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• W2140333559 abstract "We previously identified vitamin B6 deficiency in a child presenting with seizures whose primary diagnosis was the inherited disorder hyperprolinemia type II. This is an unrecognized association, which was not explained by diet or medication. We hypothesized that pyridoxal phosphate (vitamin B6 coenzyme) was de-activated by l-Δ1-pyrroline-5-carboxylic acid, the major intermediate that accumulates endogenously in hyperprolinemia type II. The proposed interaction has now been investigated in vitro with high resolution 1H nuclear magnetic resonance spectroscopy and mass spectrometry at a pH of 7.4 and temperature of 310 K. Three novel adducts were identified. These were the result of a Claisen condensation (or Knoevenagel type of reaction) of the activated C-4 carbon of the pyrroline ring with the aldehyde carbon of pyridoxal phosphate. The structures of the adducts were confirmed by a combination of high performance liquid chromatography, nuclear magnetic resonance, and mass spectrometry. This interaction has not been reported before. From preliminary observations, pyrroline-5-carboxylic acid also condenses with other aromatic and aliphatic aldehydes and ketones, and this may be a previously unsuspected generic addition reaction. Pyrroline-5-carboxylic acid is thus found to be a unique endogenous vitamin antagonist. Vitamin B6 de-activation may contribute to seizures in hyperprolinemia type II, which are so far unexplained, but they may be preventable with long term vitamin B6supplementation. We previously identified vitamin B6 deficiency in a child presenting with seizures whose primary diagnosis was the inherited disorder hyperprolinemia type II. This is an unrecognized association, which was not explained by diet or medication. We hypothesized that pyridoxal phosphate (vitamin B6 coenzyme) was de-activated by l-Δ1-pyrroline-5-carboxylic acid, the major intermediate that accumulates endogenously in hyperprolinemia type II. The proposed interaction has now been investigated in vitro with high resolution 1H nuclear magnetic resonance spectroscopy and mass spectrometry at a pH of 7.4 and temperature of 310 K. Three novel adducts were identified. These were the result of a Claisen condensation (or Knoevenagel type of reaction) of the activated C-4 carbon of the pyrroline ring with the aldehyde carbon of pyridoxal phosphate. The structures of the adducts were confirmed by a combination of high performance liquid chromatography, nuclear magnetic resonance, and mass spectrometry. This interaction has not been reported before. From preliminary observations, pyrroline-5-carboxylic acid also condenses with other aromatic and aliphatic aldehydes and ketones, and this may be a previously unsuspected generic addition reaction. Pyrroline-5-carboxylic acid is thus found to be a unique endogenous vitamin antagonist. Vitamin B6 de-activation may contribute to seizures in hyperprolinemia type II, which are so far unexplained, but they may be preventable with long term vitamin B6supplementation. pyridoxal phosphate l-Δ1-pyrroline-5-carboxylic acid mass spectrometry gas chromatography high performance liquid chromatography sodium-3-trimethylsilyl-1-[2,2,3,3-2H4]propionate CH3CN trimethylsilyl diffusion ordered spectroscopy nuclear Overhaüser enhancement heteronuclear multiple-quantum correlation heteronuclear multiple-bond correlation total correlation spectroscopy radio frequency, noesypresat, nuclear Overhaüser enhancement spectroscopy pre-saturation Vitamin B6 (pyridoxine and related compounds) is distributed widely in food (1György, P., The Vitamins, 2nd Ed., Sebrell, W. H., Harris, R. S., II, 1968, 90, 104, Academic Press, Inc., New York.Google Scholar, 2McCoy E.E. Dolphin D. Poulson R. Avramovic O. Coenzymes and Cofactors Vol. I Vitamin B6. Pyridoxal Phosphate. Part B. John Wiley and Sons, Inc., New York1986: 573-600Google Scholar). Severe nutritional deficiency is not common in humans (3Bates C.J. Ann. Clin. Biochem. 