New Families of Enantiopure Cyclohexenone cis-Diol, o-Quinol Dimer and Hydrate Metabolites from Dioxygenase-catalysed Dihydroxylation of Phenols

SUPPORTING INFORMATION

New Families of Enantiopure Cyclohexenone cis-Diol, o-Quinol Dimer and Hydrate Metabolites from Dioxygenase-catalysed Dihydroxylation of Phenols

Derek R. Boyd,^a* Narain D. Sharma,^a John F. Malone ^a and Christopher C. R. Allen ^b

^a School of Chemistry and Chemical Engineering

^b School of Biological Sciences

Queens University of Belfast, Belfast, BT9 5AG, UK

General Procedure

H and ¹³C NMR spectra were recorded on Bruker Avance DPX-300 and DPX-500 instruments. Chemical shifts ( ) are reported in ppm relative to SiMe₄ and coupling constants (J) are given in Hz. Mass spectra were run at 70 eV, on a VG Autospec Mass Spectrometer, using a heated inlet system. Accurate molecular weights were determined by the peak matching method, with perfluorokerosene as the standard. CD spectra were recorded in spectroscopic grade acetonitrile using a JASCO J-720 instrument. A PerkinElmer 341 polarimeter was used for optical rotation ([ ]_D) measurements (ca. 20 sC, 10^-1 deg cm² g^-1). Flash column chromatography and preparative layer chromatography (PLC) were performed on Merck Kieselgel type 60 (250 - 400 mesh) and PF_254/366 respectively. Merck Kieselgel type 60F₂₅₄ analytical plates were employed for TLC. Phenol substrates 1b, 1c, 1d, and 1f, 3-methylcatechol 2c and (-)-(S)-camphanic chloride were purchased from Aldrich and used as received.

Small scale (0.2-4.00 g) shake flask biotransformations, with the whole cells of P. putida UV4 (TDO), were performed using methods described earlier^1,2 for non-phenolic aromatic substrates. The biotransformation conditions were not optimised for the phenol substrates used in this study. The aq. culture medium, obtained after the biotransformation, was concentrated under reduced pressure at ca. 40 sC, the concentrate repeatedly extracted (EtOAc), and the extract concentrated under reduced pressure to give the crude mixture of bioproducts. ¹H NMR spectra of the bioproduct mixtures were routinely recorded, before further purification. The bioproducts were separated either by flash column chromatography and/or PLC. Catechols 2d and 2f isolated during the study showed identical physical and spectral characteristics to those reported.^3-5 The enantiomeric excess (ee) values of metabolites 1f_S, 6b_R 6c_S and 6d_R, were indirectly estimated from NMR spectroscopic analysis of their boronate derivatives. The required (-)-(S)- and (+)-(R)-2-(1-methoxyethyl)benzene boronic acids were synthesised and used according to the literature method.^6,7

Biotransformations of phenols and other substrates using P. putida UV4

(i) Substrate 2,5-dimethylphenol (p-xylenol) 1d

The crude mixture of bioproducts (2.3 g) from substrate 1d (1.2 g), on separation / purification by PLC (EtOAc/hexane, 3:2, two elutions), gave three compounds. These were identified as cyclohexenone cis-diol 6d_R, o-quinol dimer 11d and catechol 2d.

