Fluorescence-based screening of asymmetric acylation catalysts through parallel enantiomer analysis. Identification of a catalyst for tertiary alcohol resolution

Article abstract of DOI:10.1021/jo015803z

A technique for high-throughput screening of kinetic resolution catalysts is reported. The method relies on carrying simultaneous kinetic resolutions in a multiwell plate format wherein each well contains a unique catalyst and a small amount of a pH-activated fluorescent sensor (3). By conducting experiments such that each catalyst is evaluated in parallel in the presence of each isolated enantiomer, an indication of catalyst activity is obtained on a per enantiomer basis. Catalysts that are highly active for one enantiomer but modestly active for another are then reevaluated in conventional kinetic resolutions. From these screens, a highly selective k_rel = 46) pentapeptide (4) was obtained for a model secondary alcohol (1). In addition, peptide 10 was found to afford excellent selectivities (k_rel > 20) for a number of alcohol substrates (9a-9f) in the traditionally challenging tertiary class.

Full text of DOI:10.1021/jo015803z

5522
J . Org. Chem. 2001, 66, 5522-5527
F lu or escen ce-Ba sed Scr een in g of Asym m etr ic Acyla tion Ca ta lysts
th r ou gh P a r a llel En a n tiom er An a lysis. Id en tifica tion of a Ca ta lyst
for Ter tia r y Alcoh ol Resolu tion
Elizabeth R. J arvo, Catherine A. Evans, Gregory T. Copeland, and Scott J . Miller*
Department of Chemistry, Merkert Chemistry Center, Boston College,
Chestnut Hill, Massachusetts 02467-3860
scott.miller.1@bc.edu
Received May 29, 2001
A technique for high-throughput screening of kinetic resolution catalysts is reported. The method
relies on carrying simultaneous kinetic resolutions in a multiwell plate format wherein each well
contains a unique catalyst and a small amount of a pH-activated fluorescent sensor (3). By
conducting experiments such that each catalyst is evaluated in parallel in the presence of each
isolated enantiomer, an indication of catalyst activity is obtained on a per enantiomer basis.
Catalysts that are highly active for one enantiomer but modestly active for another are then
reevaluated in conventional kinetic resolutions. From these screens, a highly selective (krel ) 46)
pentapeptide (4) was obtained for a model secondary alcohol (1). In addition, peptide 10 was found
to afford excellent selectivities (krel > 20) for a number of alcohol substrates (9a -9f) in the
traditionally challenging tertiary class.
Techniques that allow for the parallel preparation and
catalytic process, we planned high-throughput screens
of libraries of potential catalysts. However, our conven-
tional parallel screens were time-consuming because the
chiral GC assay that separates both enantiomers of 1 and
product 2 requires >30 min/reaction. To accelerate
catalyst identification, we developed a fluorescence-based
assay for catalyst activity.6 A fluorescent sensor (3) that
detects the acid byproduct generated during the reaction
is employed as an additive (2.5 mM, 25 mol %). This
allows for facile determination of the activity of multiple
catalysts simultaneously by performing parallel reactions
(in 96-well plates) in a commercially available fluores-
cence plate reader.
simultaneous screening of numerous catalysts have
gained particular attention as they promise to facilitate
catalyst discovery.1,2 Research in our laboratory has
focused on the discovery of low molecular weight peptides
that mimic enantioselective enzymes for use in asym-
metric organic synthesis.3 In particular, peptides contain-
ing the nucleophilic N-alkylimidazole moiety have been
found to function as effective catalysts for the kinetic
resolution of certain secondary alcohols.4 Kinetic resolu-
tions of 1 (eq 1) can be achieved with krel values > 50
To obtain information concerning relative rates of
reaction for two different enantiomers, we perform assays
in which each catalyst is screened for reactivity against
the isolated, optically pure enantiomers of the starting
material. Reetz and co-workers have previously applied
an IR thermography assay to isolated enantiomer screens
of libraries of enzymatic catalysts with notable success.7,8
In the present study, we use the fluorescence-based
reactivity assay in a spatially segregated enantiomer
screen that allows for direct measurement of catalytic
rates for the isolated enantiomers. A multiwell plate is
divided in half, with one enantiomer deposited in one-
half of the wells (e.g., 48 of the wells in a 96-well plate);
the other enantiomer is deposited in the remaining wells.
A fluorescence plate reader therefore allows a simulta-
neous determination of the relative rates of 48 catalysts
(96% ee for the recovered starting material at 52%
conversion).5 To expand the substrate scope for this
(1) J andeleit, B.; Schaefer, D. J .; Powers, T. S.; Turner, H. W.;
Weinberg, W. H. Angew. Chem., Int. Ed. 1999, 38, 2494.
(2) For recent reviews of combinatorial catalysis, see: (a) Reetz, M.
T. Angew. Chem., Int. Ed. 2001, 40, 284. (b) Kuntz, K. W.; Snapper,
M. L.; Hoveyda, A. H. Curr. Opin. Chem. Biol. 1999, 3, 313. (c) Francis,
M. B.; J amison, T. F.; J acobsen, E. N. Curr. Opin. Chem. Biol. 1998,
2, 422.
(3) Wong, C.-H.; Whitesides, G. M. Enzymes in Synthetic Organic
Chemistry; Elsevier Science Ltd.: Oxford, 1994.
(4) For reviews of catalytic kinetic resolution, see: (a) Keith, J . M.;
Larrow, J . F.; J acobsen, E. N. Adv. Synth. Catal. 2001, 343. 5. (b)
Hoveyda, A. H.; Didiuk, M. T. Curr. Org. Chem. 1998, 2, 537.