1997; 34: 599-626Crossref PubMed Scopus (60) Google Scholar) and has generally arisen in unusual circumstances. Most reports were in the early 1950s and described babies who presented with seizures after being fed with processed milks lacking the vitamin for over 2 months (4Tryfiates G.P. Dolphin D. Poulson R. Avramovic O. Coenzymes and Cofactors Vol. I Vitamin B6. Pyridoxal Phosphate. Part B. John Wiley and Sons, Inc., New York1986: 421-447Google Scholar). Deficiency has also developed during treatment with drugs that de-activate or antagonize the vitamin, causing dermatitis, seizures, or neuropathy (2McCoy E.E. Dolphin D. Poulson R. Avramovic O. Coenzymes and Cofactors Vol. I Vitamin B6. Pyridoxal Phosphate. Part B. John Wiley and Sons, Inc., New York1986: 573-600Google Scholar, 4Tryfiates G.P. Dolphin D. Poulson R. Avramovic O. Coenzymes and Cofactors Vol. I Vitamin B6. Pyridoxal Phosphate. Part B. John Wiley and Sons, Inc., New York1986: 421-447Google Scholar, 5Holtz P. Palm D. Pharmacol. Rev. 1964; 16: 113-178PubMed Google Scholar, 6Sauberlich, H. E., The Vitamins, 2nd Ed., Sebrell, W. H., Harris, R. S., II, 1968, 33, 44, Academic Press, Inc., New York.Google Scholar, 7Alvarez F.G. Guntupalli K.K. Intensive Care Med. 1995; 21: 641-644Crossref PubMed Scopus (66) Google Scholar). This analytical study was prompted by finding vitamin B6 deficiency in a child with hyperprolinemia type II (genetic classification McKusick 23591, Online Mendelian Inheritance in Man, available on the Web), a rare inherited disorder due to lack of the enzyme Δ1-pyrroline-5-carboxylate dehydrogenase (EC 1.5.1.12) (8Phang J.M. Yeh G.C. Scriver C.R. Scriver C.R. Beaudet A.L. Sly W.S. Valle D. The Metabolic and Molecular Bases of Inherited Disease. McGraw-Hill, Inc., New York1995: 1125-1146Google Scholar) (Fig. 1). This association has not been reported before. Full clinical details of the case and diagnostic biochemistry have been reported previously (9Walker V. Mills G.A. Peters S.A. Merton W.L. Arch. Dis. Child. 2000; 82: 236-237Crossref PubMed Scopus (28) Google Scholar). In brief, a previously healthy girl presented at 20 months of age with prolonged seizures and depressed conscious level in association with pneumonia. She was well nourished and usually had a normal mixed diet. Abnormalities of plasma and urine biochemistry were diagnostic of hyperprolinemia type II (8Phang J.M. Yeh G.C. Scriver C.R. Scriver C.R. Beaudet A.L. Sly W.S. Valle D. The Metabolic and Molecular Bases of Inherited Disease. McGraw-Hill, Inc., New York1995: 1125-1146Google Scholar). Plasma proline was 2690 μm (reference range 90–280 μm) and has remained high since (2290–2955 μm, six observations over 2 years). She recovered slowly over 5 days and was then healthy, except for a severe diaper rash during convalescence. Xanthurenic acid was found in her urine organic acid profile at presentation. We have not seen this tryptophan metabolite in other children's urine, and it indicated the possibility of vitamin B6 deficiency (1György, P., The Vitamins, 2nd Ed., Sebrell, W. H., Harris, R. S., II, 1968, 90, 104, Academic Press, Inc., New York.Google Scholar, 2McCoy E.E. Dolphin D. Poulson R. Avramovic O. Coenzymes and Cofactors Vol. I Vitamin B6. Pyridoxal Phosphate. Part B. John Wiley and Sons, Inc., New York1986: 573-600Google Scholar, 4Tryfiates G.P. Dolphin D. Poulson R. Avramovic O. Coenzymes and Cofactors Vol. I Vitamin B6. Pyridoxal Phosphate. Part B. John Wiley and Sons, Inc., New York1986: 421-447Google Scholar, 5Holtz P. Palm D. Pharmacol. Rev. 1964; 16: 113-178PubMed Google Scholar). We confirmed this by finding marginally low plasma pyridoxal phosphate concentrations (23.5 and 22.7 μm; reference range 24.3–81.0 μm) and barely detectable pyridoxic acid (1.0 and 2.7 μm, reference range 10.9–27.3 μm) in her plasma on two occasions when she was well (3 and 8 months after her illness) and a grossly abnormal response to tryptophan loading at 8 months after presentation (9Walker V. Mills G.A. Peters S.A. Merton W.L. Arch. Dis. Child. 