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Synthesis of Short-Chain Hydroxyaldehydes and Their 2,4

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Synthesis of Short-Chain Hydroxyaldehydes and Their 2,4 Erschienen in: Journal of chromatography A ; 1531 (2018). - S. 143-150 https://dx.doi.org/10.1016/j.chroma.2017.11.046 Synthesis of short-chain hydroxyaldehydes and their 2,4-dinitrophenylhydrazone derivatives, and separation of their isomers by high-performance liquid chromatography a,∗ b a b Jasmin Frey , Fabian Schneider , Bernhard Schink , Thomas Huhn a Department of Biology, University of Konstanz, D-78457 Konstanz, Germany b Department of Chemistry, University of Konstanz, D-78457 Konstanz, Germany a r t i c l e i n f o a b s t r a c t An easy to handle high-performance liquid chromatography (HPLC) method for the separation of struc- tural isomers of short-chain aldehydes as their hydrazones is presented. Some aldehydes were not available as reference compounds, therefore, synthesis routes for these hydroxy-aldehydes and their dini- trophenylhydrazone derivatives are reported. The reported method has a detection limit of 2.4–16.1 ␮g/L for the hydrazones and shows good linearity and reproducibility for various tested aldehydes. Keywords: Synthesis HPLC method Brady’s reagent Aldehyde DNPH derivatives Hydroxy(iso)butyraldehyde separation 1. Introduction acetone degradation by sulfate-reducing bacteria, the determina- tion of 2-hydroxyisobutyraldehyde, 3-hydroxybutyraldehyde and Aldehydes and ketones of low molecular weight are quite acetoacetaldehyde turned out to be essential for the elucidation of volatile and reactive molecules which tend to form oligomers by a proposed biochemical pathway [9,10]. No method for the analyt- spontaneous reactions, i.e. aldol addition/condensation. This ten- ical separation and quantification of these hydroxyaldehydes has dency, together with further degradation by oxidation makes their been described in the literature. The same holds true for their non- quantitative determination in biological samples rather difficult. hydroxylated congeners butyraldehyde and isobutyraldehyde. Classically, aldehydes are identified after transformation to their In the present work, we describe the synthesis and characteriza- hydrazones by derivatization with 2,4-dinitrophenylhydrazine tion of 2-hydroxyisobutyraldehyde, 3-hydroxybutyraldehyde, and (DNPH). These are stable, non-volatile and often crystalline solids acetoacetaldehyde and their DNPH derivatives as authentic sam- with a sharp melting point. Aldehydes and their DNPH derivatives ples for the intended validation of the proposed biodegradation can be determined by gas chromatography [1,2] or by HPLC on stan- pathway of acetone. Furthermore, an easy to handle HPLC-method dard C18-phases, commonly using water (or buffer)/acetonitrile for separation and detection of butyraldehyde, isobutyraldehyde, (MeCN) mixtures as eluent (in some cases with additional 2-hydroxyisobutyraldehyde, 3-hydroxybutyraldehyde, and ace- methanol, isopropanol and/or tetrahydofurane) [3–7]. Unfortu- toacetaldehyde (in the form of its corresponding [1H]-pyrazole) nately, these methods do not allow separation of structural isomers as DNPH derivatives was developed. We demonstrate that this such as butyraldehyde DNPH and isobutyraldehyde DNPH or their method is applicable also to the separation of other hydra- hydroxy analogues [3–7]. In a non-aqueous system, separation of zones (e.g. for formaldehyde, acetaldehyde, acetoin, acetone, butyraldehyde and isobutyraldehyde was achieved with hexane as crotonaldehyde, and other short-chain aldehydes/ketones). In the an eluent, but this protocol is not applicable to biological samples literature, no method is described that allows a separation of with their variable water content [8]. As possible intermediates of short-chain aldehyde isomers (e.g. 3-hydroxybutyraldehyde and 2-hydroxyisobutyraldehyde) as their hydrazones. The method described here provides a solution to this problem. ∗ Corresponding author at: Microbial Ecology, Department of Biology, Postbox 654, University of Konstanz, D-78457 Konstanz, Germany. E-mail address: [email protected] (J. Frey). Konstanzer Online-Publikations-System (KOPS) URL: http://nbn-resolving.de/urn:nbn:de:bsz:352-2-vletqs4ix3hw2 144 Scheme 1. Decomposition of (E)-4-(2-(2,4-dinitrophenyl)hydrazono)butan-2-one (4) to form pyrazole 8. 2. Methods/experimental section MgSO4, and the solvent was evaporated. 1 was obtained as colorless oil (4.29 g, 32.00 mmol, 84%). 