(5) J arvo, E. R.; Copeland, G. T.; Papaioannou, N.; Bonitatebus, P.
J .; Miller, S. J . J . Am. Chem. Soc. 1999, 121, 11638.
(6) Copeland, G. T.; Miller, S. J . J . Am. Chem. Soc. 1999, 121, 4306.
(7) Reetz, M. T.; Becker, M. H.; Kuhling, K. M.; Holzwarth, A.
Angew. Chem., Int. Ed. 1998, 37, 2647.
(8) For other reports of combinatorial techniques that allow high-
throughput assays for enantioselectivity, see: (a) Korbel, G. A.; Lalic,
G.; Shair, M. D. J . Am. Chem. Soc. 2001, 123, 361. (b) Guo, J .; Wu, J .;
Siuzdak, G.; Finn, M. G. Angew. Chem., Int. Ed. 1999, 38, 1755. (c)
Reetz, M. T.; Becker, M. H.; Klein, H.-W.; Stockigt, D. Angew. Chem.,
Int. Ed. 1999, 38, 1758.
10.1021/jo015803z CCC: $20.00 © 2001 American Chemical Society
Published on Web 07/12/2001

Catalyst Screens via Parallel Enantiomer Analysis
J . Org. Chem., Vol. 66, No. 16, 2001 5523
Ch a r t 1
4 effects substantially different rates of reaction for the
two enantiomers (Chart 1). The rate of the acylation of
the (R,R)-enantiomer (shown in red) is comparable to that
of the DMAP-catalyzed control reaction; the reaction of
the (S,S)-enantiomer (shown in blue) proceeds with a rate
comparable to that of the NMI-catalyzed reaction. Fur-
ther deconvolution of the superimposed data is shown
in Figure 1b. For example, catalyst 8 affords much less
difference in rate for the two enantiomers. The implica-
tion is that catalyst 4 will be a selective acylation catalyst
in a kinetic resolution performed on the racemate, while
catalyst 8 will be substantially less effective.13 Indeed,
rescreening of catalyst 4 with the racemate allows for a
rigorous determination of selectivity by conventional
chiral gas chromatography; catalyst 4 yields a substantial
krel of 46. Catalyst 8 affords a krel of 4. The selectivity
trends observed in the plate reader assay with other
catalysts also correlate well with those observed in
conventional GC assays in rescreening experiments. For
example, comparison of the fluorescence traces generated
with catalysts 4 and 5 suggests that catalyst 5, while less
selective than catalyst 4, should still exhibit considerable
rate differences for the two enantiomers. Indeed, catalyst
5 is appreciably selective, exhibiting a krel ) 37. Further
decreases in krel are observed with catalysts 6 and 7,
exhibiting selectivities of 17 and 6, respectively. Data
generated in this fashion underscore the subtle factors
within peptide structures that impact enantioselectivity.
With the validity of the approach established, we
turned our attention toward the resolution of tertiary
alcohols, a class that, to our knowledge, had been
previously unexplored in the area of nonenzymatic asym-
metric acylation catalysis.14 In fact, even biocatalytic
resolutions of tertiary carbinol centers are traditionally
F igu r e 1. Parallel screen of acylation catalysts for activity
and enantioselectivity. (a) Superimposed rate data on a single
plot. (R,R)-1 denoted (-), (S,S)-1 denoted (-). (b) Deconvolution
of raw fluorescence data plotted for unique catalysts with
respect to reactions of single enantiomers.
simultaneously when a 96-well plate is used (192 cata-
lysts when using a 384-well plate). Direct comparisons
thus give a qualitative measure of the relative rates for
the reactions of the two enantiomers with a wide variety
of catalysts simultaneously.
To validate this approach, a biased library of 60 tetra-
and pentapeptides that are capable of adopting â-turns
was synthesized in parallel.9-11 The catalysts were
cleaved from the resin, and the unpurified peptides were
used directly in screening assays.12 Substrate 1 was
evaluated as a test case. A sample of the data for an
individual screen of 60 different catalysts is shown in
Figure 1a. The rate profiles of three of the catalysts are
shown with bold curves.
Two points merit discussion: (i) The catalytic activities
of two control catalysts, N,N-(dimethylamino)pyridine
(DMAP, green curve) and N-methylimidazole (NMI, black
curve) parallel their well-established relative activities.
(ii) Indexed deposition of peptide catalysts in the various
wells allows for identification of those catalysts that
afford the greatest rate differences for the two enanti-
omers of the substrate. For example, the catalyst labeled
(9) For this purpose, the library was biased with D-Pro in the i+1
position for the majority of the peptides. See: (a) Haque, T. S.; Little,
J . C.; Gellman, S. H. J . Am. Chem. Soc. 1996, 118, 6975. (b) Karle, I.
L.; Awasthi, S. K.; Balaram, P. Proc. Natl. Acad. Sci. U.S.A. 1996, 93,
8189.
(10) The identity of each catalyst is listed in the Supporting
Information.
(11) Fru¨chtel, J . S.; J ung, G. Angew. Chem., Int. Ed. Engl. 1996,
35, 17.
(12) Catalyst identities were confirmed by ES/MS. Resynthesis and
full characterization of “hit” peptides was subsequently carried out.
See Supporting Information for details.
(13) Phenomena such as enantiomer-specific substrate or product
inhibition of the catalysts could lead to substantial differences in krel
for reactions performed on racemates vs those conducted on single
enantiomers. We have not observed large effects of this nature.

