Tetrahedron: Asymmetry xxx (2013) xxx–xxx

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Tetrahedron: Asymmetry

journal homepage: www.elsevier .com/locate / tetasy

Enzymatic transesterification of pharmacologically interestingb-aminocycloalkanol precursors

N

OH

OO

O

NH

N

N

NN

HN

O

NH2

OO

N

N

N

OH

NHO

HN

O

OH

Vernakalant (antiarrhythmic) Spleen tyrosine kinase in

Indinavir (inhibitor of HIV protease)

Figure 1. Examples of bioactive molecules.

0957-4166/$ - see front matter � 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.tetasy.2013.08.007

⇑ Corresponding author. Tel.: +34 985259021.E-mail address: fmv@entrechem.com (F. Morís).

Please cite this article in press as: González-Sabín, J.; et al. Tetrahedron: Asymmetry (2013), http://dx.doi.org/10.1016/j.tetasy.2013.0

Javier González-Sabín a, Nicolás Ríos-Lombardía a, Vicente Gotor b, Francisco Morís a,⇑a EntreChem, SL, Edificio Científico Tecnológico, Campus El Cristo, 33006 Oviedo, Spainb Departamento de Química Orgánica e Inorgánica, Universidad de Oviedo, 33071 Oviedo, Spain

a r t i c l e i n f o a b s t r a c t

Article history:Received 2 August 2013Accepted 13 August 2013Available online xxxx

Chemoenzymatic syntheses of both enantiomers of cis- and trans-2-aminocyclopentanol as well as cis-and trans-2-aminocyclohexanol, which are valuable building blocks for a plethora of ligands and pharma-ceuticals have been efficiently carried out. The strategy involves the stereospecific syntheses of racemicaminocycloalkanol precursors via tagging of a phthalimide as a masking group and subsequent lipase-catalyzed kinetic resolution. Most of the lipases exhibited excellent enantioselectivity (E� 200) in thetransesterification reactions of trans-derivatives, with both N-protected (R,R)-amino acetates and (S,S)-amino alcohols being isolated in enantiopure form. With regard to cis-derivatives, lipases were also veryselective, even though the biotransformations were significantly slower.

� 2013 Elsevier Ltd. All rights reserved.

NH2

hibitor

1. Introduction

The b-amino alcohol moiety is ubiquitous in nature. The subfam-ily of b-aminocycloalkanols can be found in many natural productsand synthetic bioactive molecules such as the antiarrhythmic ver-nakalant or the inhibitors of HIV (indinavir) and spleen tyrosine ki-nase (Syk) depicted in Figure 1.1 Furthermore, they have alsofound great application in asymmetric catalysis as auxiliaries orligands.2 Due to their inherent interest, a vast number of methodshave been developed over the last two decades in order to obtainthese compounds in enantiomerically pure form, including thederivatization of naturally occurring amino acids, asymmetric ami-no hydroxylation of olefins or resolution of racemic mixturesemploying biocatalysts or via crystallization of diastereomeric saltsprepared from optically active carboxylic and phosphoric acids.Regarding enzymatic methods, the lipase-catalyzed acylation ordeacylation has proved to be one of the most efficient alternativesto reach these compounds. Many years ago, the enzymatic acylationof unprotected b-aminocycloalkanols turned out to be challenging,undergoing undesired migration processes and leading to poorenantioselectivies.3 However, these problems could be circum-vented by employing as substrates different precursors such asb-azido- or b-nitrocycloalkanols,4,5 or N-protected derivatives (car-bamates or tertiary amines).3,6 Very recently, Taneja et al.7 reporteda efficient enzymatic method to prepare enantiopure trans-1,2-aminocycloalkanols and trans-1,2-aminoindanols via hydrolysisof the corresponding N-phthalimido acetates. Thus, the use of the

phthalimide moiety as a masking group for the free amino groupwas very advantageous since it allowed easy attachment andcleavage, and also provided derivatives which were recognized bythe enzymes with excellent selectivity. Herein we report a comple-mentary approach based on the direct lipase-catalyzed acylation oftrans-2-phthalimidocycloalkanols as well as the correspondingcis-isomers.