(4S,5R,6S)-4,5-Dihydroxy-3,6-dimethylcyclohex-2-enone 6d_R

Enone cis-diol 6d_R was obtained as a white crystalline solid (0.256 g, 17%), m.p. 134-36 sC (EtOAc/hexane); R_f (0.29, EtOAc/hexane, 3:1); ee ≥ 98%; [ ]_D + 94 (c 1.05, in MeOH); HRMS (EI): Found 156.0785. requires C₈H₁₂O₃156.0786; ¹H-NMR (500 MHz, CDCl₃) 5.94 (1H, dq, J = 3.1, 1.3 Hz, 2-H), 4.45 (1H, m, J = 3.1, 3.5, 9.3 Hz, 4-H), 4.25 (1H, m, J = 3.5, 2.4 Hz, 5-H), 2.71 (1H, d, J = 9.3 Hz, OH), 2.57 (1H, dq, J = 2.4, 7.0 Hz, 6-H), 2.26 (1H, d, J = 4.8 Hz, OH), 2.05 (3H, d, J = 1.3 Hz, Me), 1.26 (3H, d, J = 7.0 Hz, Me); ¹³C NMR (125 MH_Z, CDCl₃) 199.1, 159.0, 127.2, 76.3, 72.2, 47.0, 20.5, 11.7; IR(KBr) _max/cm^-1 1646 ( unsaturated ketone); CD λ 209 nm (Δε -13.23), λ 237 nm (Δε +10.00).

(1R,2S,3R,7S,8S,10R)-3,10-Dihydroxy-3,6,10,12-tetramethyltricyclo[6.2.2.0^2,7]-dodeca-

5,11-diene-4,9-dione 11d

Bis-ketol 11d was obtained as colourless plates (0.092 g, 7%), m.p. 202-04 sC (MeOH) lit.⁸ m.p. 190-91 sC); R_f (0.25, EtOAc/hexane, 1:1); ee ≥ 98%; [ ]_D +62.0 (c 0.58, in CHCl₃) (lit⁸ [ ]_D +45.7); HRMS (EI): Found 276.1363. requires C₁₆H₂₀O₄ 276.1361; ¹H-NMR (500 MH_Z, CDCl₃) 6.02 (1H, br s, 5-H), 5.80 (1H, dq, J = 3.4, 1.6 Hz, 11-H), 4.0 (1H, br s, OH), 3.32 (1H, m, J = 3.4, 6.6 Hz, 7-H), 3.15 (3H, m, 1-H, 2-H and 8-H), 2.24 (1H, br s, -OH), 2.02 (3H, d, J = 1.2 Hz, Me), 1.60 (3H, d, J = 1.6, Me), 1.30 (3H, s, Me), 1.25 (3H, s, Me); ¹³C NMR (125 MH_Z, CDCl₃) Compound 11d showed identical physical and spectroscopic characteristics to those reported.⁸

3,6-Dimethyl-2,3-dihydroxybenzene 2d

Catechol 2d was isolated as a white crystalline solid (0.0125 g, 9%), m.p.101-102 sC; R_f (0.55, EtOAc/hexane, 2:3). It showed identical physical and spectroscopic characteristics to those reported.^3,4

(ii) Substrate 3-methylphenol (m-cresol) 1c

An ethyl acetate solution of the crude mixture of bioproducts , obtained from substrate 1c (0.75 g), was purified through a silica gel column. The ethyl acetate fraction collected was concentrated. The residue, on the purification by PLC (EtOAc), gave two compounds which were identified as cyclohexenone cis-diol 6c_S and 3-methylcatechol 2c (0.034 g, 4%).

(4R,5S)-4,5-Dihydroxy-3-methylcyclohex-2-enone 6c_S

Colourless crystalline solid (0.146 g, 15%), m.p. 80-81 sC (EtOAc/Et₂O); R_f (0.35, EtOAc); ee ≥ 98%; [ ]_D -115 (c 1.00, in MeOH); HRMS (EI): Found 142.0632. requires C₇H₁₀O₃ 142.0630; ¹H-NMR (500 MH_Z, CDCl₃) 5.93 (1H, s, 2-H), 4.33 (1H, m, 4-H), 4.28 (1H, ddd, J = 6.7, 4.6, 3.6 Hz, 5-H), 3.37 (2H, m, 2 x OH), 2.74 (1H, dd, J = 6.7, 16.3 Hz, 6-H), 2.57 (1H, dd, J = 4.6, 16.3 Hz, 6-H) 2.09 (3H, s, Me) ¹³C NMR (125 MH_Z, CDCl₃) 195.2, 157.6, 125.2, 68.3, 67.1, 40.5, 19.2; IR(KBr) _max/cm^-1 1637 ( unsaturated ketone); CD λ 209 nm (Δε +5.82), λ 237 nm (Δε -8.73).