5524 J . Org. Chem., Vol. 66, No. 16, 2001
Ta ble 1. Kin etic Resolu tion s of Ter tia r y Alcoh ols w ith Ca ta lyst 10a
J arvo et al.
a
Reactions were carried out in PhMe (10 mol % of 10) and were quenched after 3 d. All data represent the average of 2-3 runs per
b
substrate. krel values determined according to the method of Kagan employing chiral HPLC or GC analyses. The fast-reacting enantiomer
is shown (9a -9f). See Supporting Information for details. c Substrate 9f reacts relatively slowly. These reactions were allowed to stir for
6 d.
difficult (krel values typically <10).15,16 Our results with
secondary alcohol acylation were promising for this
objective since catalytic activities greater than that
exhibited by DMAP had been observed, in an enantiomer-
specific context.17 We therefore conducted a screen analo-
gous to that described above for tertiary alcohol substrate
9a . Evaluation of the data indicated that imidazole-based
catalyst 10 would prove to be selective. Indeed, peptide
10 functions in the resolution of 9a (krel ) 11, 52%
conversion) when the reaction is conducted at 25 °C.
Conducting reactions at lower temperatures resulted in
enhanced krel values for 9a and a range of other tertiary
alcohol substrates (Table 1). For example, catalyst 10
affords krel ) 20 and 40 for substrate 9a at 4 and -23
°C, respectively (entry 1). Reaction rates are slow relative
to those observed for secondary alcohols. Nevertheless,
conversions of ∼40-50% can be achieved for this and
other tertiary alcohols within 72 h. p-Methyl-substituted
substrate 9b may be resolved with krel ) 22 at 4 °C;
selectivity is improved to krel > 50 at -23 °C (entry 2).
p-Nitro-substituted substrate 9c undergoes resolution
with krel ) 32 (entry 3, -23 °C). Naphthyl-substituted
substrate 9d affords a higher krel of 40 under these
conditions (entry 4). Tetrahydronaphthalene 9e is also
a good substrate for catalyst 10, undergoing resolution
with krel ) 39 at low temperature (entry 5). Cyclohexyl-
bearing substrate 9f undergoes kinetic resolution at a
slower rate. Nevertheless, krel ) 19 is observed at 35%
conversion after reaction at -23 °C for 6 d (entry 6).
Electron-withdrawing substituents appear to have a
deleterious effect on resolution efficiency with catalyst
10: ester-substituted substrate 9g undergoes acylation
without enantioselectivity under a variety of conditions
(entry 7). This latter result emphasizes that a fully
general catalyst remains an elusive goal.18
In summary, using a parallel enantiomer screening
assay we have found a pentapeptide catalyst that enables
nonenzymatic kinetic resolution of a number of tertiary
alcohols. Such techniques may prove useful for the rapid
identification of catalysts for the resolution of other
alcohol classes that synthetic chemists may wish to
resolve, including traditionally difficult substrates, such
as tertiary alcohols.
(14) For a review, see: (a) Spivey, A. C.; Maddaford, A.; Redgrave,
A. J . Org. Prep. Proced. Int. 2000, 32, 331. For lead references, see:
(b) Vedejs, E.; Daugulis, O. J . Am. Chem. Soc. 1999, 121, 5813. (c) Fu,
G. C. Acc. Chem. Res. 2000, 33, 412. (d) Spivey, A. C.; Fekner, T.; Spey,
S. E. J . Org. Chem. 2000, 65, 3154. (e) Sano, T.; Miyata, H.; Oriyama,
T. Enantiomer 2000, 5, 119.
(15) (a) O’Hagan, D.; Zaidi, N. A. Tetrahedron: Asymmetry 1994,
5, 1111. (b) Franssen, M. C. R.; Goetheer, E. L. V.; J ongenjan, H.;
deGroot, A. Tetrahedron Lett. 1998, 39, 8345. (c) Brackenridge, I.;
McCague, R.; Roberts, S. M.; Turner, N. J . J . Chem. Soc., Perkin Trans.
1 1993, 1093.
(16) A notable exception is the application of retroaldolase catalytic
antibodies reported by Lerner and co-workers. List, B.; Shabat, D.;
Zhong, G.; Turner, J . M.; Li, A.; Bui, T.; Anderson, J .; Lerner, R. A.;
Barbas, C. F. J . Am. Chem. Soc. 1999, 121, 7283.
Exp er im en ta l Section
Gen er a l P r oced u r es. Proton NMR spectra were recorded
on 400 or 300 NMR spectrometers. Proton chemical shifts are
reported in ppm (δ) relative to internal tetramethylsilane
(TMS, δ 0.0) or with the solvent reference relative to TMS
(17) DMAP is well-known to catalyze the acylation of tertiary
alcohols, while NMI is notably less effective. (a) Guibe-J ampel, E.;
Bram, G.; Vilkas, M. Bull. Soc. Chim. Fr. 1973, 1021. (b) Ho¨fle, G.;
Steglich, W.; Vorbru¨ggen, H. Angew. Chem., Int. Ed. Engl. 1978, 17,
569.
(18) A pentapeptide library (75 members, randomly chosen from a
theoretical library size of 8192) that contained no â-turn bias was
prepared to evaluate the role of the turn element. Each of the catalysts
from this library that was tested exhibited krel < 2.0 (attempted
resolution of 9a ). See Supporting Information for details.