8.007

Table 1Enzymatic transesterification of (±)-trans-3a and (±)-trans-3ba

n = 1, (±)-trans-3a

n = 2, (±)-trans-3bn = 1, (R,R)-trans-4an = 2, (R,R)-trans-4b

n = 1, (S,S)-trans-3an = 2, (S,S)-trans-3b

OH

N

O

O

n

AcOCH=CH2

lipase, TBME

OAc

N

O

O

n

OH

N

O

O

n+

Entry Compd Lipase t (h) cb (%) eesc (%) eep

c (%) Ed

1 trans-3a CAL-B 24 46 85 >99 >2002 trans-3a CAL-A 24 4 1 21 13 trans-3a AK 24 51 >99 97 >2004 trans-3a RM IM 24 51 >99 98 >2005 trans-3a PS IM 24 50 >99 >99 >2006 trans-3b CAL-B 24 16 19 >99 >2007 trans-3b CAL-A 24 2 2 >99 >2008 trans-3b AK 24 35 55 >99 >200

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2. Results and discussion

2.1. Synthesis of racemic compounds (±)-trans-3a,b and(±)-cis-3a,b

The synthesis of racemic trans-2-phthalimidocycloalkanols (±)-trans-3a and (±)-trans-3b was easily accomplished in two stepsfollowing the procedure previously described (Scheme 1).7 Thus,the corresponding epoxide 1a,b was opened with ammonia andthe resulting trans-2-aminocycloalkanol (±)-2a,b condensed withphthalic anhydride. After work-up, (±)-trans-3a and (±)-trans-3bwere isolated in a state of purity (yield >80%) and could be em-ployed in the enzymatic transesterification without further purifi-cation. Regarding the cis isomers (±)-cis-3a and (±)-cis-3b, thesewere obtained respectively from (±)-trans-3a and (±)-trans-3b viaMitsunobu inversion8 of the secondary alcohol. Once purified byflash chromatography, racemic cis-2-phthalimidocycloalkanolswere isolated in moderate yields (40–60%).

n = 1, (±)-trans-3an = 2, (±)-trans-3b

n

OH

NH2n

OH

N

O

O

n

Oi

n = 1, (±)-cis-3a

n = 2, (±)-cis-3b

OH

N

O

O

n

iii, iv

ii

n = 1, 1an = 2, 1b

n = 1, (±)-2an = 2, (±)-2b

Scheme 1. Reagents and conditions: (i) concd aq NH3 in MeOH, rt; (ii) phthalicanhydride, Et3N, toluene, reflux; (iii) DEAD, PPh3, p-nitrobenzoic acid, THF; (iv) 1 NNaOH in MeOH, rt.

9 trans-3b RM IM 24 50 >99 >99 >20010 trans-3b PS IM 24 50 >99 >99 >200

a Reactions carried out at 30 �C and 250 rpm, with a 1:3 molar ratio substrate/acyl donor.

b c ¼ ees=ðees þ eepÞ.c Enantiomeric excess determined by chiral HPLC.d E ¼ ln½ð1� cÞ � ð1� eesÞ�= ln½ð1� cÞ � ð1þ eepÞ�.