(iii) Substrate 2-methylphenol (o-cresol) 1b

The crude mixture of bioproducts obtained from substrate 1b (2 x 1.5 g) was subjected to flash column chromatography with increasing percentage of EtOAc in hexane. The fractions collected with EtOAc/hexane (2:1) were pooled together, evaporated, and the residue purified by PLC ( EtOAc/hexane, 3:1) to give cyclohexenone cis-diol 6b_R

(4S,5R,6S)-4,5-Dihydroxy-6-methylcyclohex-2-enone 6b_R

Colourless crystalline solid (0.041g, 1%), m.p. 128-30 sC (EtOAc/hexane); R_f (0.32, EtOAc/hexane, 3:1); ee ≥ 98%; [ ]_D +223 (c 0.48, in MeOH); HRMS (EI): Found 142.0624. requires C₇H₁₀O₃ 142.0630; ¹H-NMR (500 MH_Z, CDCl₃) 6.66 (1H, ddd, J = 10.3, 4.5, 2.5 Hz, 3-H), 6.05 (1H, dd, J = 10.3, 2.5 Hz, 2-H), 4.6 (1H, m, J = 4.5, 2.5 Hz, 4-H), 4.27 (1H, m, J = 4.5, 2.2 Hz, 5-H), 2.83 (1H, br s, OH), 2.58 (1H, dq, J = 2.2, 6.9 Hz, 6-H), 2.37 (1H, br s, OH), 1.27 (3H, d, J = 6.9 Hz, Me); ¹³C NMR (75 MH_Z, CDCl₃) 202.7, 151.4, 130.2, 77.6, 71.5, 48.0, 12.3; IR(KBr) _max/cm^-1 1668 ( unsaturated ketone); CD λ 200 nm (Δε -18.05), λ 232 nm (Δε +16.10).

(iv) Substrate 3-iodophenol 1f

The crude mixture of bioproducts from substrate 1f (0.8 g), on purification by PLC (EtOAc/hexane, 1:1, two elutions), gave three compounds. These were identified as cyclohexenone cis-diol 6f_S, ketol 13 and 3-iodocatechol 2f ⁵ (0.067 g, 8%).

(4S,5S)-4,5-Dihydroxy-3-iodocyclohex-2-enone 6f_S

Colourless crystalline solid (0.390g, 42%), m.p. 98-100 sC (Me₂CO); R_f (0.21, EtOAc/hexane, 1:1); ee ≥ 98%; [ ]_D -38 (c 0.91, in MeOH); HRMS (EI): Found 253.9468. requires C₆H₇IO₃ 253.9440; ¹H-NMR (300 MH_Z, CDCl₃ + D₂O) 6.91 (1H, d, J = 1.3 Hz, 2-H), 4.52 (1H, dd, J = 1.3, 3.5 Hz, 4-H), 4.41 (1H, ddd, J = 3.5, 3.5, 5.9 Hz, 5-H), 2.82 (1H, dd, J = 5.9, 16.7 Hz, 6-H), 2.65 (1H, dd, J = 3.5, 16.7 Hz, 6-H); ¹³C NMR (125 MH_Z, CDCl₃) 192.4, 141.0, 130.0, 73.5, 67.8, 42.4; IR(KBr) _max/cm^-11644 ( unsaturated ketone).

(R)-4-Hydroxycyclohex-2-enone 13

Light yellow oil (0.027g, 7%); R_f (0.48, EtOAc); [ ]_D +106.0 (c 1.25,in CHCl₃) (lit.^9,10 [ ]_D +110); ¹H NMR (500 MH_Z, CDCl₃) 6.96 (1H, ddd, J = 10.3, 1.8, 3.6 Hz, 3-H), 5.97 (1H, d, J = 10.3 Hz, 2-H), 4.59 (1H, m, 4-H), 2.51-2.64 (1H, m, HCH), 2.32-2.41 (2H, m, H₂C),1.81-2.08 (1H, m, HCH). The physical and spectroscopic data of hydroxycyclohexenone 13 were identical with those reported.^9,10