Catalyst Screens via Parallel Enantiomer Analysis
J . Org. Chem., Vol. 66, No. 16, 2001 5525
employed as the internal standard (CDCl3, δ 7.26 ppm; d6-
DMSO, δ 2.50; C6D6, δ 7.16 ppm). Data are reported as
follows: chemical shift (multiplicity [singlet (s), doublet (d),
triplet (t), quartet (q), and multiplet (m)], coupling constants
[Hz], integration). Carbon NMR spectra were recorded on 400
(100 MHz) or 300 (75 MHz) spectrometers with complete
proton decoupling. Carbon chemical shifts are reported in ppm
(δ) relative to TMS with the respective solvent resonance as
the internal standard (CDCl3, δ 77.0). NMR data were collected
at ambient temperature, unless otherwise indicated. Infrared
spectra were obtained on a FT-IR spectrometer. Analytical
thin-layer chromatography (TLC) was performed using slica
gel 60 Å F254 precoated plates (0.25 mm thickness). TLC Rf
values are reported. Visualization was accomplished by ir-
radiation with a UV lamp and/or staining with KMnO4 or ceric
ammonium molybdate (CAM) solutions. Flash column chro-
matography was performed using silica gel 60 Å (32-63 µm).
Optical rotations were recorded at the sodium D line (path
length 50 mm). Elemental analyses were performed by Rob-
ertson Microlit (Madison, NJ ). High-resolution mass spectra
were obtained at the Mass Spectrometry Facilities of either
the University of Illinois (Urbana-Champaign, IL) or Boston
College (Chestnut Hill, MA). The method of ionization is given
in parentheses.
Analytical GC was performed by employing a flame ioniza-
tion detector and the column specified in the individual
experimental. Analytical and preparative reverse phase HPLC
were performed with a single wavelength UV detector (214
nm). Analytical normal phase HPLC was performed on a
chromatograph equipped with a diode array detector (214 and
254 nm). Fluorescence measurements were obtained using a
Perkin-Elmer Wallac Victor F fluorescence reader equipped
with a 380-15 nm band-pass excitation filter and a 420 nm
long-pass emission filter.
All reactions were carried out under an argon atmosphere
employing oven- and flame-dried glassware. All solvents were
distilled from appropriate drying agents prior to use. Acetic
anhydride was distilled prior to use and stored in a Schlenk
tube for no more than 1 week. Racemic trans-2-acetamidocy-
clohexanol 1 was prepared according to the method of Hawk-
ins.19 Optically pure 1 was prepared via kinetic resolution of
the racemic substrate utilizing peptidic acyl transfer catalysts
as previously reported.20 Racemic substrates 9a -f were pre-
pared via the corresponding epoxides21 according to the method
of Hawkins22 or the method of Guy.23 Substrate 9g was
prepared according to the method of Simona.24 Optically pure
9a was prepared according to the method of Sharpless.25
Stereochemical assignments/proofs of absolute stereochemistry
for 9a , 9d , and 9f are described below. Assignments for 9b,
9c, and 9e were made by analogy.
Libr a r y Syn th esis. Peptides were synthesized on the solid
support using commercially available Wang polystyrene resin
preloaded with the appropriate amino acid (Advanced Chem-
Tech). Couplings were performed using 4 equiv of amino acid
derivative, 4 equiv of HBTU, and 8 equiv of Hunig’s base in
DMF, for 3 h. Deprotections were performed using 20%
piperidine in DMF for 20 min (to minimize diketopiperazine
formation, dipeptides were deprotected using 50% piperidine
in DMF for 5 min). Peptides were cleaved from solid support
using a mixture of MeOH:DMF:NEt3 (9:1:1) for 4 days. The
peptides were characterized by electrospray mass spectrometry
and used in single enantiomer assays without further purifica-
tion. Peptides which proved selective for resolution were
purified by reverse phase HPLC techniques. Preparative
HPLC was performed using a reverse phase RP-18 X Terra
(Waters) column, eluting with 65-75% methanol in water, at
a flow rate of 6 mL/min. The purity was checked by analytical
HPLC under similar conditions, and the peptides were char-
acterized by 1H NMR and electrospray mass spectrometry.
Data for peptides 4 and 10 follow. Representative data for the
other peptides may be found in the Supporting Information.
P ep tid e 4. 1H NMR (CDCl3, 400 MHz) δ 7.56 (broad s, 1H),
7.37 (broad d, J ) 9.5 Hz, 1H), 7.29-7.20 (m, 5H), 6.92 (broad
s, 1H), 6.89 (broad d, J ) 6.2 Hz, 1H), 6.61 (broad d, J ) 9.9
Hz, 1H), 6.29 (broad s, 1H), 4.80 (dd, J ) 5.8 Hz, 13.3 Hz,
1H), 4.62 (dd, J ) 8.1 Hz, 14.9 Hz, 1H), 4.47 (dd, J ) 8.7 Hz,
14.8 Hz, 1H), 4.05 (t, J ) 6.6 Hz, 1H), 3.69 (s, 3H), 3.63 (s,
3H), 3.57 (m, 1H), 3.41 (m, 1H), 3.21 (overlapping dd and m,
J ) 4.9 Hz, 13.7 Hz, 2H), 3.08 (dd, J ) 6.6 Hz, 13.5 Hz, 1H),
2.94 (dd, J ) 5.2 Hz, 14.4 Hz, 1H), 2.07 (m, 1H), 2.01 (m, 1H),
1.87 (m, 2H), 1.76-1.62 (m, 3H), 1.48 (s, 3H), 1.42 (s, 9H),
1.35-1.12 (overlapping s and m, 7H), 0.95 (m, 2H), 0.88 (m,
4H); TLC Rf 0.26 (8% MeOH/CH2Cl2). Exact mass calcd for
[C40H59N7O8 + H]+ requires m/z 766.4503. Found 766.4502
(ES+). Analytical HPLC. Purity of peptide 4 was assayed using
a reverse phase RP-18 X Terra (Waters) column. Conditions:
isocratic elution with 60% methanol in water, at a flow rate
of 0.2 mL/min. Retention time ) 2.63 min.
