Arthrobacter sp. lipase catalyzed kinetic resolution of BINOL: The effect of substrate immobilization

Journal of Molecular Catalysis B: Enzymatic 101 (2014) 35–39

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Arthrobacter sp. lipase catalyzed kinetic resolution of BINOL: The effect of substrate immobilization Pankaj Gupta a,b,∗ , Abdul Rouf b , Bhahwal Ali Shah b , Neha Mahajan a , Asha Chaubey b , Subhash Chandra Taneja b a b

Government Degree College Kathua, University of Jammu, 184104 J&K, India Indian Institute of Integrative Medicine, Canal Road, Jammu 180 001, J&K, India

a r t i c l e

i n f o

Article history: Received 18 November 2013 Received in revised form 13 December 2013 Accepted 21 December 2013 Available online 29 December 2013

a b s t r a c t (S)-1,1 -Binaphthyl-2,2 -diol was prepared in high optical purity (∼98%) via Arthrobacter sp. lipase (MTCC No. 5125) catalyzed kinetic resolution. The immobilization of the substrate on a solid inert support significantly improved the enantioselectivity factor (E) by almost sixfolds, i.e. from ∼27 to >180. The effect of acyl substituents and co-solvents were also studied. © 2013 Elsevier B.V. All rights reserved.

Keywords: (S)-1,1 -Binaphthyl-2,2 -diol Arthrobacter sp. lipase Kinetic resolution Solid support Co-solvent

1. Introduction Optically active atropisomers of 1,1 -binaphthyl-2,2 -diol (BINOL) 1 are versatile templates for a wide range of chiral catalysts and auxiliaries for asymmetric reactions [1]. Besides asymmetric oxidation [2] and reduction reactions, BINOL is widely used as chiral resolving agent [3], and for asymmetric C C bond formation such as ene- [4], Aldol [5], allylation [6], Diels–Alder [7], Friedel–Crafts [8], Baylis–Hillman [9], and enantioselective meso-epoxide ring opening reactions [10]. Various synthetic as well as chemoenzymatic routes to prepare optically pure BINOL have been reported and reviewed [1], even as classical resolution approaches are being used to synthesize these enantiomers on a preparative scale [11]. Lipases/esterases are the most frequently used enzymes in organic synthesis for the kinetic resolution of racemates because of their acceptance of a broad range of substrates [12]. The first useful method based on cholesterol esterase (bovine pancreatic acetone powder) catalyzed enzymatic resolution of BINOL was reported in 1989 by

∗ Corresponding authors at: Indian Institute of Integrative Medicine, Canal Road, Jammu 180 001, J&K, India. Tel.: +91 1921 224051/9419251800; fax: +91 1922 234315. E-mail addresses: [email protected], [email protected] (P. Gupta), [email protected], [email protected] (S.C. Taneja). 1381-1177/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.molcatb.2013.12.014

Kazlauskas [13]. Later on Inagaki et al. used Pseudomonas aeruginosa lipase for the kinetic resolution [14]. In 2003, Hernandez et al. [15] reported the use of lipoprotein lipase enzymes from Pseudomonas sp. and Pseudomonas fluorescens for mono transesterification of BINOL and its 6,6 -dibromo derivative in non-aqueous environment (i Pr2 O/acetone/vinylacetate) to afford (S)-BINOL up to 80% ee. Aoyagi et al. [16] disclosed the effects of reaction temperature and acyl group on the CAL-B catalyzed hydrolysis of BINOL monoacylates to prepare optically enriched BINOL with 91% ee at 80 ◦ C and 43% yield. Recently Itoh et al. [17] reported an efficient linker-oriented design of bisnapthol derivatives for the kinetic resolution of 6,6 dibromo-bisnapthol with excellent enantioselectivity (E > 200). It is apparent that only a few enzymatic methods have been attempted in the past and the lipase/hydrolase catalyzed resolutions generally gave the products with unsatisfactory enatioselectivity. The bulky binaphthyl rings exerting steric hindrance limit the resolution of diacyl derivatives with hydrolases, while monoacylates to some extent provided better results. Despite these limitations, the resolution of BINOL via biocatalytic resolution particularly by lipases/esterases still remains an attractive challenge for the organic chemists due to synthetic and commercial importance of the products. We have been working in the area of kinetic resolution of important drug intermediates and chiral auxiliaries using the repository of indigenous hydrolases and Arthrobacter sp. (MTCC 5125) has proven to be a source of versatile lipase, capable of high enantioselectivity and a broad range of substrate acceptability

