samples was conducted by HPLC fingerprints and simultaneous quantification of nine constituents, including secologanic acid, along with another eight usually-analyzed markers. Secologanic acid was destroyed, and its sulfonates were generated, whereas caffeoylquinic acids were protected from being oxidized. The residual sulfur dioxide in sulfur-fumigated samples was significantly higher than that in sun-dried samples, which might increase the potential incidence of toxicity to humans. Meanwhile, compared with sun-dried samples, sulfur-fumigated samples have significantly stronger antioxidant activity, which could be attributed to the joint effect of protected phenolic acids and flavonoids, as well as newly-generated iridoid sulfonates.

Study on the effects of sulfur fumigation on chemical constituents and antioxidant activity of Chrysanthemum morifolium cv. Hang-ju

The traditional after-harvesting drying method of C. morifolium cv. Hang-ju (HJ) is sun drying, but recently sulfur fumigation is increasingly used as a cheap and convenient method. However, the effects of sulfur fumigation on chemical constituents and potential activities of HJ were unknown. A comprehensively comparison of the chemical profiles between non-fumigated HJ (NHJ) and sulfur-fumigated HJ (SHJ) was conducted by HPLC fingerprints analysis and the discrepant peaks were identified or tentatively assigned by HPLC-ESI/MS(n). Dramatic chemical changes were found that the contents of 4 flavonoid aglycones remarkably increased while those of 7 glycosides significantly reduced which suggested that sulfur-fumigation induced flavonoid glycosides transformed into aglycons by hydrolysis reaction. A significant loss of hydroxycinnamoylquinic acids showed the sulfur fumigation was a destructive effect on HJ. Principal component analysis (PCA) was employed to rapidly discriminate NHJ and SHJ samples. By ICP-OES analysis, it was found that the residue of sulfur of SHJ were three times higher than NHJ (p<0.05). The antioxidant activity of NHJ and SHJ were evaluated by DPPH and FRAP assay, and the results showed that NHJ had much stronger antioxidant activities than SCF (p<0.05). Combining the results of chemical analysis, residue of sulfur and pharmacological evaluation, it showed that the sulfur fumigation was a destructive effect on HJ.

Sulfur fumigation, a better or worse choice in preservation of Traditional Chinese Medicine?

Sulfur fumigation (SF) in Traditional Chinese Medicine (TCM) is a highly efficient and important traditional preservation method in China. This method has generated a great deal of concern and has been disputed in the last few years because of its uncertain safety. SF can alter the quality of TCMs by damaging the bioactive compounds, changing chemical profiles, and generating detrimental exogenous materials. However, SF is still widely used in the herbal medicinal industry because of its various benefits, such as its pesticidal and anti-bacterial effects, easy operation, and low-cost. This review contains the current situation, chemical mechanism and reactions during SF, the pharmacological and pharmacokinetic research, and the influence of quality caused by SF. In addition, a quantification-operation sulfur fumigation device (QOSFD), which can maintain the quality of TCMs by controlling the SF processing parameters, has been designed and introduced. The key technologies of this device involve controlling the O(2) content and the temperature of SO(2) as well as the quantification of sulfur in SF. This device can reduce the possibility of reaction between bioactive compounds and sulfur/sulfurous acid, as well as control the limitation of SO(2) residues. The QOSFD is regarded as a promising preservation technique in the field of TCM, medicinal materials, agriculture, and fruit industry.

β-D-Arabinosyl 1-C-sulfonic acid. J Sulphur Chem 2013;34:33-37. [PMID: 28966658 DOI: 10.1080/17415993.2012.706814] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

A short synthetic route to β,d-arabinofuranosyl 1-C-sulfonic acid (7), a possible biomimetic for the arabinofuranosyl anomeric phosphate, is described. The furanosyl 1-C-sulfonate was prepared by buffered DMDO oxidation of an S-acetyl-1-thio-β-arabinofuranose derivative. Deprotection under mild conditions allowed isolation of the free sulfonic acid without desulfonylation.

Detection of sulfur-fumigated Paeoniae Alba Radix in complex preparations by high performance liquid chromatography tandem mass spectrometry

Detection of sulfur-fumigated Paeoniae Alba Radix (PAR) in different complex preparations is challenging due to the relatively lower content of PAR and interference from more complicated components in complex preparations with different multiple constituent herbs. In this study, a high performance liquid chromatography- triple-quadrupole tandem mass spectrometry method was developed for detecting sulfur-fumigated PAR in different complex preparations. Paeoniflorin, the major component of PAR, and paeoniflorin sulfonate, the characteristic artifact transformed from paeoniflorin during sulfur-fumigation of PAR, were used as chemical markers. Multiple reaction monitoring (MRM) scan was employed to maximize sensitivity and selectivity. Through optimizing full mass scan and daughter ion scan conditions, two mass transitions were selected and employed respectively for unequivocal identification of paeoniflorin and paeoniflorin sulfonate. The detection limits for paeoniflorin and paeoniflorin sulfonate using MRM were much lower than those detected with UV 270 nm. Paeoniflorin and paeoniflorin sulfonate could be simultaneously detected in different commercial PAR-containing complex preparations without interference of other components using the established method, indicating that the newly established method was selective and sensitive enough for screening sulfur-fumigated PAR in commercial complex preparations.