P ep tid e 10. 1H NMR (CDCl3, 400 MHz) δ 7.38 (broad s,
1H), 7.30-7.16 (m, 6H), 6.84 (broad s, 1H), 6.72 (broad d, J )
8.1 Hz, 1H), 6.54 (broad d, J ) 8.8 Hz, 1H), 6.37 (broad s, 1H),
4.86 (dd, J ) 5.6 Hz, 14.0 Hz, 1H), 4.63 (m, 1H), 4.23 (m, 1H),
4.16 (t, J ) 8.6 Hz, 1H), 3.66 (s, 3H), 3.65 (overlapping s and
m, 4H), 3.29 (m, 1H), 3.12 (m, 3H), 2.96 (dd, J ) 5.7 Hz, 14.8
Hz, 1H), 2.30 (broad d, J ) 13.6 Hz, 1H), 2.09 (m, 2H), 2.01-
1.93 (m, 3H), 1.84 (m, 2H), 1.76-1.47 (m, 7H), 1.42 (s, 9H),
1.34-1.02 (m, 7H), 1.01-0.80 (m, 3H); TLC Rf 0.32 (8% MeOH/
CH2Cl2). Exact mass calcd for [C42H61N7O8 + H]+ requires m/z
792.4660. Found 792.4659 (ES+). Analytical HPLC. Purity of
peptide 10 was assayed using a reverse phase RP-18 X Terra
(Waters) column. Conditions: isocratic elution with 60%
methanol in water, at a flow rate of 0.2 mL/min. Retention
time ) 5.95 min.
Scr een in g Exp er im en ts. The optimized conditions for the
single enantiomer fluorescence assays are exemplified by the
following experimental protocol for alcohol 1. Each catalyst to
be screened was dissolved in CH2Cl2, and an aliquot (10 µL,
0.125 µmol, 2.5 mol %) was delivered to each of two vials. A
stock solution of each enantiomer of substrate 1 in 2:7 CH2-
Cl2:toluene was prepared, and an aliquot (0.45 mL, 0.0050
mmol) of the appropriate enantiomer was distributed to each
vial. An aliquot of a solution of sensor 3 and acetic anhydride
in toluene was added to each vial (40 µL, 0.00125 mmol sensor,
0.025 mmol acetic anhydride). The vials were capped and
agitated at room temperature. Aliquots (50 µL) of the reaction
mixtures were sampled into a custom-made 384-well black
Teflon plate, and fluorescence measurements were taken at
appropriate time intervals. Promising catalysts were chosen
by examining first the rate of reaction of the slower enantiomer
(giving preference to catalysts which showed reactivity in the
same range as NMI) and second the difference in rate of
reaction of the two enantiomers.
Sin gle En a n tiom er F lu or escen ce Assa ys of Rea ction
of Alcoh ol 9a . Reactions were performed in the same manner
as for alcohol 1. Each catalyst to be screened was dissolved in
CH2Cl2, and an aliquot (10 mL, 0.00075 mmol, 10 mol %) was
delivered to each of two vials. Stock solutions of each enanti-
omer of substrate 9a in 2:3 CH2Cl2:toluene were prepared, and
an aliquot (0.45 mL, 0.0075 mmol) of the appropriate enanti-
omer was distributed to each vial. An aliquot of a solution of
sensor 3 and acetic anhydride in toluene was added to each
vial (40 µL, 0.00125 mmol of sensor, 0.375 mmol of acetic
anhydride). The vials were capped and agitated at room
temperature. Fluorescence measurements were taken as with
alcohol 1.
(19) Hawkins, L. R.; Bannard, R. A. B. Can. J . Chem. 1958, 36, 220.
(20) Reference 5.
(21) Corey, E. J .; Chaykovsky, M. J . Am. Chem. Soc. 1965, 87, 1353.
(22) Reference 19.
(23) Guy, A.; Doussot, J .; Ferroud, C.; Garreau, R.; Godefroy-
Falguieres, A. Synthesis 1992, 9, 821.
(24) Simona, D.; Invidiata, F. P.; Manfredini, S.; Ferroni, R.;
Lampronti, I.; Roberti, M.; Pollini, G. P. Tetrahedron Lett. 1997, 38,
2749.
(25) (a) Sharpless, K. B.; Amberg, W.; Bennani, Y. L.; Crispino, G.
A.; Hartung, J .; J eong, K.-S.; Kwong, H.-L.; Morikawa, K.; Wang, Z.-
M.; Xu, D.; Zhang, X.-L. J . Org. Chem. 1992, 57, 2768. (b) Fleming, P.
R.; Sharpless, K. B. J . Org. Chem. 1991, 56, 2869.
Kin etic Resolu tion s. Sta n d a r d Con d ition s for Resolu -
tion of Su bstr a te 1. Alcohol (()-1 (21.0 mg, 0.133 mmol) was

5526 J . Org. Chem., Vol. 66, No. 16, 2001
J arvo et al.
dissolved in 22.2 mL of toluene. This stock solution was
distributed in 1.0 mL aliquots to reaction vessels containing
peptide catalysts (0.00015 mmol in 10 mL of CH2Cl2). A
solution of acetic anhydride in toluene (40 µL, 0.024 mmol)
was then introduced. The reactions were allowed to stir at
room temperature. Aliquots were removed, quenched with
methanol, and directly assayed by chiral GC analysis to
determine krel values as previously reported.26
Sta n d a r d Con d ition s for Resolu tion of Su bstr a te 9a .