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Scheme 1. Reaction conditions: (i) (RCO)2 O, DMAP, pyridine, toluene, DCM; (ii) (CH3 CO)2 O, DMAP, DCM; (iii) ABL, co-solvent, buffer.

especially the secondary alcohols [18]. Consequently, the applicability of Arthrobacter sp. lipase catalyzed kinetic resolution for the preparation of optically active BINOL became a matter of our interest. In the present communication we report the kinetic resolution of (±)-1,1 -binaphthyl-2,2 -diol in high optical purity (∼98%) via Arthrobacter sp. lipase (MTCC No. 5125) catalyzed hydrolysis of its acylates. 2. Results and discussion After the preparation of the racemic BINOL by oxidative coupling of 2-napthol using FeCl3 ·6H2 O [19], various diacylates were prepared for the kinetic resolution using lipases. Expectedly, all the

available lipases including Arthrobacter sp. lipase used in aqueous buffer solutions, failed to effect enantioselective hydrolysis of the diacetate (±)-5. Therefore, to modify the strategy, the procedure reported by Inagaki et al. [14] was employed for the preparation of racemic mono acylates in overall 80–85% yield. During the preliminary screening experiments Arthrobacter sp. (ABL) was able to hydrolyze the monoesters. The biocatalytic reactions of BINOL are represented in Scheme 1. Our initial experiments were designed so as to find the most suitable substrate and experimental conditions for catalyzing the hydrolysis of a monoester. For this purpose, racemic acylates 2, 3 and 4 were subjected to biocatalytic hydrolysis under different experimental conditions. During the screening experiments with

Table 1 The effect of co-solvents on the hydrolysis of (±)-4, (±)-2 and (±)-3 with Arthrobacter sp. lipase. Entry 1 2 3 4 5 6 7 8 9 10 11 12 13

Substrate

Co − solvent

(±)-2 (±)-2 (±)-2 (±)-2 (±)-2 (±)-2 (±)-2 (±)-2 (±)-2 (±)-3 (±)-3 (±)-4 (±)-4

Nil Toluene Tetrahydrofuran DMSO DMF n-BuOH Dioxane ACN Acetone DMSO DMF DMF DMSO

Convn.

Time (h)

5.6 37.2 ND 32.2 21 4.2 ND ND 12.8 15.5 4.4 5.2 13.5

36 36 – 44 36 36 – – 36 24 36 24 24

eep 57 67.7 – 89.4 85.7 71.4 – – 75 72 40.9 69.2 64

E 3.8 7.5 – 27.6 16.3 6.25 – – 7.8 7.02 2.5 5.7 5.1

All the reactions were carried out in a shaker at 250 rpm. Conversion and ee were determined by chiral HPLC; E (enantiomeric ratio) was determined by using formula E = [ln(1 − convn(1 + eep )]/[ln(1 − convn(1 − eep )] [25], Conc. 20 g/L; ND, not detected. Values in bold indicate the best results. Table 2 Effect of solid support on enzyme catalyzed hydroysis of (±)-4, (±)-2, and (±)-3 using 20% DMSO as a co-solvent. Support

Substrate

Time

Convn.

eep

ees

Nil Silica

(±)-2 (±)-2

44 16

32.2 34.6

89.4 78.6

31.1 42.8

E 27.6 12.5

Celite

(±)-2 (±)-2 (±)-3 (±)-4

24 36 36 24

37.6 46.7 16.9 6.7

98.0 92.7 72.8 91

60.4 81.5 14.8 6.5

181.7 61.1 7.3 22.8

Neu. Alumina Basic Alumina

(±)-2 (±)-2

36 24

43.9 45

64.1 67.5

52.2 55.2

7.4 8.8

P. Gupta et al. / Journal of Molecular Catalysis B: Enzymatic 101 (2014) 35–39

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Fig. 1. HPLC graphs of racemic as well as resolved products.