2.2. Enzymatic resolution of racemic trans-2-phthalimidocyclo-alkanols (±)-trans-3a and (±)-trans-3b

First, we studied the kinetic resolution of trans-2-phthalimidocycloalkanols (±)-trans-3a and (±)-trans-3b by means of a lipase-cat-alyzed transesterification reaction. Previously, this methodology hasbeen successfully applied to other trans-b-substituted cycloalkanolsbearing functional groups such as azides,4 halides,9 carbamates3 ortertiary amines.5,10 Based on this background, we performed the bio-transformations using a threefold excess of vinyl acetate and tert-butyl methyl ether (TBME) as the acyl donor and solvent, respec-tively, and testing a set of five biocatalysts: lipase B from Candidaantarctica (CAL-B), lipase A from Candida antarctica (CAL-A), lipasefrom Rhizomucor miehei (RM IM), lipase from Pseudomonas fluores-cens (AK), and lipase from Pseudomonas cepacia (PS IM). As can bededuced from Table 1, in the case of the cyclopentylic derivative(±)-trans-3a all of the lipases were highly enantioselective withthe exception of CAL-A (entries 1–5). Thus, after one day of reactionthe other four biocatalysts led to conversions very close to 50% andvery high enantioselectivities (E >200). For example, PS IM lipase ledto an optimal process in which both the substrate and product wereisolated in enantiopure form (ee >99%) to a conversion of 50% (entry5). On the contrary, CAL-A showed very low activity and no selectiv-ity (entry 2). Similarly, all of the selected lipases displayed excellentenantioselectivities (E >200) toward the homolog trans-2-phthalim-idocyclohexanol (±)-trans-3b (entries 6–10). Particularly, CAL-B and

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AK led to slightly lower conversion compared to the reactions per-formed with (±)-trans-3a, and CAL-A showed high enantioselectivitydespite very low conversion (entry 7). The assignment of the (1S,2S)-configuration for the remaining N-protected aminocycloalkanolstrans-3a,b and (1R,2R) for the acetates formed trans-4a,b was estab-lished by comparison of the sign of its specific rotation with re-ported values.7 This means that tested lipases preferentiallycatalyzed the acetylation of the (1R)-alcohol, following Kazlauskas’rule.11 It is worth noting not only the high enantioselectivity but alsothe yields obtained after chromatographic separation of the reactionmixture. Thereby, under the optimal conditions (entries 5, 9, and10), both (1R,2R)-alcohols and (1R,2R)-acetates were isolated inenantiopure form (ee >99%) from the same biotransformation withyields higher than 45% (50% is the limiting yield for a kineticresolution).

The PS IM-catalyzed transesterification of (±)-trans-3a (entry 5)was selected to perform a recycling study of the biocatalyst. Thus,after five cycles no loss of activity or enantioselectivity was ob-served, maintaining c = 50% and enantiomeric excesses >99% forboth substrate and product after 24 h of reaction. Likewise, thisprocess was successfully scaled-up (1 g scale at 0.2 M) and despitea significant reduction of the lipase amount (1:10 wt/wt ratio tosubstrate), the optimal conversion of 50% was reached after 48 h.

2.3. Enzymatic resolution of racemic cis-2-phthalimidocyclo-alkanols (±)-cis-3a and (±)-cis-3b

After successful resolution of the trans-2-phthalimidocycloalka-nols, we turned our attention to the cis diastereomers (±)-cis-3aand (±)-cis-3b. We therefore performed the transesterification pro-cesses under identical reaction conditions to those describedabove. In the case of the cyclopentyl derivative cis-3a, the resultsobtained were excellent with all of the lipases (Table 2, entries1–5). Thereby, with the exception of CAL-B which exhibited loweractivity (entry 1), the other lipases allowed us to reach a conver-sion value of 50% after 24 h, with both the substrate and productbeing isolated with ee >99%. Regarding the cyclohexyl cis-deriva-tive 3b, the lipases showed a notable decrease in their activity(c <30%) although they maintained excellent enantioselectiontoward the formation of the acetate (R,S)-4b (entries 7–10). In

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Table 2Enzymatic transesterification of (±)-cis-3a and (±)-cis-3ba

n = 1, (±)-cis-3a

n = 2, (±)-cis-3bn = 1, (R,S)-cis-4a

n = 2, (R,S)-cis-4bn = 1, (S,R)-cis-3a

n = 2, (S,R)-cis-3b

OH

N

O

O

n

AcOCH=CH2

lipase, TBME

OAc

N

O

O

n

OH

N

O

O

n+

Entry Compd Lipase t (h) cb (%) eesc (%) eep

c (%) Ed

1 cis-3a CAL-B 24 28 38 >99 >2002 cis-3a CAL-A 24 50 >99 >99 >2003 cis-3a AK 24 50 >99 >99 >2004 cis-3a RM IM 24 50 >99 >99 >2005 cis-3a PS IM 24 50 >99 >99 >2006 cis-3b CAL-B 24 <1 — — —7 cis-3b CAL-A 24 3 3 >99 >2008 cis-3b AK 24 6 61 >99 >2009 cis-3b RM IM 24 14 17 >99 >20010 cis-3b PS IM 24 26 35 >99 >20011 cis-3b PS IM 72 41 69 >99 >20012e cis-3b PS IM 72 50 >99 >99 >200