(v) Substrate (4R,5S)-4,5-dihydroxycyclohex-2-enone 6a_S

The crude mixture of metabolites from substrate 6a_S (0.060g) was purified by flash column chromatography with an increasing percentage of EtOAc in hexane. The fractions collected with EtOAc/hexane (1:1), on evaporation, yielded (R)-4-hydroxycyclohex-2-enone 13 (0.012g, 23%), [ ]_D +104.0 (c 0.5, in CHCl₃). The column was finally eluted with EtOAc/MeOH (9:1). The fraction was evaporated and the residual light yellow semi-solid crystallized to give cyclohexane-1,2,4-triol 14.

(1R,2S,4S)-Cyclohexane-1,2,4-triol 14

Light yellow transparent crystalline solid (0.026g, 42%), m.p. 137-38 sC (EtOAc/EtOH); (lit.¹² m.p. 137-38 sC); R_f (0.24, CHCl₃/MeOH, 7:1); [ ]_D +17 (c 0.55, in EtOH); HRMS (EI): Found 132.0782. requires C₆H₁₂O₃ 132.0786; ¹H-NMR (500 MH_Z, CD₃OD) 3.79 (1H, m, 1-H), 3.66-3.60 (2H, m, 2-H and 4-H), 191-1.85 (2H, m, H₂C), 1.78-1.72 (1H, m, HCH), 1.64-1.60 (2H, m, H₂C), 1.49-1.42 (1H, m, HCH); ¹³C NMR (125 MH_Z, CD₃OD) 71.9, 70.1, 69.5, 38.6, 30.1, 28.4. The physical and spectroscopic data of triol 14 were found to be identical with those reported.^11,12

Monocamphanate ester 7d

A stirred solution of ketodiol 6d_R (0.030g, 0.19 mmol ) in dry pyridine (0.4 mL) was treated with (-)-(S)-camphanic chloride (0.05g, 0.23 mmol) at room temperature. After stirring the reaction mixture for 3 h at room temperature, the pyridine was distilled off under reduced pressure. The residue was extracted with EtOAc (20 mL), the extract washed with aq. 5% NaHCO₃ solution (15 mL) and then with water. The extract was dried (Na₂SO₄) and the solvent evaporated under reduced pressure. The crude product, on purification by PLC (EtOAc/hexane, 1:1), separated into two compounds: the more polar ester, monocamphanate 7d (35%) formed at the 5-hydroxyl, and the less polar diastereoisomer (65%) at the 4-hydroxy positions. Monocamphanate 7d was obtained as white crystalline solid (0.014g, 30%); m.p. 156-58 sC (Et₂O); R_f (0.28, EtOAc/hexane, 1:1); [ ]_D +39 (c 0.51, in CHCl₃); HRMS (EI): Found 336.1554. requires C₁₈H₂₄O₆ 336.1573; ¹H-NMR (500 MH_Z, CDCl₃) 5.97 (1H, br s, 2-H), 5.74 (1H, dd, J = 2.6, 2.6 Hz 5-H), 4.76 (1H, br s, 4-H), 2.75 (1H, dq, J = 2.6, 7.0 Hz, 6-H), 2.34 (1H, br s, OH), 2.31 (1H, m, camphanic H), 2.03 (1H, m, camphanic H), 2.03 (3H, d, J = 1.3 Hz, CH₃), 1.89 (1H, m, camphanic H), 1.67 (1H, m, camphanic H), 1.20 (3H, d, J = 7.0 Hz, Me), 1.10 (3H, s, Me), 0.97 (3H, s, Me), 0.95 (3H, s, Me);¹³C NMR (125 MH_Z, CDCl₃)