ABL, it was observed that the rate of hydrolysis was very slow and the enantioselectivity was also poor in aqueous buffer alone. In lipase catalyzed hydrolysis of acylates, biphasic reaction medium has been found to provide fast conversion and improved enantioselectivity [20]. Therefore, to improve the productivity as well as enantioselectivity, the use of co-solvents was envisaged as a practical option. Both non-polar as well as polar solvents in the ratio 1:9 (10%, v/v) in buffer were used (Table 1). Finally DMSO, which is also reported to enhance enantioselectivity of lipase catalyzed hydrolysis [21], was selected to be a co-solvent of choice in terms of rate of hydrolysis as well as enantioselectivity. Further, to achieve higher enantioselectivity, the effect of pH (4–8) was also studied and it was found that pH 7.0 was the most suitable both in terms of rate of hydrolysis as well as enantioselectivity. It could be seen that enantioselectivity of monoacylated BINOL in the presence of ABL was affected by the size of the acyl group. The acetate displayed the best enantioselectivity, while the higher homologues were comparatively slow to react and poor in optical purity (Table 1). One of the main challenges encountered during past attempts by several groups with lipase/esterase catalyzed kinetic resolution of BINOL has been the low optical purities of the products when a direct approach of hydrolysis of the alkylacyl esters was used. Many permutation combinations including variations in the size of the acylate, temperature, solvent and types of biocatalysts have been attempted; however most of these attempts did not produce satisfactory results. Our initial attempts of kinetic resolution with ABL also resulted in maximum ∼89% ee at ∼32% conversion (Table 1, Entry 4). Therefore, we envisaged a distinctive approach, as reported by Grognux et al. [22] and recently reviewed by Flitsch and co-workers [23], to further improve the enantiomeric excess as well as the rate of hydrolysis through immobilization of substrate on an inert solid support. Surprisingly, there are no reports in the literature regarding the immobilization of the substrate or its adsorption on an inert support for the improvements of enantioselectivity as well as rate of the reaction. For the present studies, various inert supports such as silica gel, celite or neutral and basic alumina of various particle sizes were selected. Gratifyingly, adsorption of the substrate over celite support [1:5; substrate: support (w/w), mesh size ≤113 ␮m] led to a significant enhancement of the rate of hydrolysis as well as enantioselectivity. Thus at the same concentration of the substrate, the time taken for 30% conversion (hydrolysis of

Effect of co-solvent concentration on ee 100 95

eep (%) 90 eep(%) 85 80 75 0

5

10

15

20

25

30

DMSO (%) Fig. 2. Effect of co-solvent concentration on ee during ABL catalyzed hydrolysis of (±)-2.

(±)-2) was reduced from 36 h to 20 h, besides, there was an appreciable enhancement in the enantioselectivity as depicted in Table 2. The significant increase of enantioselectivity factor (E) from 27.6 to 181.7 also underscores the importance of this approach in optimizing the reaction conditions. The HPLC graphs of racemic as well as resolved products are depicted in Fig. 1. The conversion (%) and enantiomeric excess (ee %) of the enzyme catalyzed hydrolysis were determined using chiral HPLC, employing chiral column Chiralcel OJ-H with mobile phase 2:98:0.1: iso-propanol:n-hexane:glacial acetic acid at a flow rate 1.5 ml/min. The absolute configuration of the final product was established by comparing the sign of optical rotation with that reported in the literature [14]. The ratio of co-solvent used with respect to buffer also played an important role during enzymatic hydrolysis of (±)-2, using celite as a solid support. As shown in Fig. 2, the addition of 20% DMSO resulted in improved conversion with high enantioselectivities. 3. Conclusions In conclusion racemic BINOL was successfully resolved by Arthrobacter sp. lipase (ABL) catalyzed hydrolysis of the mono acetate. The novel approach of using immobilized substrate on the surface of celite [1:5; substrate:support (w/w)] and addition of 20%

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DMSO resulted in a significant improvement in rate of hydrolysis as well as enantioselectivity at 20 g/L concentration of the substrate. The methodology of using an inert support for improving the kinetic resolution may find further applications in the lipase/esterase catalyzed resolution of other substrates of economical importance. 4. Experimental 4.1. General experimental 1 H NMR and 13 C NMR spectra in CDCl were recorded on Bruker 3 ARX 200 spectrometers (200 MHz 1 H, 50 MHz 13 C) with TMS as an internal standard. Chemical shifts are expressed in parts per million (␦ ppm); J values are given in Hertz. Reagents and solvents used were mostly LR grade. Silica gel coated aluminum plates from M/s Merck were used for TLC. MS were recorded on Jeol MSD-300 and Brucker Esquire 3000 GC-Mass spectrometer. IR was recorded on a FT-IR Bruker (270-30) spectrophotometer. Elemental analyses were performed on Elementar Vario EL-III. Optical rotations were measured on Perkin-Elmer 241 polarimeter at 25 ◦ C using sodium D light. Enantiomeric excess (ee) was determined on a chiral stationary phase HPLC column.