a Reactions carried out at 30 �C and 250 rpm, with a 1:3 molar ratio substrate/acyl donor.

b c ¼ ees=ðees þ eepÞ.c Enantiomeric excess determined by chiral HPLC.d E ¼ ln½ð1� cÞ � ð1� eesÞ�= ln½ð1� cÞ � ð1þ eepÞ�.e Reaction temperature: 45 �C.

J. González-Sabín et al. / Tetrahedron: Asymmetry xxx (2013) xxx–xxx 3

the particular case of CAL-B, this lipase did not show any activity(entry 6). In order to reach a higher conversion, the biotransforma-tion catalyzed by the most active lipase, that is, PS IM, was allowedto react during 72 h (entry 11) to provide c = 41%. Finally, the opti-mal conversion of 50% was achieved for 72 h with a higher temper-ature (45 �C), with both (R,S)-4b and (S,R)-3b being isolated inenantiomerically pure form. The assignment of the (1R,2S)-config-uration for the resulting acetates cis-4a,b was established by com-parison of the sign of its specific rotation with the reported valuesfor (1R,2S)-2-aminocyclopentanol hydrochloride and (1R,2S)-2-aminocyclohexanol hydrochloride,12 with previous cleavage ofboth acetate and phthalimido groups followed by derivatizationas a hydrochloride salt. Again, the lipases exhibited a preferencefor the (1R)-alcohol, according to the Kazlauskas’ rule.11

The lower reactivity of the lipases toward the cis isomerscompared to the trans-counterpart could be expected accordingto previous reports with other b-substituted cycloalkanols, andcould arise from the presence of a bulkier substituent (NH-Phth)on the same face as the reacting hydroxyl group.10,13

3. Conclusion

The cis- and trans-diastereomers of 2-phthalimidocyclopenta-nol and 2-phthalimidocyclohexanol were resolved by lipase-cata-lyzed transesterification reactions. The processes were highlyeffective in terms of both chemical yields and enantiomeric excessof the final products. The PS IM lipase turned out to be the bestbiocatalyst, showing complete selectivity toward the four sub-strates. Likewise, this lipase was employed satisfactorily for recy-cling and scaling-up studies with trans-3a as a model substrate.

4. Experimental

4.1. General

Lipase B from Candida antarctica (CAL-B) was a kind gift fromNovo Nordisk. Lipase A from Candida antarctica (CAL-A) was

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purchased from c-LEcta. Lipase PS IM was purchased from AmanoPharmaceutical Co. Lipases from Pseudomonas fluorescens (AK) andRhizomucor miehei (Lipozyme RM IM) were purchased from Sigma–Aldrich. For the enzymatic reactions, tert-butyl methyl ether ofspectrophotometric grade (stored with 4 Å molecular sieves) andcommercial vinyl acetate were used. Thin-layer chromatographywas performed on precoated TLC plates of Merck silica gel60F254, using potassium permanganate as a developing reagent.For column chromatography, Merck silica gel 60 (particle size,40–63 lm) was used. Optical rotations were measured using a Per-kin–Elmer 343 polarimeter. ESI+ experiments were carried out torecord mass spectra on a Hewlett-Packard 1100 HPLC/MS (electro-spray) instrument. High-resolution mass spectra (HRMS) were re-corded in ESI+ mode. 1H NMR and proton-decoupled 13C NMRspectra (CDCl3 solutions) were obtained using AV-300 or DPX-300 (1H, 300.13 MHz and 13C, 75.5 MHz) spectrometers using thed scale (ppm) for chemical shifts; calibration was made on theCDCl3 (13C; 76.95 ppm) or the residual CHCl3 (1H; 7.26 ppm) sig-nals. Chiral HPLC analyses were performed using Chiralcel OJ-H,Chiralcel OD and Chiralpak AS (Chiral Technologies) columns.