Pharmacokinetic comparisons of typical constituents in white peony root and sulfur fumigated white peony root after oral administration to mice

AIM

White peony root and sulfur fumigated white peony root are produced by different processing methods from the root of Paeonia lactiflora Pall, but the two traditional Chinese medicines are used under the same common name white peony root. In order to clarify the influence of sulfur fumigation on pharmacokinetics of the main monoterpene glucoside components in white peony root, an investigation was carried out to compare the pharmacokinetics of sodium paeoniflorin sulfonate (1) and paeoniflorin (2), benzoylpaeoniflorin sulfonate (3) and benzoylpaeoniflorin (4), as well as 1 in sulfur fumigated white peony root extract (SWPE) and 2 in white peony root extract (WPE).

MATERIALS AND METHODS

A high-performance liquid chromatographic (HPLC) assay was developed to determine the plasma concentrations of the four analytes. Kunming species of mice were orally administered the four compounds and the two extracts with approximately the same dose.

RESULTS

It was found that C(max) and AUC of 1 and 3 were increased (P<0.05), and the T(max) and t(1/2) were prolonged (P<0.05) by comparison with that of 2. Similar results were also observed for the pharmacokinetics parameters of 1 in SWPE and 2 in WPE. However, benzoylpaeoniflorin (4) was not detected in plasma collected at certain intervals after administered orally to mice.

CONCLUSIONS

These results indicate that sulfonation of the monoterpene components could improve the bioavailability and delay the absorption of them in mice.

Monoterpenes from Paeonia albiflora and their inhibitory activity on nitric oxide production by lipopolysaccharide-activated microglia

Eleven new monoterpenes, paeonidangenin (1), paeonidanin A (2), paeonidanin B (3), paeonidanin C (4), paeonidanin D (5), paeonidanin E (6), paeoniflorone (7), 4-O-methylbenzoylpaeoniflorin (8), 4-O-methylgalloylpaeoniflorin (9), 4-O-methyldebenzoylpaeoniflorin (10), and 4-O-methylalbiflorin (11), were isolated from the 60% ethanol extract of the roots of Paeonia albiflora. Their structures were determined primarily on the basis of 1D and 2D NMR techniques and MS studies. Paeonidanins D (5) and E (6) are unprecedented examples of "cage-like" monoterpene dimers. The inhibitory effects of the isolated compounds on nitric oxide production by lipopolysaccharide (LPS)-activated N9 microglia were evaluated.

Two new monoterpene glucosides from Paeonia lactiflora Pall

Two new monoterpene glucosides, 4'-O-benzoylpaeoniflorin (1) and 4-O-galloylalbiflorin (2), were isolated from the 60% ethanol extract of the dried roots of Paeonia lactiflora Pall. Their structures were established on the basis of spectroscopic data.

Liquid chromatography/mass spectrometry analysis of PHY906, a Chinese medicine formulation for cancer therapy

PHY906 is a Chinese medicine formulation prepared from four medicinal herbs for adjuvant cancer chemotherapy. In this paper, liquid chromatography/electrospray ionization time-of-flight mass spectrometry (LC/ESI-TOFMS) was used to clarify the chemical composition of PHY906. The aqueous extract of PHY906 was separated on a Waters Atlantis C(18) column, and was eluted with acetonitrile/0.05% (v/v) formic acid. The separated compounds were identified with pure standards, or tentatively characterized by analyzing their mass spectra recorded in both negative and positive ion polarity modes. Further structural information was obtained from in-source fragmentation. Based on the LC/MS analysis, we proposed the structures for 64 bioactive compounds, including flavonoids, triterpene saponins, and monoterpene glycosides. All the compounds identified from PHY906 were further assigned in the four individual herbs, and some of them are reported for the first time.

RP-HPLC detection of a sulphiting-induced artefact from paeoniflorin in dried roots of Paeonia lactiflora

Paeoniflorin is one of the bioactive ingredients of the roots of Paeonia lactiflora (Paeoniaceae). A comparative study of processed and non-processed commercial samples of dried roots of P. lactiflora indicated a very low level of paeoniflorin in the processed sample and the formation of a new more polar component, sodium paeoniflorin sulphonate, during treatment of the roots with sulphiting agents.