1 2.1. Reagents H NMR (400 MHz, Chloroform-d) ␦ 4.57 (dd, J = 6.0, 5.1 Hz, 1H, C(OCH3)2), 4.13 − 3.87 (m, 1H, COH), 3.38 (s, 3H, OCH3), 3.35 (s, 3H, For HPLC and sample preparation, ultrapure water was obtained OCH3), 1.91 − 1.60 (m, 2H, CH2), 1.20 (d, J = 6.3 Hz, 3H, CH3). 13 using a Milli-Q Water System (Millipore). MeCN was HPLC grade C NMR (101 MHz, Chloroform-d) ␦ 104.1 (C(OCH3)2), 64.8 (HiPerSolv CHROMANORM) from VWR Chemicals (Germany). For (COH), 53.9 (OCH3), 53.0 (OCH3), 41.1 (CH2), 23.5 (CH3). the in situ derivatization a mix consisting of 5 mg DNPH and 0.05% conc. H PO (v/v) in 10 mL MeCN was employed. 3 4 2.3.3. All chemicals of analytical grade or better were pur- (E)-1-(2-(2,4-Dinitrophenyl)hydrazono)-2-methylpropan-2-ol chased from Sigma-Aldrich (Germany), DNPH standards were (2) purchased as certified reference materials solution in MeCN 1,1-Dimethoxy-2-methylpropan-2-ol (1.00 g, 7.46 mmol) was from Aldrich (formaldehyde ([order code: CRM47177), acetalde- dissolved in MeCN (200 mL), then H2SO4 (1.0 g, 10.2 mmol) and hyde (CRM47340), acrolein (CRM47342), acetone (CRM47341), water (750 mg, 38.9 mmol) were added and the mixture stirred crotonaldehyde (CRM47175), butyraldehyde (CRM47345) and at rt for 3 h. Na2SO4 (5 g) and (2,4-dinitrophenyl)hydrazine (sta- isobutyraldehyde (CRM47886)). bilized with 50 wt% water, 2.95 g, 7.46 mmol) were added and the mixture was stirred for 3 h, then adjusted to pH 7.0 using solid 2.2. HPLC system KHCO3 and filtered. The filtrate was evaporated, the product was isolated by column chromatography (DCM, then DCM:MeOH 20:1) A Shimadzu Prominence HPLC system equipped with a pho- and recrystallized from ethanol to obtain 2 as red needle-shaped ® todiode array (PDA) detector (SPD-M20A) and a Kinetex PFP crystals (327 mg, 1.22 mmol, 16%). 1 column (5 ␮m, 100 Å, 250 × 4.6 mm; [order code: 00G-4602-E0] H NMR (400 MHz, DMSO-d6) ␦ 11.31 (s, 1H, NH), 8.84 (d, Phenomenex, USA) was used. A binary gradient system was used J = 2.7 Hz, 1H, Har), 8.35 (dd, J = 9.6, 2.7 Hz, 1H, Har), 8.01 (s, 1H, for separation consisting of 50% H2O (MilliQ water) and 50% MeCN N CH), 7.90 (d, J = 9.6 Hz, 1H, Har), 5.15 (s, 1H, OH), 1.33 (s, 6H, (v/v) kept isocratic during the first 19 min of the run, followed by CH3). 13 a rapid increase to 100% MeCN during minutes 19–20 and kept at C NMR (101 MHz, DMSO-d6) ␦ 158.8 (C N), 145.0 (Car), 136.7 100% MeCN for one minute. A reversion during minutes 21–22 back (Car), 129.7 (Car), 129.1 (Car), 122.9 (Car), 116.4 (Car), 69.7 (COH), to initial concentrations of 50/50 (H2O/MeCN) was set before finally 27.4 (CH3). re-equilibrating the column for 8 min. The flow rate was 1 mL per min and the injection volume was 5 ␮L. The temperature was set ◦ 2.3.4. (E)-4-(2-(2,4-Dinitrophenyl)hydrazono)butan-2-ol (3) to 40 C (column oven and flow cell). The wavelength for detection The compound was prepared following the same procedure was 360 nm with 550 nm set as reference wavelength. as for (E)-1-(2-(2,4- dinitrophenyl)hydrazono)-2-methylpropan- 2-ol 2 using 4,4-dimethoxybutan-2-ol (1) (500 mg, 3.73 mmol), 2.3. Synthesis of aldehydes and hydrazones H2SO4 (500 mg, 5.10 mmol), water (350 mg, 19.43 mmol), (2,4- dinitrophenyl)hydrazine (stabilized with 50 wt% water, 1.48 g, 2.3.1. General remarks 3.73 mmol) and anhydrous Na2SO4 (2.5 g). The product was NMR spectra were measured on Bruker Avance 400 and Bruker obtained in form of yellow crystals (220 mg, 0.82 mmol, 22%). 1 Avance DRX 600 spectrometers. Chemical shifts are referenced H NMR (400 MHz, DMSO-d6) ␦ 11.34 (s, 1H, NH), 8.83 (d, with respect to the chemical shift of the residual protons present in J = 2.7 Hz, 1H, Har), 8.32(dd, J = 9.7, 2.7 Hz, 1H, Har), 8.02 (t, J = 5.9 Hz, the deuterated solvents. The following reference values were used: 1H, N CH), 7.85 (d, J = 9.7 Hz, 1H, Har), 4.77 (d, J = 4.7 Hz, 1H, OH), 1 13 CDCl3: ␦ = 7.26 ppm ( H NMR), ␦ = 77.16 ppm ( C NMR); d6-DMSO: 4.03 − 3.79 (m, 1H, HCOH), 2.41 (t, J = 5.9 Hz, 2H, CH2), 1.15 (d, ␦ 1 13 = 2.50 ppm ( H NMR), ␦ = 39.51 ppm ( C NMR); d8-THF: ␦ = 1.73, J = 6.2 Hz, 2H, CH3). 1 13 13 3.58 ppm ( H NMR), ␦ = 25.37, 67.57 ppm ( C NMR). Data were C NMR (101 MHz, DMSO-d6) ␦ 153.6 (N CH), 144.7 (Car), 136.5 processed using the software MestReNova (v. 10.0). The follow- (Car), 129.7 (Car), 128.6 (Car), 123.0 (Car), 116.3 (Car), 64.3 (COH), ing abbreviations were used for NMR data: s: singlet; d: doublet; t: 42.0 (CH2), 23.4 (CH3). triplet; q: quartet; m: multiplet. Structure assignments were done based on 2D-NMR (COSY, HMBC, HSQC) experiments. 2.3.5. (E)-4-(2-(2,4-Dinitrophenyl)hydrazono)butan-2-one (4) 4,4-Dimethoxybutan-2-one (985 mg, 7.46 mmol) was dissolved 2.3.2.
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