4.2. General procedure for the synthesis of (±)-trans-2-phtha-limidocycloalkanols (±)-trans-3a and (±)-trans-3b

To a mixture of the corresponding cycloalkene oxide 1a,b(0.1 mol) and 25% NH3 aq (1 mol), methanol was added until com-plete dissolution. The reaction mixture was then stirred overnightfor cyclohexene oxide 1b or 5 days for cyclopentene oxide 1a. Next,the solvents were evaporated under reduced pressure and theresulting trans-2-aminocycloalkanol 2a,b was submitted to the fol-lowing step without further purification. Thus, phthalic anhydride(0.1 mol), toluene (100 mL) and a catalytic amount of triethyl-amine were added to the previous crude mixture and the solutionwas refluxed overnight. After cooling to room temperature, thereaction mixture was extracted twice with water and brine. The or-ganic layer was concentrated under reduced pressure to yieldcrude trans-2-phthalimidocycloalkanol. Further purification byflash chromatography (hexane:AcOEt mixtures) provided pure(±)-trans-2-phthalimidocyclopentanol 3a (yield >85%) or (±)-trans-2-phthalimidocyclohexanol 3b (yield >80%).

4.3. General procedure for the synthesis of (±)-cis-2-phthalimi-docycloalkanols (±)-cis-3a and (±)-cis-3b

To a solution of the corresponding (±)-trans-2-phthalimidocy-cloal kanol (10.0 mmol) in dry THF (100 mL) at 0 �C under a nitrogenatmosphere, the following solutions were successively added:triphenylphosphine (20.0 mmol), p-nitrobenzoic acid (20.0 mmol)and diethyl azodicarboxylate (20.0 mmol). The resulting yellowsolution was stirred at room temperature overnight. Next, the or-ganic solvent was evaporated under reduced pressure and the crudeobtained purified by flash chromatography (hexane:AcOEt mix-tures), affording the corresponding p-nitrobenzoate ester. This inter-mediate was subsequently hydrolyzed by treatment with 1 M NaOHin methanol (30 mL) until the disappearance of the starting material(TLC control, hexane:AcOEt 2:1). Next, methanol was removed andthe residue extracted with H2O (30 mL) and dichloromethane(3 � 20 mL). The organic phases were combined, dried over Na2SO4,and the solvent evaporated under reduced pressure. Further purifi-cation by flash chromatography (hexane:AcOEt mixtures) providedpure (±)-cis-2-phthalimidocyclopentanol 3a (60%) or (±)-cis-2-phthalimidocyclohexanol 3b (40%).

4.3.1. (±)-cis-2-Phthalimidocyclopentanol (±)-cis-3aYield: 60%; mp 71–73 �C; 1H NMR (300 MHz): d 1.50–1.70 (m,

1H), 1.80–2.10 (m, 4H), 2.40–2.60 (m, 1H), br s (1H, OH), 4.33 (q,

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4 J. González-Sabín et al. / Tetrahedron: Asymmetry xxx (2013) xxx–xxx

1H, J = 7.5 Hz), 4.53 (m, 1H), 7.71–7.75 (m, 2H), 7.82–7.90 (m, 2H);13C NMR (75.5 MHz) d 20.7 (CH2), 25.9 (CH2), 34.3 (CH2), 55.0 (CH),73.7 (CH), 123.3 (2 � CH), 131.9 (2 � C), 134.1 (2 � CH), 169.8(2 � C@O); MS (ESI+) m/z (rel intensity): 232.1 (M+H)+, 100; HRMS(ESI+) calcd for C13H14NO3 [M+H]+ 232.0968; found 232.0959.

