A New Model for Asymmetric Amplification in Amino Acid Catalysis - Supporting information Martin Klussmann, Hiroshi Iwamura, Suju P. Mathew, David H. Wells, Urvish Pandya, Alan Armstrong and Donna G. Blackmond Department of Chemistry and Department of Chemical Engineering and Chemical Technology, Imperial College, London SW7 2AZ, United Kingdom D.BLACKMND@IMPERIAL.AC.UK Supplementary Methods Materials Samples of scalemic proline were prepared by mixing enantiopure L- and D-proline (unless noted otherwise) and grinding them in a mortar, these were then stored in a desiccator. Samples of other scalemic amino acids were prepared by mixing racemic DL- and enantiopure L-amino acids and used directly. DMS and DMF were purchased as anhydrous from Aldrich, all other chemicals were obtained from commercial sources and used as received. HPLC analysis The column used was a Macherey-Nagel Nucleosil Chiral 1 column, eluent was an aqueous solution of 0.25mM CuS 4 and 0.025mM H 2 S 4 with 0-35% Methanol, flow rate 0.3-1.5ml/min, temperature 50 C, UV-VIS Detector at 250nm. For alanine, leucine, methionine, phenylalanine, proline and valine, the L-enantiomer was eluting first, whereas for histidine and serine it was the D-enantiomer. ptimum sample concentration was 1-2 mg/ml. Solid samples were dissolved in water, solution samples from water or DMS were filtered with a PTFE syringe filter and diluted with water accordingly. For concentration measurement, aqueous stock solutions of known concentrations (ca. 4mg/ml) of L-phenylalanine, D-serine or L-leucine were used as standards. These were added to a known quantity of a filtered solution of the amino acid, eventually diluted to an adequate concentration. The amino acid concentration was then calculated from the peak ratio in the chromatogram using a previously determined response factor. From this and the ee values, the ee of leftover solid could be calculated. To control the accuracy of the analysis, the ee of the solid phase was at times measured and compared with the calculated values. Generally, a good agreement was achieved.
Concentration and ee of proline in DMS Proline samples were stirred in dry or aqueous DMS at 25 C for at least 24 hours until equilibrium was reached and concentration and ee values were stable. In all cases, an excess of undissolved proline was present. Entries 1-9 in Supplementary Table 1 were taken to construct Figure 1b, entries 10-31 were used to construct the ternary phase diagram (Figure 2). Supplementary Table 1: Equilibrium concentrations and ee of saturated proline solutions. # %ee empl [Pro] solvent [Pro] solution %ee solution %ee solid %ee solid calc 1 0.0 0.10 aq. DMS a 0.0221 0.2 1.4-0.1 2 5.0 0.10 aq. DMS a 0.0244 26.3 1.7-1.9 3 10.0 0.10 aq. DMS a 0.0261 41.1 1.7-0.9 4 20.0 0.10 aq. DMS a 0.0286 53.4 11.7 6.6 5 40.0 0.10 aq. DMS a 0.0296 52.4 41.9 34.8 6 60.0 0.10 aq. DMS a 0.0292 48.0 68.8 64.9 7 80.0 0.10 aq. DMS a 0.0305 49.8 94.2 93.6 8 90.0 0.10 aq. DMS a 0.0268 62.5 99.6 100.3 9 100.0 0.10 aq. DMS a 0.0192 100.0 n.d. 100.0 10 0.0 0.10 dry DMS 0.0195-0.9 0.9-0.1 11 5.0 0.10 dry DMS 0.0209 27.9 1.1-1.0 12 10.0 0.10 dry DMS 0.0229 40.4 1.8 0.9 13 20.0 0.10 dry DMS 0.0245 51.6 13.5 9.8 14 40.0 0.10 dry DMS 0.0248 47.8 40.2 37.4 15 60.0 0.10 dry DMS 0.0248 47.0 68.4 64.3 16 80.0 0.10 dry DMS 0.0270 49.2 92.9 91.4 17 90.0 0.10 dry DMS 0.0238 56.1 99.7 100.2 18 100.0 0.10 dry DMS 0.0167 100.0 n.d. 100.0 19 0.0 0.35 dry DMS 0.0186-0.3-0.4 0.0 20 5.0 0.35 dry DMS 0.0249 50.7 3.6 1.6 21 10.0 0.35 dry DMS 0.0246 53.5 6.7 6.7 22 20.0 0.35 dry DMS 0.0239 54.2 21.4 17.6 23 40.0 0.35 dry DMS 0.0240 49.9 41.0 39.3 24 60.0 0.35 dry DMS 0.0242 48.9 62.5 60.8 25 80.0 0.35 dry DMS 0.0252 48.1 n.d. 82.5 26 90.0 0.35 dry DMS 0.0249 47.9 94.0 93.4 27 100.0 0.35 dry DMS 0.0161 100.0 n.d. 100.0 28 10.0 0.03 dry DMS 0.0198 15.4 n.d. -0.3 29 90.0 0.04 dry DMS 0.0185 81.0 n.d. 97.7 30 90.0 0.04 dry DMS 0.0193 80.7 99.6 98.5 31 90.0 0.08 dry DMS 0.0217 64.9 99.8 99.4 [Pro]: total concentration of proline employed; %ee empl : %ee of employed L-proline; [Pro] solution : solution concentration of proline after 24-48 hours; %ee solution : %ee of proline in solution after 24-48 hours; %ee solid : %ee of undissolved solid phase proline after 24-48 hours, measured by HPLC; %ee solid calc : calculated %ee values of undissolved solid phase proline; a : DMS with 0.35M water.