Monocamphanate ester 12d

o-Quinol dimer 11d (0.015g, 0.054 mmol) was reacted with (-)-(S)-camphanic chloride (0.015g, .069 mmol) as described in the preceding experiment. The crude product, on purification by PLC (EtOAc/hexane, 2:3), gave monocamphanate ester 12d as colourless crystals (0.019g, 77%); m.p. 126-28 sC (EtOAc/hexane); R_f (0.35, EtOAc/hexane, 2:3); [ ]_D -2.2 (c 0.43, in CHCl₃); HRMS (EI): Found 456.2149. requires C₂₆H₃₂O₇ 456.2148; ¹H-NMR (500 MH_Z, CDCl₃) 6.03 (1H, dq, J = 2.3, 1.2 Hz, 5-H), 5.80 (1H, dq, J = 2.2, 1.6 Hz, 11-H), 4.03 (1H, s, OH), 3.86 (1H, dd, J = 2.2, 8.0 Hz, 7-H), 3.47 (1H, dd, J = 2.1, 8.0 Hz, 8-H), 3.29 (1H, dd, J = 2.1, 8.0 Hz, 1-H), 2.59 (1H, dd, J = 2.1, 8.0 Hz, 2-H), 2.47 (1H, m, camphanic H), 2.04 (1H, m, camphanic H), 2.02 (3H, d, J = 1.2 Hz, Me), 1.93 (1H, m, camphanic H), 1.69 (1H, m, camphanic H), 1.63 (3H, d, J = 1.6 Hz, Me), 1.51 (3H, s, Me), 1.27 (3H, s, Me), 1.13 (3H, s, Me), 1.06 (3H, s, Me), 1.03 (3H, s, Me).

Substitution reactions of (4S,5S)-4,5-dihydroxy-3-iodocyclohex-2-enone 6f_S

(4S,5R)-4,5-Dihydroxy-3-cyanocyclohex-2-enone 6g_S

To a solution of enone cis-diol 6f_S (0.100g, 0.39 mmol) in anhydrous THF (10 mL) were added

Bu₃SnCN (0.186g, 0.59 mmol), Pd(Ph₃P)₄ (0.050g) and Et₃N (125L). The reaction mixture was refluxed until the starting material had been consumed (ca. 18h). The cooled reaction mixture was loaded onto a column of silica gel and eluted with hexane containing an increasing percentage of EtOAc. The fractions collected with EtOAc/hexane (1:1) were evaporated and the residue purified by PLC (MeOH/CHCl₃, 1:19) to give cyclohexenone cis-diol 6g_S as a light yellow oil (0.029g, 48%); R_f (0.31, MeOH/CHCl₃, 1:19); [ ]_D=-136 (c 0.85,in MeOH); HRMS (EI): Found 153.0433. requires C₇H₇O₃N 153.0426; ¹H-NMR (500 MH_Z, CD₃OD) 6.44 (1H, d, J = 2.0 Hz, 2-H), 4.48 (1H, dd, J = 2.0, 3.6 Hz, 4-H), 4.18 (1H, ddd, J = 5.0, 7.0, 3.6 Hz, 5-H), 2.61 (2H, m, J = 7.0 Hz, 6-H and 6-H); ¹³C NMR (125 MHz, CD₃OD)

(4S,5R)-4,5-Dihydroxy-3-carbomethoxycyclohex-2-enone 6h_S

To a solution of cyclohexenone cis-diol 6f_S (0.070g, 0.28 mmol) in MeOH (6 mL) were added Pd(OAc)₂ (0.013g) and NaOAc.3H₂O (0.076g). The mixture was stirred, at rt under an atmosphere of carbon monoxide, until the reaction was complete (ca. 12h). The reaction mixture was filtered, the filtrate concentrated, and the crude product purified by PLC (EtOAc/hexane, 3:1). Enone cis-diol 6h_S was obtained as a colourless oil (0.034 g, 66%); R_f (0.35, EtOAc/hexane, 3:1); [ ]_D -48 (c 1.34, in MeOH); HRMS (EI): Found 186.0528. requires C₈H₁₀O₅ 186.0522; ¹H-NMR (500 MHz, CDCl₃) 6.68 (1H, s, 2-H), 4.73 (1H, d, J = 3.5 Hz, 4-H), 4.20 (1H, ddd, J = 8.5, 3.6, 3.6 Hz, 5-H), 3.82 (3H, s, CO₂Me), 2.79 (1H, dd, J = 8.5, 16.5 Hz, 6-H), 2.57 (1H, dd, J = 3.6, 16.5 Hz, 6-H); ¹³C NMR (125 MHz, CDCl₃)