4.3.2. (±)-cis-2-Phthalimidocyclohexanol (±)-cis-3bYield: 40%; mp 149–151 �C; 1H NMR (300 MHz): d 1.40–1.65

(m, 4H), 1.75–2.05 (m, 3H), 2.52 (qd, 1H, J = 3.9, 12.3 Hz), 4.19(br s, 1H), 4.31 (ddd, 1H, J = 1.9, 3.6, 13.1 Hz), 4.40 (br s, 1H, OH),7.73–7.78 (m, 2H), 7.82–7.90 (m, 2H); 13C NMR (75.5 MHz) d18.6 (CH2), 24.3 (CH2), 26.0 (CH2), 32.8 (CH2), 56.1 (CH), 69.1(CH), 123.5 (2 � CH), 131.7 (2 � C), 134.3 (2 � CH), 169.7(2 � C@O); MS (ESI+) m/z (rel intensity): 246.1 (M+H)+, 100,268.2 (M+Na)+, 30; HRMS (ESI+) calcd for C14H16NO3 [M+H]+

246.1125; found 246.1136.

4.4. Enzymatic transesterification of racemic cis- and trans-2-phthalimidocycloalkanols. General procedure

At first, tert-butyl methyl ether (1.0 mL) and vinyl acetate(3 equiv, 0.6 mmol, 37 lL) were added to a mixture of the racemicN-protected amino alcohol (0.20 mmol), lipase (1:1 wt/wt ratio tosubstrate) and 4 Å molecular sieves (5 mg). The suspension wasshaken at 30 �C and 250 rpm. The enzyme was then filtered,washed with tert-butyl methyl ether and the solvents were evapo-rated. Both the remaining N-protected amino alcohol and the N-protected amino acetate present in the residue were separatedby flash chromatography (hexane:AcOEt mixtures) and isolatedin yields higher than 90% (referred to the corresponding conversionvalue).

4.4.1. (1S,2S)-trans-2-Phthalimidocyclopentanol (1S,2S)-trans-3a½a�20

D ¼ þ42:1 (c 1.0, CHCl3) >99% ee.

4.4.2. (1R,2R)-trans-2-Phthalimido-1-acetoxycyclopentane(1R,2R)-trans-4a½a�20

D ¼ �51:0 (c 1.0, CHCl3) >99% ee.

4.4.3. (1S,2S)-trans-2-Phthalimidocyclohexanol (1S,2S)-trans-3b½a�20

D ¼ þ32:3 (c 1.0, CHCl3) >99% ee.

4.4.4. (1R,2R)-trans-2-Phthalimido-1-acetoxycyclohexane(1R,2R)-trans-4b½a�20

D ¼ �10:9 (c 1.0, CHCl3) >99% ee.

4.4.5. (1S,2R)-cis-2-Phthalimidocyclopentanol (1S,2R)-cis-3a½a�20

D ¼ �3:6 (c 0.50, CHCl3) >99% ee.

4.4.6. (1R,2S)-cis-2-Phthalimido-1-acetoxycyclopentane (1R,2S)-cis-4a

Mp 118–120 �C; ½a�20D ¼ þ8:8 (c 0.50, CHCl3) >99% ee; 1H NMR

(300 MHz): d 1.55–1.70 (m, 1H), 1.86 (s, 3H), 1.90–2.20 (m, 4H),2.82 (m, 1H), 4.65 (m, 1H), 5.27 (q, 1H, J = 6.0 Hz), 7.70–7.76 (m,2H), 7.82–7.88 (m, 2H); 13C NMR (75.5 MHz) d 20.9 (CH3), 21.2(CH2), 25.3 (CH2), 30.8 (CH2), 53.0 (CH), 74.6 (CH), 123.1(2 � CH), 131.8 (2 � C), 134.0 (2 � CH), 168.6 (C@O), 170.5(2 � C@O); MS (ESI+) m/z (rel intensity): 274.1 (M+H)+, 80, 296.2(M+Na)+, 20; HRMS (ESI+) calcd for C15H16NO4 [M+H]+ 274.1074;found 274.1081.