Saturation concentration of proline in DMS 0.034 0.032 0.030 0.028 [proline] 0.026 0.024 0.022 0.020 0.018 0.1M, aqueous DMS 0.1M dry DMS 0.35M dry DMS 0.016 0.014 0 10 20 30 40 50 60 70 80 90 100 employed proline %ee Supplementary Figure 1: Saturation concentrations of proline in dry or aqueous (0.35M water) DMS, taken for samples of varying enantiomeric composition and different total concentrations of proline (Constructed from data in Supplementary Table 1). equilibrium solution %ee of proline in DMS 100 90 80 0.1M aqueous DMS 0.1M dry DMS 0.35M dry DMS solution proline %ee 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100 employed proline %ee Supplementary Figure 2: Equilibrium solution enantiomeric excess of proline in dry or aqueous (0.35M water) DMS, taken for samples of varying enantiomeric composition and different total concentrations of proline (Constructed from data in Supplementary Table 1).
Concentrations and ee of various amino acids in water Scalemic amino acid samples of various ee's were stirred in water at 25 C, using an excess of amino acid so that the solution in equilibrium was saturated in both solids (This was checked by measuring the remaining solid ee). Samples for HPLC were taken as described above at various intervals, at least two days were allowed to reach equilibrium. For leucine, methionine and phenylalanine, D-serine was used as standard for concentration measurement, for all others, L-leucine was used. Values given in the article in Table 1 are average values of at least two samples. FTIR studies of solid proline Proline samples (Lancaster) of various sources or methods of preparations were compared by taking IR spectra in KBr. Unless otherwise noted, proline was used as received. Appearances of characteristic NH- and H-bands are listed. Supplementary Table2: FTIR studies of solid proline. # Sample bands crystal phase assignment 1 L-proline (Lancaster) 3423 cm -1 enantiopure 2 L-proline (0.1M) stirred in DMS for 22hrs, filtered and dried in vacuum at 85 C over night 3 mechanical mixture of D and L- proline 3423 cm -1 enantiopure 3423 cm -1 enantiopure 4 D,L-proline (Lancaster) 3390, 3198 cm -1 racemic compound 5 mechanical mixture of D and L- proline, stirred in DMS for 22hrs, filtered and dried in vacuum at 85 C over night 3390, 3198 cm -1 racemic compound Aldol reactions CH Cl + Amino acid solvent, 25 C H Cl (1) Supplementary Equation 1: Amino acid catalysed aldol reaction of 2-chlorobenzaldehyde and acetone. H Amino acid water, RT H H H + H + H (2) 1 2 (anti, major enantiomer) 3 (syn) 4 Supplementary Equation 2: Amino acid catalysed aldol reaction of propionaldeyhde.
Aldol reaction with proline in DMS According to Supplementary Equation 1, general procedure: To a suspension of proline (scalemic, L or D) in 4.5ml DMS (anhydrous or with ca. 0.8w% H 2 ) was added acetone and the suspension was stirred at an ambient temperature for ca. 30 min. The reaction was initiated by addition of 2-chlorobenzaldehyde (Aldrich) and the resulting mixture was stirred at 25 C until full conversion was achieved as confirmed by HPLC. Unless noted otherwise, total concentrations were 2.5M acetone, 0.5M 2-chlorobenzaldehyde, 0.35M water, 0.1M proline. The reaction was quenched by addition of an excess water, subsequently extracted with ethyl acetate and dried with MgS 4. This solution of crude product was used directly for HPLC analysis of conversion and ee. (Daicel CHIRALPAK AD, 4.6 mm φ X 250 mm, Hexane / EtH = 95 / 5, flow 1ml/min, 210 nm). Analytical data of samples purified by column chromatography were identical with those reported in the literature. 29 Supplementary Table3: Proline-catalysed aldol reaction in DMS. # %ee L-Proline %ee Prod, A %ee Prod, B %ee Prod, C 1-0.44-1.9 0.0 a -1.3 2 9.98 18.3 6.8 12.9 3 20.02 32.6 15.9 22.8 4 39.83 33.9 30.0 32.3 5 59.83 34.8 43.9 35.7 6 80.41 38.8 56.4 50.9 7 100 70.5 69.7 69.7 %ee L-Proline : %ee of employed L-proline; %ee Prod : %ee of aldol product, depending on reaction conditions: A: 0.10M Proline (Figure 2), B: 0.025M Proline (Figure 2), C: 0.10M Proline, dry DMS; a : with DL-proline.