Alcohol (()-9a (17 mg, 0.088 mmol) was dissolved in 2.3 mL
of CH2Cl2, and 3.5 mL toluene was added. This stock solution
was distributed in 1.0 mL aliquots to reaction vessels contain-
ing peptide catalysts (0.0015 mmol in 20 µL of CH2Cl2). Acetic
anhydride (70.8 µL, 0.75 mmol) and triethylamine (42 µL, 0.30
mmol) were then introduced. The reactions were allowed to
stir at room temperature. Aliquots were removed and quenched
with methanol, and solvent and amine were removed in vacuo.
The residue was dissolved in 10% 2-propanol in hexanes and
assayed by chiral HPLC analysis to determine krel values as
above.
Sta n d a r d Con d ition s for Resolu tion of Su bstr a tes
w ith P r od u ct Isola tion . Alcohol (()-9d (46 mg, 0.189 mmol)
was dissolved in 4.8 mL of CH2Cl2, and 7.6 mL of toluene was
added. A solution of peptide catalyst 10 (15 mg, 0.0189 mmol
in 250 µL of CH2Cl2) was added. The mixture was stirred and
cooled to -20 °C. Acetic anhydride (895 µL, 9.47 mmol) and
triethylamine (534 µL, 3.79 mmol) were then introduced.
Reaction progress was monitored by chiral HPLC analysis as
described in standard runs. After 82 h, methanol (5 mL) was
added and the reaction mixture was concentrated in vacuo.
The residue was purified by silica gel flash column chroma-
tography (0.25-4% MeOH/CH2Cl2) to give 9d -Ac (18 mg, 93%
ee), recovered 9d (30 mg, 35% ee), and recovered catalyst 10
(11 mg).
at 95% ee). Recovered starting material 9a from kinetic
resolution with catalyst 10: [R]D ) -38.2 (c 1.0, CH2Cl2, at
49% ee).
Su bstr a te 9b. 1H NMR (CDCl3, 400 MHz) δ 7.30 (d, J )
8.4 Hz, 2H), 7.14 (d, J ) 8.1 Hz, 2H), 6.10 (broad s, 1H), 3.80
(broad s, 1H), 3.65 (dd, J ) 13.9 Hz, 6.6 Hz, 1H), 3.39 (dd, J
) 14.1 Hz, 5.3 Hz, 1H), 2.33 (s, 3H), 1.90 (s, 3H), 1.50 (s, 3H);
13C NMR (CDCl3, 100 MHz) δ 171.5, 142.5, 136.4, 128.8, 124.7,
74.6, 51.1, 27.9, 23.1, 21.0; IR (film, cm-1) 3316, 3096, 3026,
2980, 2925, 1656; TLC Rf 0.33 (6% methanol/CH2Cl2); [R]D
-43.6 (c 1.0, CHCl3, at 88% ee). Anal. Calcd for C12H17N1O2:
C, 69.54; H, 8.27; N, 6.76. Found: C, 69.60; H, 8.13; N, 6.50.
Exact mass calcd for [C12H17N1O2 + H]+ requires m/z 208.1338.
Found 208.1337 (FAB+).
P r od u ct 9b-Ac. 1H NMR (CDCl3, 400 MHz) δ 7.17 (m, 4H),
5.83 (broad s, 1H), 3.77 (dd, J ) 14.3 Hz, 7.0 Hz, 1H), 3.63
(dd, J ) 14.3 Hz, 5.5 Hz, 1H), 2.33 (s, 3H), 2.09 (s, 3H), 1.96
(s, 3H), 1.80 (s, 3H); 13C NMR (CDCl3, 100 MHz) δ 169.7, 169.5,
138.8, 137.0, 129.0, 124.4, 83.6, 49.3, 23.4, 23.3, 22.3, 21.2; IR
(film, cm-1) 3308, 3063, 2986, 2986, 1739, 1659; TLC Rf 0.32
(6% methanol/CH2Cl2); [R]D -27.2 (c 1.0, CHCl3, at 91% ee).
Anal. Calcd for C14H19N1O3: C, 66.36; H, 7.28; N, 5.95.
Found: C, 66.16; H, 7.34; N, 5.69. Exact mass calcd for
[C14H19N1O3 + H]+ requires m/z 272.1263. Found 272.1266
(ESI+).
Assa y of En a n tiom er ic P u r ity. Enantiomers of product
9b-Ac were separated by chiral HPLC employing a Chiracel
OD column (Alltech), eluting with 5% 2-propanol/hexanes at
a flow rate of 1.0 mL/min and a temperature of 10 °C.
Retention times: 9b, Rt(R) ) 22.9 min; Rt(S) ) 28.3 min.
Retention times: 9b-Ac, Rt(S) ) 32.4 min; Rt(R) ) 37.3 min.
Product 9b-Ac was obtained with 91% ee. Recovered 9b was
produced with 83% ee (45% conversion).