2000; 82: 236-237Crossref PubMed Scopus (28) Google Scholar). The deficiency was not nutritional or due to ingestion of antagonistic drugs. We therefore proposed that the vitamin was de-activated by an interaction between pyridoxal phosphate (PP)1 (Structure FT1), the active coenzyme form of vitamin B6 (the keto [1k] tautomer), and l-Δ1-pyrroline-5-carboxylic acid (P5C) (Structure FT2), the intermediate which accumulates in hyperprolinemia type II. (Structures FT1 and FT2). There was some foundation for this, because a chemical test for P5C is based on its reaction with 2-aminobenzaldehyde (10Vogel H.J. Davis B.D. J. Am. Chem. Soc. 1952; 74: 109-122Crossref Scopus (91) Google Scholar). This reagent, like pyridoxal phosphate, is an aromatic aldehyde. We have now investigated the proposed interaction in vitro using mass spectrometry (MS) and high resolution 1H nuclear magnetic resonance (NMR) spectroscopy. Preliminary NMR and high performance liquid chromatography-mass spectrometry (HPLC-MS) studies confirmed a reaction between PP and P5C co-incubated in aqueous solution at physiological pH (7.4) and temperature (310 K). Three adducts were produced, which we have characterized and found to be novel. They result from a Claisen condensation (or Knoevenagel type of reaction) involving the pyridoxal phosphate carbonyl group and the activated C-4 carbon of the pyrroline ring. This reaction has not been reported before. The most common type of in vivo enzymatic reaction of PP is in transamination, the transfer of an α-amino group of an amino acid to the α-carbon atom of an α-keto acid (5Holtz P. Palm D. Pharmacol. Rev. 1964; 16: 113-178PubMed Google Scholar, 11Vogel, H. J., and Davis, B. D. (1952) J. Am. Chem. Soc. 74, 109-122Google Scholar). These reactions are reversible and involve the formation of Schiff bases as intermediates. Therefore, P5C is a unique endogenous pyridoxal phosphate antagonist. If this condensation occurs in vivo, as we propose, individuals with hyperprolinemia type II would have an increased vitamin B6requirement and be at risk of symptomatic deficiency. In preliminary observations we find that P5C also reacts with a range of aliphatic aldehydes and ketones and benzaldehyde at physiological pH. This condensation may be a newly recognized general reaction with activated carbonyls. dl-Δ1-Pyrroline-5-carboxylic acid, 2,4-dinitrophenylhydrazine hydrochloride double salt, pyridoxal-5-phosphate, pyridoxamine dihydrochloride, 4-pyridoxic acid, pyridoxine, and pyridoxal hydrochloride were from Sigma, and acetophenone (99% pure), benzaldehyde, and aliphatic aldehydes were from Aldrich (Sigma-Aldrich Company Ltd., Poole, UK). Deuterium oxide (D2O), deuterium chloride (DCl), and sodium deuteroxide (NaOD) were from Goss Scientific Instruments Ltd., Great Baddow, UK. Sodium-3-trimethylsilyl-1-[2,2,3,3-2H4]propionate (TSP) was from Fluorochem Ltd., Old Glossop, Derbyshire, UK, and diethyl ether (Analar) from BDH, Poole, Dorset, UK. Glassware for P5C preparation was acid-washed. The P5C was prepared from its 2,4-dinitrophenylhydrazine hydrochloride double salt, using a method based on that of Mezl and Knox (12Mezl V.A. Knox W.E. Anal. Biochem. 1976; 74: 430-434Crossref PubMed Scopus (141) Google Scholar) but modified by using a more concentrated starting solution of the hydrazine and a diethyl ether wash instead of toluene to remove excess acetophenone. Preparations made according to the published method were found by NMR to be contaminated with toluene and acetophenone, and P5C was polymerized. Thus a slightly modified method was adopted. To 40 mg of the hydrazine in a glass tube were added 2.0 ml of 0.25 m DCl and 8 ml (0.2 ml/mg hydrazine) of acetophenone. The mixture was shaken on a roller mixer for 30 min in a cold room at 4 °C. After centrifugation, the lower aqueous layer was transferred to a clean tube and washed with ∼8 ml of diethyl ether five times to remove acetophenone. Ether was removed from the aqueous extract by evaporation under nitrogen at room temperature. After adjusting the pH to 7.4 with NaOD, the extract was stored at 4 °C. NMR confirmed P5C to be present, with no evidence of polymerization or contamination with acetophenone. This is the first report of the NMR spectrum of P5C (shown in Fig. 3 B). Contrary to expectation (12Mezl V.A. Knox W.E. Anal. Biochem. 