(4R,5S)-4,5-Dihydroxycyclohex-2-enone 6a_S

A solution of cyclohexenone cis-diol 6f_S (0.100g, 0.39 mmol) in MeOH (7.5 mL), containing Et₃N (65 L) and 3% Pd/C (0.015g), was stirred, overnight at room temperature, in an atmosphere of hydrogen. The catalyst was filtered off, the filtrate concentrated and the crude product purified by PLC (EtOAc/hexane, 3:1, two elutions). Enone cis-diol 6a_S was obtained as a white crystalline solid (0.041g, 81%); m.p. 72-74 sC; R_f (0.28, EtOAc); [ ]_D -217 (c 0.92, in MeOH); HRMS (EI): Found 128.0480. requires C₆H₈O₃; 128.0473; ¹H-NMR (500 MH_Z, CD₃OD₃) 6.73 (1H, m, J = 10.3, 2.9 Hz, 3-H), 5.88 (1H, dd, J = 10.3, 2.1 Hz, 2-H), 4.41 (1H, dd, J = 2.9, 5.3 Hz, 4-H), 4.13 (1H, ddd, J = 5.3, 6.9, 3.7 Hz, 5-H), 2.55 (2H, m, J = 3.7, 5.3 Hz, 6-H and 6-H); ¹³C NMR (125 MH_Z, CDCl₃) 200.4, 152, 130.7, 71.63, 69.0, 45.2; CD λ 205 nm (Δε +11.80), λ 232 nm (Δε -14.31).

The physical and spectroscopic data of enone cis-diol 6a_S were identical with those reported for the opposite enantiomer.¹³

References

D. R. Boyd, N. D. Sharma, S. A. Haughey, M. A. Kennedy, B. T. McMurray, G. N. Sheldrake, C. C. R. Allen, H. Dalton, K. Sproule, J. Chem. Soc. Perkin Trans.

D. R. Boyd, N. D. Sharma, L. V. Modyanova, J. G. Carroll, J. F. Malone, C. C. R. Allen, J. T. G. Hamilton, D. T. Gibson, R. E. Parales, H. Dalton, Can. J. Chem., 2002, 80, 589.

A. Pezzella, L. Lista, A. Napolitano.M. dIschia,Tetrahedron Lett., 2005, 46, 3541.

M. W. Baines, D. B. Cobb, R. J. Eden, R. Fielden, J. N. Gardener, A. M. Roe, W. Tertiuk, G. L. Willey, J. Med. Chem., 1965, 8, 81.

K. Venkatesan, P. H. J. Kouwer, S. Yagi, P. Muller, T. M. Swager, J. Mater. Chem., 2008, 18, 400.

K. Burgess, A. M. Porte, Agnew. Chem. Int. Ed. Engl.,

S. M. Resnick, D. S. Torok, D. T. Gibson, J. Org. Chem

S. Dong, J. Zhu, J. A. Porco, J. Am. Chem. Soc., 2008, 130, 2739.

J. E. Audia, L. Boisvert, A. D. Patten, A. Villalobos, S. J. Danishefsky, J. Org. Chem.,

A. S. Demir, O. Sesenoglu, Org. Lett., 2002, 4, 202.

G. E. McCasland, M. O. Naumann, L. J. Durham, J. Org. Chem

C. Colas, B. Quiclet-Sire, J. Cleophax, J. M. Delaumeny, A. M. Sepulchre, S. D. Gero, J. Am. Chem Soc.,

N. Ran, D. R. Knop, K. M. Draths, J. W. Frost, J. Am. Chem Soc., 2001, 123, 10927.