4.2. Synthesis of 1-(2-hydroxynapthalen-1-yl)napthalen-2-yl acetate (±)-(2): (C22 H16 O3 ) Dimethyl amino pyridine (17.1 mg, 0.139 mmol) and acetic anhydride (392 mg, 3.84 mmol) at 0 ◦ C were added to a solution of 1,1 -binaphthyl-2,2 -diol (1.00 g, 3.49 mmol) in a mixture of toluene (15 mL), CH2 Cl2 (10 mL) and pyridine (3 mL). The mixture was stirred at room temperature for 6 h and the solvent was removed in vacuo. The residue was dissolved in ether (25 mL), successively washed with 2 N HCl (20 mL), sat. NaHCO3 (20 mL) and brine (20 mL) and then dried (anhydrous Na2 SO4 ). Evaporation and silica gel column chromatography (EtOAc: Hexane; 2:98) gave 1-(2-hydroxynapthalen-1-yl)napthalen-2-yl acetate (±)-2 (1.02 g, 89%). Colorless crystals; mp 125–127 ◦ C; IR (KBr) cm−1 : 1230, 1740, 3460. 1 H NMR, ␦: 1.86 (s, 3H, CH3 CO), 5.22 (s, 1H, OH), 7.03 (d, J = 8.2 Hz, ArH), 7.23–7.26 (m, 2H, ArH), 7.31–7.35 (m, 3H, ArH), 7.40 (d, J = 8.5 Hz, ArH), 7.50 (t, J = 7.5 Hz, 1H, ArH), 7.85 (d, J = 8.0 Hz, ArH), 7.91 (d, J = 8.5 Hz, 1H, ArH), 7.97 (d, J = 8.5 Hz, 1H, ArH), 8.07 (d, J = 9.0 Hz, 1H, ArH). 13 C NMR, ␦ 20.1, 114.1, 118.3, 121.8, 123.2, 123.6, 124.6, 125.8, 126.4, 126.7, 127.5, 128.1, 128.4, 129.1, 130.4, 130.8, 132.3, 133.5, 133.6, 148.1, 151.8, 170.4. ESI-MS (m/z): 328. Anal. Calc. for C22 H16 O3 : C, 80.47; H, 4.91. Found C, 80.52; H, 4.96. 4.3. Synthesis of 1-(2-hydroxynapthalen-1-yl)napthalen-2-yl propionate (±)-(3): (C23 H18 O3 ) 1-(2-Hydroxynapthalen-1-yl)napthalen-2-yl propionate (±)-3 (3.07 g, 90%) was prepared from [1,1 ]-binaphthalenyl-2,2 -diol (2.86 g, 10 mmol) using the same procedure as applied for (±)-2 as colorless crystals, mp. 140–142 ◦ C; IR (KBr) cm−1 : 1146, 1749, 3441; 1 H NMR, ı: 0.69 (t, J = 7.6 Hz, 3H, CH ), 2.00–2.18 (m, 2H, CH CO), 3 2 7.04 (d, J = 8.0 Hz, 1H, ArH), 7.21–7.55 (m, 7H), 7.85 (d, J = 9.0 Hz, 1H, ArH), 7.90 (d, J = 9.3 Hz, 1H, ArH), 7.98 (d, J = 8.2 Hz, 1H, ArH), 8.08 (d, J = 8.8 Hz, 1H, ArH). 13 C NMR, ı: 8.5, 27.4, 114.2, 118.3, 121.9, 123.1, 123.6, 124.6, 125.7, 126.3, 126.7, 127.5, 128.0, 128.4, 129.1, 130.4, 130.8, 132.3, 133.6, 148.2, 151.8, 173.8. ESI-MS (m/z): 342. Anal. Calc. for C23 H18 O3 : C, 80.68; H, 5.30. Found C, 80.62; H, 5.28. 4.4. Synthesis of 1-(2-hydroxynapthalen-1-yl)napthalen-2-yl butyrate (±)-(4): (C24 H20 O3 ) 1-(2-Hydroxynapthalen-1-yl)napthalen-2-yl butyrate (±)-4 (3.13 g, 88%) was prepared from 1,1 -binaphthyl-2,2 -diol (2.86 g,