1976; 74: 430-434Crossref PubMed Scopus (141) Google Scholar) we found that P5C was reasonably stable under these conditions, with no evidence of polymerization after 4 weeks of storage at room temperature. Different batches showed varying rates of degradation, and after 3 months each batch had degraded by ∼50–70% to a complex mix of monomeric substances. Pyridoxal phosphate (PP) (5 mg/ml in D2O) was adjusted to pH 7.4 with NaOD, protected from light, and stored at 4 °C. NMR (see Fig. 3 A) confirmed the purity of the preparation and the 4:1 ratio of the keto to enol forms. Incubates of P5C and PP were prepared in two ways. In the earlier experiments, 250 μl of stock P5C was added to 5 mg of PP (solid) in a vial, the pH was adjusted immediately to 7.4 with NaOD, D2O was added to a volume of 1.5 ml, and the pH was readjusted to 7.4. In later experiments, aliquots of stock solutions of P5C and PP, both prepared at pH 7.4, were mixed and diluted appropriately with D2O, and the pH was readjusted to 7.4. The method of preparation did not influence the products of co-incubation. After incubation at 310 K for 24 h, the mixture was analyzed, initially using HPLC-MS (Fig. 2) and then NMR (Fig. 3 C, around 36 h after mixing). The solution was found to be reacting slowly at ambient temperature, and the reaction was monitored by 1H NMR over a period of 12 days. The mixture was then characterized by MS and1H NMR and heteronuclear NMR, including1H-13C correlation experiments HMQC and HMBC at 14.1 tesla (T) and 17.6 T. In addition, diffusion (13Stejskal E.O. Tanner J.E. J. Chem. Phys. 1965; 42: 288-292Crossref Scopus (6728) Google Scholar) and gradient nOe experiments (14Stott K. Keeler J. Van Q.N. Shaka A.J. J. Magn. Reson. 1997; 125: 302-324Crossref Scopus (407) Google Scholar) were employed to distinguish the various components in the mixture. The structures were further confirmed by HPLC-NMR-MS. The mass spectra were obtained under positive and negative ionization conditions on a Micromass Platform II electrospray HPLC-MS system. The HPLC was carried out on an HP1100 (Hewlett Packard) system using a reverse phase C18 column (Phenomenex 100 × 2.0 mm) at ambient temperature. The eluents were water and acetonitrile with 0.1% formic acid added as an ion-pairing agent. An 8-min gradient from 100% water to 100% acetonitrile was employed, and the fractions were observed using a UV diode array detector followed by MS. Experiments were carried out at 750.3 MHz (1H) and 188.7 MHz (13C) on a Varian INOVA 750 (17.6 T) spectrometer and at 600.13 MHz (1H), 150.9 MHz (13C), and 242.9 MHz (31P) on a Bruker DRX600 (14.1 T) spectrometer. To 500 μl of each sample in a 5-mm NMR tube, 10 μl (10 μg) of 0.1% w/v TSP in D2O was added to enable accurate quantification and act as an internal shift reference. The one-dimensional 1H NMR experiments were carried out under conditions of full relaxation and good digitization to enable reasonable integration for quantification. The 90° pulses used were calibrated after tuning and matching the rf for each sample at the temperatures for which different measurements were taken. Typically 65,536 data points were acquired over a 16.02-ppm (9614 Hz at 600 MHz) spectral width or 131,072 data points over 16.0 ppm (12,001 Hz at 750 MHz) using a noesypresat (15Nicholson J.K. Foxall P.J.D. Spraul M. Farrant R.D. Lindon J.C. Anal. Chem. 1995; 67: 793-811Crossref PubMed Scopus (934) Google Scholar) solvent suppression pulse sequence. A mixing time of 100 ms, together with 3 s of presaturation and an acquisition time of 3.4 s at 600 MHz or 5.3 s at 750 MHz, was employed. The gradient nOe experiments were done at 750 and 600 MHz using the same respective data tables as above, with mix times of 0.8–1 s and gradient ratios of 35:5:3:2:1 and from 2000 to 8000 transients per experiment. The diffusion experiments (Fig.4) were acquired as above at 750 MHz with the diffusion time fixed at 0.5 s. The gradient strength was ramped successively from 0.5 to 30.5 gauss/cm in increments of 2 gauss with 16 experiments each of 64 transients acquired with a repetition time of 5 s per transient. Two-dimensional experiments TOCSY, HMQC, and HMBC were run at 750 MHz and 310 K (nominal, actual temperature was 311.4 K) in phase-sensitive mode, typically 2048 (or 4096 for HMBC) data points acquired over a 13-ppm spectral width in F2 (and F1 for the TOCSY homonuclear experiment), the proton dimension, and 200 ppm in F1 for the carbon dimension. The TOCSY experiment was carried out with 32 transients for each of 256 increments using a spin lock period of 60 ms and a relaxation delay of 1.5 s, during which the HOD signal was pre-saturated to reduce the dynamic range. A total of 