1
Su bstr a te 9c. H NMR (CDCl3, 400 MHz) δ 8.1 (d, J ) 8.8
Su bstr a te 9a . 1H NMR (CDCl3, 400 MHz) δ 7.46 (d, J )
7.0 Hz, 2H), 7.36 (t, J ) 7.5 Hz, 2H), 7.27 (t, J ) 8.4 Hz, 1H),
5.70 (broad s, 1H), 3.74 (dd, J ) 14.1 Hz, 6.8 Hz, 1H), 3.40
(dd, 13.9 Hz, 5.1 Hz, 1H), 3.38 (s, 1H), 1.95 (s, 3H), 1.56 (s,
3H); 13C NMR (CDCl3, 100 MHz) δ 171.6, 145.4, 128.1, 126.8,
124.8, 74.7, 51.2, 27.9, 23.1; IR (film, cm-1) 3409, 3315, 3089,
3061, 2977, 2928, 1648; TLC Rf 0.31 (4% methanol/CH2Cl2);
[R]D -38.2 (c 1.0, CH2Cl2, at 49% ee). Anal. Calcd for
Hz, 2H), 7.65 (d, J ) 9.1 Hz, 2H), 5.75 (broad s, 1H), 4.28
(broad s, 1H), 3.73 (dd, J ) 14.3 Hz, 6.2 Hz, 1H), 3.47 (dd, J
) 14.3 Hz, 6.2 Hz, 1H), 1.95 (s, 3H), 1.58 (s, 3H); 13C NMR
(CDCl3, 100 MHz) δ 172.3, 153.1, 146.6, 126.1, 123.3, 75.3,
51.5, 28.0, 23.0; IR (film, cm-1) 3385, 3316, 3114, 3083, 2978,
2932, 1652; TLC Rf 0.143 (4% methanol/CH2Cl2); [R]D -39.6
(c 1.0, CH2Cl2, at 47% ee). Anal. Calcd for C11H14N2O4: C,
55.46; H, 5.92; N, 11.76. Found: C, 55.34; H, 5.82; N, 11.79.
Exact mass calcd for [C11H14N2O4 + H]+ requires m/z 239.1032.
Found 239.1033 (EI+).
C
11H15N1O2: C, 68.37; H, 7.82; N, 7.25. Found: C, 68.15; H,
7.93; N, 7.14. Exact mass calcd for [C11H15N1O2]+ requires m/z
193.1103. Found 193.1108 (EI+).
1
P r od u ct 9c-Ac. H NMR (CDCl3, 500 MHz) δ 8.21 (d, J )
P r od u ct 9a -Ac. 1H NMR (CDCl3, 400 MHz) δ 7.30 (m, 5H),
5.90 (broad s, 1H), 3.78 (dd, J ) 14.5 Hz, 6.8 Hz, 1H), 3.64
(dd, J ) 14.3 Hz, 5.5 Hz, 1H), 2.11 (s, 3H), 1.96 (s, 3H), 1.82
(s, 3H); 13C NMR (CDCl3, 100 MHz) δ 169.8, 169.5, 141.8,
128.4, 127.4, 124.5, 83.6, 49.3, 23.4, 22.3; IR (film, cm-1) 3390,
3301, 1738, 1659; TLC Rf 0.35 (4% methanol/CH2Cl2); [R]D
-17.6 (c 1.0, CH2Cl2, at 96% ee). Anal. Calcd for C13H17N1O3:
C, 66.36; H, 7.28; N, 5.95. Found: C, 66.16; H, 7.34; N, 5.69.
Exact mass calcd for [C13H17N1O3]+ requires m/z 235.1208.
Found 235.1206 (EI+).
8.3 Hz, 2H), 7.47 (d, J ) 8.3 Hz, 2H), 5.91 (broad s, 1H), 3.79
(dd, J ) 14.4 Hz, 6.6 Hz, 1H), 3.67 (dd, J ) 14.6 Hz, 5.8 Hz,
1H), 2.15 (s, 3H), 1.98 (s, 3H), 1.84 (s, 3H); 13C NMR (CDCl3,
125 MHz) δ 170.0, 169.6, 149.3, 147.2, 125.8, 123.7, 83.2, 48.9,
23.2 (2C), 21.9; IR (film, cm-1) 3396, 3301, 3083, 2989, 2935,
1742, 1662; TLC Rf 0.32 (4% methanol/CH2Cl2); [R]D -40.0 (c
0.58, CH2Cl2, at 96% ee). Anal. Calcd for C13H16N2O5: C, 55.71;
H, 5.75; N, 9.99. Found: C, 55.71; H, 5.68; N, 10.07. Exact
mass calcd for [C13H16N2O5 + H]+ requires m/z 281.1137.
Found 281.1137 (EI+).
Assa y of En a n tiom er ic P u r ity. Enantiomers of product
9-Ac were separated by chiral HPLC employing a Chiracel OJ
column (Alltech), eluting at a flow rate of 1 mL/min with the
following gradient: 15% 2-propanol/hexanes for 5 min, ramp
to 30% 2-propanol/hexanes over 7 min, hold until 50 min.
Retention times: 9a , Rt(S) ) 6.3 min; Rt(R) ) 7.9 min. Retention
rimes: 9a -Ac, Rt(S) ) 21.4 min; Rt(R) ) 40.3 min. Product 9a -
Ac was obtained with 96% ee; recovered 9a was produced with
49% ee (33% conversion).
P r oof of Absolu te Ster eoch em istr y for 9a . Recovered
starting material was compared to authentic (R)-9a prepared
according to the method of Sharpless.27 Asymmetric dihy-
droxylation of 2-phenylpropene25a was followed by conversion
to the azido alcohol.25b Hydrogenation and acetylation provided
(R)-9a that was found to exhibit [R]D ) -82.8 (c 1.0, CH2Cl2
Assa y of En a n tiom er ic P u r ity. Enantiomers of starting
material 9c were separated by chiral HPLC employing a
Chiracel OB-H column (Alltech), eluting with 10% 2-propanol/
hexanes at a flow rate of 1.0 mL/min. Retention times: 9c,
Rt(S) ) 33.9 min; Rt(R) ) 39.8 min. Enantiomers of product 9c-
Ac were separated by chiral HPLC employing a Chiracel AD
column (Alltech), eluting with 9% 2-propanol/hexanes at a flow
rate of 1.0 mL/min. Retention times: 9c-Ac, Rt(R) ) 23.9 min;
Rt(S) ) 25.9 min. Product 9c-Ac was obtained with 96% ee.