10 mmol) using the same procedure as applied for (±)-2; mp 136–138 ◦ C, IR (KBr) cm−1 : 1170, 1730, 3410; 1 H NMR, ı: 0.57 (t, J = 7.4 Hz, 3H, CH3 ), 1.21 (sex, J = 7.3 Hz, 2H, CH2 ), 2.04–2.17 (m, 2H, CH2 CO), 7.04 (d, J = 8.2 Hz, 1H, ArH), 7.23–7.41 (m, 6H, ArH), 7.51 (t, J = 7.5 Hz, 1H, ArH), 7.84 (d, J = 8.0 Hz, 1H, ArH), 7.90 (d, J = 9.0 Hz, 1H, ArH), 7.97 (d, J = 8.5 Hz, 1H, ArH), 8.07 (1H, d, J = 9.0 Hz, ArH); 13 C NMR, ı: 13.1, 18.1, 35.7, 114.2, 118.3, 121.8, 122.8, 123.5, 124.5, 125.7, 126.3, 126.7, 127.5, 127.9, 128.3, 129.0, 130.4, 130.8, 131.3,133.5, 147.2, 152.1, 174.1. ESI-MS (m/z): 356. Anal. Calc. for C24 H20 O3 : C, 80.88; H, 5.66. Found C, 80.89; H, 5.68. 4.5. Synthesis of (S)- 1,1 -binaphthyl-2,2 -diol [(S)-1] DMSO (500 ␮L) was slowly added to aqueous phosphate buffer suspension (2.5 ml, 0.1 M, pH 7.0) comprising (±)-1(2-hydroxynapthalen-1-yl)napthalen-2-yl acetate (±)-2 (50 mg) adsorbed on celite (250 mg). Wet pallet comprising whole cells of Arthrobacter sp. (100 mg) were added to above suspension. The reaction mixture was placed on an orbital shaker with continuous shaking (250 rpm) at 25 ◦ C. Thin layer chromatography and chiral high performance liquid chromatography (HPLC) were carried to monitor the reaction. After a certain degree of conversion (∼37%) the reaction was terminated by adding ethyl acetate and was extracted with ethyl acetate (3× 10 mL). The organic layer was combined and washed with water. The combined organic layer was then dried and evaporated under reduced pressure to furnish a mixture comprising hydrolyzed alcohol and unhydrolyzed ester, which was separated by column chromatography using petroleum ether and acetone (98:2) as eluent giving (R)-(+)-1-(2-hydroxynapthalen-1◦ yl)napthalen-2-yl acetate, ee = 60.4%, [˛]25 D = +18.5 (c 0.25, THF) 25 ◦ (lit. [14] [˛]D = +31.0 (c 1.21, THF), ee = 95%); and (S,S)-(-)-1,1 ◦ binaphthyl-2,2 -diol, [˛]25 D = −30.0 (c 0.25, THF), ee 98%; (lit. [14] 25 ◦ [˛]D = −28.0 (c 1.05, THF), ee = 89%). 4.6. Synthesis of 1-(2-acetoxynapthalen-1-yl)napthalen-2-yl acetate (±)-(5): (C24 H18 O4 ) Acetic anhydride (1.2 g, 12 mmol) and catalytic amount of DMAP were added to a solution of 1,1 -binaphthyl-2,2 -diol (±)1 (1.43 g, 5 mmol) in dry dichloromethane and the reaction mixture kept overnight at room temperature. The contents of reaction mixture were poured in ice-cold water and extracted with dichloromethane. The organic layer was washed, dried and evaporated to get 1-(2-acetoxynapthalen-1-yl)napthalen-2-yl acetate (±)-5 (1.62 g, 95%). IR (KBr) cm−1 : 1191.2, 1367.4, 1763.1, 3061.6. 1 H NMR, ı: 1.85 (s, 6H, COCH ), 7.15–7.33 (m, 4H, ArH), 7.40–7.50 3 (m, 4H, ArH), 7.91 (d, J = 8.1 Hz, 2H, ArH), 8.00 (d, J = 9.9 Hz, 2H, ArH). 13 C NMR, ı: 20.6, 121.9, 123.5, 125.7, 126.3, 126.8, 128.1, 129.6, 131.6, 133.4, 146.8, 169.4. ESI-MS (m/z): 370. Anal. Calc. for C24 H18 O4 : C, 77.82; H, 4.90. Found C, 77.89; H, 4.88. 4.7. Preparation of ABL Arthrobacter sp. cell biomass was prepared in shake flasks and in a 10 L fermentor containing medium (1% peptone, 0.5% NaCl and 0.5% beef extract, pH 7.0). The medium was inoculated with an overnight preculture prepared in the same broth. The culture was grown at 30 ◦ C for 16–18 h at 200 rpm. The cell pellet was separated from the broth by centrifugation at 10,000 × g for 15 min at 4 ◦ C and was preserved at −20 ◦ C until further use. Arthrobacter sp. microbial culture (ABL, MTCC no. 5125), isolated at institute has been deposited in the MTCC culture collection under the Budapest Treaty (2004) [24].

P. Gupta et al. / Journal of Molecular Catalysis B: Enzymatic 101 (2014) 35–39

Acknowledgement The authors (PG and NM) are highly thankful to Principal, GDC Kathua and Higher Education Department, Jammu and Kashmir for their support.

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