256 transients at a pulse repetition rate of 0.5 s per scan for each of 128 increments in the HMQC, and 440 transients (pulse repetition rate equal to 1.5 s) for 256 increments in the HMBC experiment were employed. Globally optimized alternating-phase rectangular decoupling of the carbon frequencies was employed in the HMQC experiment. Cosine window functions were used in the F2 (acquisition dimension) and linear prediction to 1024 complex data points (coefficients optimized for each experiment) with no window function applied in the F1 dimension, prior to Fourier transformation. The phosphorus spectra were acquired at 242.9 MHz (14.1 T) with and without proton decoupling {1H} using 65,536 data points over 50 ppm with 640 transients for both experiments, employing 90° pulses at a pulse repetition time of 4.7 s. An external reference of phosphoric acid was used for calibration and set to 0 ppm. A line broadening of 1 Hz was used in the exponential multiplication window function to increase the apparent signal to noise prior to Fourier transformation. The carbon spectra were acquired with Waltz-16 (12̄3) decoupling of the protons. A 250 ppm spectral width with 131,072 data points and 102,000 transients (51 h) at a repetition rate per scan of 1.8 s yielded a low signal-to-noise spectrum at 150 MHz. The sample was concentrated to 160 μl of volume and run on a 3-mm dual 13C/1H probe at 188.69 MHz. After 40,000 transients at 310 K (nominal, actual temperature was 311.8 K) and a pulse repetition time of 2 s, the spectrum shown as the F1 projection trace in Fig.5 was obtained. With gradient elution, HPLC-NMR was carried out using a Bruker LC-22 HPLC system. The mobile phase was pumped at 1 ml/min through a C18 reverse phase column (Phenomenex 250 × 4.6 mm) at 25 °C. The eluents were D2O and CH3CN (ACN) each with 0.05% trifluoroacetic acid added, starting with 100% D2O decreasing to 60% D2O and 40% ACN over 25 min, followed by a 2-min 100% ACN purge flush before returning to 100% D2O. The eluting fractions were detected by UV (Bischoff Lambda 1000) at 254 nm, and the absorption was used as a delayed trigger to stop the pump when the fraction had flowed into the NMR probe cell. The 1H NMR at 600 MHz was measured while the flow was stopped. The pulse sequence was noesypresat with double-solvent suppression and ACN 13C satellite decoupling. A selective-shaped rf pulse was employed, with frequency adjusted to the ACN at the center of the spectrum (2 ppm also used as internal reference) and to the residual HOD signal, which reduced its shift value with increasing ACN concentration during the gradient elution. Shape selective gradient shimming of the ACN signal was used to maximize the magnetic field homogeneity. The number of transients taken varied from 128 to 1024 for the different fractions, prior to continuing the HPLC pump and moving on to the next peak in the UV. The number of scans depended upon the fraction's concentration and the signal-to-noise ratio achieved between 5 and 11 ppm. Each fraction was collected post-NMR using a Foxy Junior fraction collector and was then run on a Micromass Platform Q-TOF in positive ion electron impact conditions for accurate mass measurement. Erythromycin was co-injected, and the ion atm/z = 734.4690 used as the lock reference mass. The initial analysis was by MS of the mixture, arising from a 24-h incubation at 310 K of 1 ml of P5C and 1 ml of PP solution (Fig. 2). Three new quasimolecular ions (M − H)− were observed at m/z = 297, 341, and 359 Da by negative ion electrospray, in addition to the expected quasimolecular ions for P5C at m/z = 112 and PP atm/z = 246 Da. The initial 1H NMR spectrum at 600 MHz (Fig. 3 C, after 36 h of reaction) of the same solution at 298 K showed several products in addition to the two starting components. In an attempt to analyze these components in situ, while the reaction was still ensuing, a series of diffusion (13Stejskal E.O. Tanner J.E. J. Chem. Phys. 1965; 42: 288-292Crossref Scopus (6728) Google Scholar) experiments were conducted at 750 MHz for maximum shift dispersion. The mixture was partially resolved into its component parts, termed Diffusion Ordered SpectroscopY (DOSY) (16Gibbs S.J. Johnson Jr., C.S. J. Magn. Reson. 