Aldol reaction with other amino acids in DMF According to Supplementary Equation 1 and the procedure described above for proline, except for the following changes: DMF with 0.88w% water was used as a solvent, the catalysts were stirred in the solvent for 12 hours prior to addition of the substrates and the organic phase in the workup was extracted four times with water. Full conversion was usually not achieved even after six days, although the reaction still proceeded. Conversion values given are from HPLC data. Supporting Table 4: Amino acid catalysed aldol reaction in DMF # AA %ee empl [AA] conv t1 conv t2 %ee t1 %ee t2 1 Serine 1.0 4.01 n.d. 33 n.d. 43.9 2 Serine 9.9 0.30 26 35 46.0 43.9 3 Serine 20.1 0.30 30 36 46.3 44.4 4 Serine 39.8 0.30 28 39 46.5 43.9 5 Serine 59.6 0.30 31 40 45.2 44.4 6 Serine 80.0 0.30 30 43 45.8 44.0 7 Serine 100 0.30 35 44 44.5 43.4 8 Leucine 20.0 3.30 9 55 60.9 58.4 9 Leucine 40.0 3.30 14 56 61.8 58.7 10 Leucine 60.0 3.30 17 56 61.2 59.0 11 Leucine 80.0 3.30 15 54 61.6 59.3 12 Leucine 90.0 3.30 18 55 61.4 59.4 13 Leucine 95.0 3.30 13 51 62.1 59.3 14 Leucine 100 3.30 14 53 68.1 65.3 15 Alanine 20.0 1.20 7 28 34.1 30.7 16 Alanine 40.0 1.20 9 29 35.6 33.3 17 Alanine 60.0 1.20 6 28 37.2 34.4 18 Alanine 80.0 1.20 5 28 39.8 36.0 19 Alanine 100 1.20 7 25 62.2 53.8 20 Valine 10.0 1.00 17 57 29.6 30.4 21 Valine 20.1 1.00 17 57 29.0 29.6 22 Valine 40.0 1.01 16 57 29.6 29.5 23 Valine 60.3 0.99 16 57 28.4 29.2 24 Valine 80.1 0.98 17 58 28.8 28.3 25 Valine 100 1.00 12 46 67.1 68.4 26 Threonine 9.9 0.22 28 45-1.5 0.2 27 Threonine 19.9 0.22 31 50-1.1-0.2 28 Threonine 40.0 0.22 26 53 1.4 0.4 29 Threonine 60.4 0.46 22 36-2.4-0.8 30 Threonine 80.9 0.75 25 51-1.8-0.2 31 Threonine 97.0 5.35 17 44 1.9-0.2 32 Threonine 100 0.13 30 36 58.5 58.1 AA: amino acid used as catalyst; %ee empl : %ee of employed L-amino acid; [AA]: concentration of amino acid; conv t : approximate conversion after given time (Ser t1: 4 days, t2: 6 days; Leu t1: 1 day, t2: 4 days; Ala t1: 1 day, t2: 4 days; Val t1: 1 day, t2: 6 days; Thr t1: 2 days, t2: 4 days); %ee t : %ee of aldol product after given time. Data used in Figure 3: t2, except Valine: t1.
Aldol reaction with other amino acids in water According to Supporting Equation 2, general procedure: to a stirred solution of amino acid (stirred for 15hrs in the case of scalemic samples) in water was added propionaldehyde 1 (2.8M). The reaction mixture was stirred at room temperature (ca. 20 o C) for 4 hours and worked up and analysed as previously reported. 30 Supporting Table 5: Amino acid catalysed aldol reaction of eq. (2). # AA %ee empl [AA] %ee anti anti:syn ratio 4:(2+3) 1 Alanine 100 1.0 6.5 1:1.1 8:1 2 Alanine 50 2.0 7.8 1:1.2 31:1 3 Histidine 100 1.0 16.7 1:1.2 55:1 4 Histidine 50 2.0 17.4 1:1.4 104:1 5 Serine 100 2.0 37.5 1:1 36:1 6 Serine 50 2.0 39.7 1:1 7:1 7 Valine 100 1.0 8.2 1:1.3 7:1 8 Valine 50 2.0 3.7 1:1.4 23:1 AA: amino acid used as catalyst; %ee empl : %ee of employed L-amino acid; [AA]: concentration of amino acid; %ee anti : %ee of anti-aldol product 2. References 29. Tang, Z. et al. Novel Small rganic Molecules for a Highly Enantioselective Direct Aldol Reaction. J. Am. Chem. Soc. 125, 5262-5263 (2003). 30. Northrup, A. B. & MacMillan, D. W. C. The First Direct and Enantioselective Cross- Aldol Reaction of Aldehydes. J. Am. Chem. Soc. 124, 6798-6799 (2002)