4.4.7. (1S,2R)-cis-2-Phthalimidocyclohexanol (1S,2R)-cis-3b½a�20

D ¼ �11:5 (c 0.50, CHCl3) >99% ee.

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4.4.8. (1R,2S)-cis-2-Phthalimido-1-acetoxycyclohexane (1R,2S)-cis-4b

Mp 130–132 �C; ½a�20D ¼ �12:0 (c 0.50, CHCl3) >99% ee; 1H NMR

(300 MHz): d 1.35–1.80 (m, 5H), 1.90–2.01 (m, 2H), 2.03 (s, 3H),3.04 (qd, 1H, J = 3.7, 13.3 Hz), 4.28 (ddd, 1H, J = 2.5, 3.8, 13.3 Hz),5.27 (br s, 1H), 7.73–7.78 (m, 2H), 7.82–7.90 (m, 2H); 13C NMR(75.5 MHz) d 19.7 (CH2), 21.2 (CH3), 24.0 (CH2), 25.8 (CH2), 30.1(CH2), 53.8 (CH), 70.8 (CH), 123.1 (2 � CH), 131.8 (2 � C), 133.9(2 � CH), 168.6 (C@O), 171.1 (2 � C@O); MS (ESI+) m/z (rel inten-sity): 288.2 (M+H)+, 50, 310.1 (M+Na)+, 40; HRMS (ESI+) calcd forC16H18NO4 [M+H]+ 288.1230; found 288.1224.

4.5. HPLC analyses

Chiralcel OJ-H, Chiralcel OD and Chiralpak AS columns wereused. UV detection, k = 210 nm.

4.5.1. (±)-trans-2-Phthalimidocyclopentanol (±)-trans-3aChiralcel OJ-H, hexane:2-propanol 95:5; 0.8 mL/min, 30 �C.

tR = 34.2 (R,R) and 39.0 (S,S) min RS = 1.5.

4.5.2. (±)-trans-2-Phthalimido-1-acetoxycyclopentane (±)-trans-4a

Chiralcel OJ-H, hexane:2-propanol 95:5; 0.8 mL/min, 30 �C.tR = 15.7 (R,R) and 25.1 (S,S) min RS = 9.3.

4.5.3. (±)-trans-2-Phthalimidocyclohexanol (±)-trans-3bChiralcel OJ-H, hexane:2-propanol 80:20; 0.6 mL/min, 20 �C.

tR = 10.7 (R,R) and 11.5 (S,S) min RS = 1.8.

4.5.4. (±)-trans-2-Phthalimido-1-acetoxycyclohexane (±)-trans-4b

Chiralcel OJ-H, hexane:2-propanol 80:20; 0.6 mL/min, 20 �C.tR = 12.7 (S,S) and 14.4 (R,R) min RS = 3.4.

4.5.5. (±)-cis-2-Phthalimidocyclopentanol (±)-cis-3aChiralpak AS, hexane:2-propanol 90:10; 0.8 mL/min, 40 �C.

tR = 14.2 (S,R) and 17.6 (R,S) min RS = 8.3.

4.5.6. (±)-cis-2-Phthalimido-1-acetoxycyclopentane (±)-cis-4aChiralpak AS, hexane:2-propanol 90:10; 0.8 mL/min, 40 �C.

tR = 10.4 (R,S) and 20.1 (S,R) min RS = 15.0.

4.5.7. (±)-cis-2-Phthalimidocyclohexanol (±)-cis-3bChiralcel OD, hexane:2-propanol 90:10; 0.8 mL/min, 40 �C.

tR = 9.3 (S,R) and 10.1 (R,S) min RS = 2.0.

4.5.8. (±)-cis-2-Phthalimido-1-acetoxycyclohexane (±)-cis-4bChiralcel OD, hexane:2-propanol 90:10; 0.8 mL/min, 40 �C.

tR = 6.3 (S,R) and 7.0 (R,S) min RS = 1.7.

Acknowledgment

We thank Novo Nordisk Co. for the generous gift of the CAL-B.

References

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