1991; 93: 395-402Google Scholar, 17Barjat H. Morris G.A. Smart S. Swanson A.G. Williams S.C.R. J. Magn. Reson. Ser. B. 1995; 108: 170-172Crossref Scopus (205) Google Scholar) as illustrated in Fig. 4. The technique relies upon the individual species having different diffusion coefficients, which often vary with the size of the molecule. Hence, for neutral compounds, a separation of each compound's spectrum along the diffusion axis occurs with increasing molecular mass. However, if there is molecular association of any kind, the diffusion coefficient of the associated components will change and the above progression no longer holds. The products were obviously the result of reaction of P5C and PP, because signals with similar shifts and couplings were observed. The question was, what structures did they have? The lack of any additional aldehyde proton signals around 9.5–10.5 ppm indicated that reaction had occurred at that site on the PP. The appearance of a finely coupled triplet of doublets at δ 6.93 suggested an olefinic proton with three remote coupling partners. A series of one-dimensional TOCSY experiments established that these were a pair of double, double doublets (ddd) at δ 2.36 and δ 2.75 and a finely coupled doublet at δ 8.09. The former were a geminal methylene pair and the latter an olefinic proton β to a hetero-atom, similar to H5 in P5C. These signals, when carefully integrated and compared with the signal at δ 6.93, were present at equimolar equivalents to one another. The diffusion spectra revealed that a significant set of signals was hidden under the water signal at δ 4.77. The sample was therefore heated to 310 K, causing the water signal to shift to a higher field and the multiplets thus became observable in the one-dimensional noesypresat spectrum. They integrated for a total of three protons when compared with the new doublet at δ 8.09. At this point a series of heteronuclear experiments were measured, first on 31P to establish the presence of the phosphate group. Three clearly distinguishable triplets were observed, the largest at the lowest field δ 5.19 was attributed to the unreacted PP. The other two triplets at δ 5.02 and δ 5.08 were clearly new phosphate-containing molecules. Other signals were present but were overlapped by the major and minor components or at too low a concentration to be observed at the signal-to-noise level achieved. The next step involved acquisition of an HMQC and HMBC1H-13C correlated set of two-dimensional spectra (Fig. 5). The identity of the reaction products was deduced by combination of the two data sets. The coupled network of five carbons connected to the geminal methylene pair corroborated the earlier one-dimensional evidence and confirmed the olefinic functionality. The possibilities for the reaction products were thus narrowed down to one site of reaction on the P5C, namely the C-4 carbon. The other possibilities arising from either isomers of P5C or the ring opened form dl-glutamic-γ-semialdehyde (the latter would involve addition of the amine to the aldehyde of PP to form a Schiff base) were all excluded on the basis of the coupling network observed from the TOCSY and HMBC experiments. The proposed new Structures 3a and 3b would have resulted from an addition of the C-4 carbon to the aldehyde of PP, reminiscent of the Knoevenagel reaction, with the imine function of P5C behaving like the carbonyl in the more usual ketone-aldehyde reaction. Following the condensation, elimination of water formed an olefin with two possible stereoisomers, one of which turned out to be the major product with a molecular mass of 342 Da. Distinction between these isomers was achieved using double-pulse field gradient nOe (14Stott K. Keeler J. Van Q.N. Shaka A.J. J. Magn. Reson. 1997; 125: 302-324Crossref Scopus (407) Google Scholar) experiments as shown in Fig.6 B. Selective inversion of the resonance at δ 6.93 resulted in a positive enhancement of the signals at δ 8.09 and δ 4.76, thus proving that the major product isomer had the configuration as shown in Structure 3a.Figure 6One-dimensional-TOCSY (A) of selective perturbation of the signals at δ 2.75 and one-dimensional proton nOe difference spectra irradiating signal at δ 6.93 (B) compared with the mixture 1H spectrum (C) at 600 MHz.View Large Image Figure ViewerDownload Hi-res image Download (PPT) The other new components observed in the spectra were characterized in the same way. The precursor to Structures 3a and 3b was Structure FT4 and was steadily converted to the olefins (Structure FT3) on standing. Structure 4's molecular mass was 360 Da. The spectrum in Fig. 3 C was not definitive, because there are three chiral centers, and the eight diastereoisomers are paired into four NMR distinguishable structures. The spectrum obtained by HPLC-NMR established the presence of two NMR-distinguishable structures. The multiplets at δ 4.84 and δ 4.91 and their coupled partners from the one-dimensional TOCSY at δ 2.11, ∼δ 2.3 (obscured by methyls), and δ 7.99 suggested the presence of two of the diastereomeric structures represented by Structure FT4. We have found no evidence of the formation of the remaining two possible diastereoisomers, possibly because these are also transient products present at even lower concentrations than their isomers. From the NMR data obtained, we are unable to assign the stereochemistry of the observed diastereoisomers. The third (minor) component consisted of the compounds withm/z of 297. Their identities were more difficult to prove, because they were present at low concentration. However, the HPLC-NMR-MS resolved them satisfactorily and confirmed their structures that of Structure FT5. The key information was the absence of any signal between 4 and 5 ppm and the presence of two mutually coupled pairs of methylene groups. Two isomeric forms of this compound were observed, the E andZ forms. However, owing to the small quantity (∼2 μg) present in the mixture, it was not feasible to prove which was the major isomer. The observed chemical shifts and coupling constants for the various components identified in the mixture at 310 K after 12 days of reaction are listed in Table I.Table IAnalysis data of reactants and productsKey to abbreviations: b, broad; c, complex; d, doublet; m, multiplet; nd, not detected; o, obscured; q, quartet; s, singlet; t, triplet. Open table in a new tab Key to abbreviations: b, broad; c, complex; d, doublet; m, multiplet; nd, not detected; o, obscured; q, quartet; s, singlet; t, triplet. Concentrations of compounds in the reaction mixture after 36 h of incubation were PP 6.9 mm, P5C 4.6 mm, and the three products 1.14 mm (Structure 3a), 0.23 mm(Structure 3b), and 1.50 mm (Structure FT4). To discover whether the same reactions occur at lower concentrations (closer to those expected in vivo), aliquots of each stock solution were diluted 10-fold with D2O, mixed, and again incubated at 310 K. This reaction was monitored by 1H NMR and MS and confirmed that products were formed with similar chemical shifts in the1H NMR and quasimolecular ions of the same mass as those observed in the reaction at the higher concentration. We incubated P5C with a range of aldehydes and ketones and successfully formed condensation products with formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, valeraldehyde, benzaldehyde, pyruvic aldehyde, glyoxylic acid, pyruvic acid (methyl glyoxylic acid), acetoacetic acid, 2-oxobutyric acid, and oxaloacetic acid. New products were confirmed by gas chromatography-MS (GC-MS) of their trimethylsilyl (tms) derivatives. The first seven of these (all aldehydes) had products with the molecular mass predicted for di-tms derivatives. The second group of four acids had tri-tms, and the last, oxaloacetic acid, had a tetra-tms derivative of the corresponding P5C/carbonyl adduct (comparable with Structure FT4 for P5C/PP). The key product was the acetoacetic acid/P5C adduct, molecular mass 432 Da, for the tri-tms derivative. We found the latter in the first urine sample collected from the child at the time of her acute illness. This specimen showed moderate ketonuria (4 mm) upon stick testing. The characterization of this adduct and others, will be the subject of a separate publication. Vita" @default.
• W2140333559 created "2016-06-24" @default.
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• W2140333559 date "2001-01-01" @default.
• W2140333559 modified "2023-10-16" @default.
• W2140333559 title "Pyridoxal Phosphate De-activation by Pyrroline-5-carboxylic Acid" @default.
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