Recovered 9c was produced with 47% ee (33% conversion).
1
Su bstr a te 9d . H NMR (CDCl3, 400 MHz) δ 7.97 (s, 1H),
7.85-7.82 (m, 3H), 7.52-7.46 (m, 3H), 5.76 (broad s, 1H), 3.83
(dd, J ) 14.1 Hz, 6.8 Hz, 1H), 3.72 (broad s, 1H), 3.50 (d, J )
14.1 Hz, 5.3 Hz, 1H), 1.90 (s, 3H), 1.63 (s, 3H); 13C NMR
(CDCl3, 100 MHz) δ 171.7, 142.8, 133.0, 132.3, 128.1, 128.0,
127.4, 126.1, 125.8, 123.7, 123.2, 75.2, 51.4, 28.2, 23.2; IR (film,
cm-1) 3317, 3061, 2976, 2928, 1656; TLC Rf 0.16 (4% methanol/
CH2Cl2); [R]D +3.4 (c 1.0, EtOH, at 35% ee). Anal. Calcd for
(26) (a) S values were calculated according to the method of Kagan.
See: Kagan, H. B.; Fiaud, J . C. Top. Stereochem. 1988, 18, 249. (b)
See also: ref 5.
(27) See ref 25.
C15H17N1O2: C, 74.05; H, 7.04; N, 5.76. Found: C, 73.86; H,

Catalyst Screens via Parallel Enantiomer Analysis
J . Org. Chem., Vol. 66, No. 16, 2001 5527
1
6.79; N, 5.76. Exact mass calcd for [C15H17N1O2 + Na]+
requires m/z 266.1157. Found 266.1150 (ESI+).
P r od u ct 9f-Ac. H NMR (CDCl3, 400 MHz) δ 6.56 (broad
s, 1H), 3.75 (dd, J ) 14.8 Hz, 7.1 Hz, 1H), 3.45 (dd, J ) 14.9
Hz, 4.9 Hz, 1H), 2.04 (s, 3H), 2.01, (s, 3H), 1.95 (m, 1H), 1.78
(broad m, 2H), 1.69 (broad m, 3H), 1.29 (s, 3H), 1.25-1.00
(broad m, 5H); 13C NMR (CDCl3, 100 MHz) δ 171.2, 169.8, 87.6,
45.0, 44.1, 27.5, 27.0, 26.6, 26.5 (2C), 23.6, 22.4, 19.5; IR (film,
cm-1) 3295, 3090, 2929, 2856, 1727, 1654; TLC Rf 0.15 (4%
MeOH/CH2Cl2); [R]D +9.2 (c 1.0, CHCl3, at 88% ee). Anal. Calcd
for C13H23N1O3: C, 64.70; H, 9.61; N, 5.80. Found: C, 64.68;
H, 9.45; N, 5.56. Exact mass calcd for [C13H23N1O3 + Na]+
requires m/z 264.1576. Found 264.1576 (ESI+).
Assa y of En a n tiom er ic P u r ity. Enantiomers of product
9f-Ac were separated by chiral GC employing a 40 m CHIRAL-
DEX B-DM column (Advanced Separation Technologies, Inc.)
connected in-line to a 30 m achiral precolumn (HP-5, Hewlett-
Packard), with a He pressure of 40 psi at the following
temperature gradient: 150 °C for 25 min, followed by a 2 min
ramp to 120 °C for 45 min followed by a 1 min ramp to 135 °C
for 15 min, followed by an additional 1 min ramp to 145 °C
for 45 min Retention times: 9e, Rt(S) ) 105.0 min; Rt(R) ) 109.4
min. Retention times: 9f-Ac, Rt(R) ) 76.6 min; Rt(S) ) 78.3 min.
Product 9f-Ac was obtained with 88% ee. Recovered 9f was
produced with 48% ee (35% conversion).
P r od u ct 9d -Ac. 1H NMR (CDCl3, 400 MHz) δ 7.85-7.80
(m, 3H), 7.75 (s, 1H), 7.51-7.45 (m, 2H), 7.41 (d, J ) 8.8 Hz,
1H), 5.94 (br s, 1H), 3.87 (dd, J ) 14.3 Hz, 6.6 Hz, 1H), 3.77
(dd, J ) 14.3 Hz, 5.5 Hz, 1H), 2.16 (s, 3H), 1.96 (s, 3H), 1.91
(s, 3H); 13C NMR (CDCl3, 100 MHz) δ 169.9, 169.5, 139.2,
132.8, 132.4, 128.2, 128.0, 127.3, 126.2, 126.0, 123.6, 122.4,
83.7, 49.1, 23.4, 23.3, 22.3; IR (film, cm-1) 3302, 3060, 2986,
2935, 1736, 1655; TLC Rf 0.28 (4% methanol/CH2Cl2); [R]D
-15.3 (c 0.67, EtOH, at 86% ee). Anal. Calcd for C17H19N1O3:
C, 71.56; H, 6.71; N, 4.91. Found: C, 71.17; H, 6.43; N, 4.71.
Exact mass calcd for [C17H19N1O3 + Na]+ requires m/z 308.1263.
Found 308.1258 (ESI+).
Assa y of En a n tiom er ic P u r ity. Enantiomers of product
9d -Ac were separated by chiral HPLC employing a Chiracel
OJ column (Alltech), eluting at a flow rate of 1.0 mL/min with
the following gradient: 12% 2-propanol/hexanes for 23 min,
ramp to 20% 2-propanol/hexanes over 2 min, hold until 105
min. Retention times: 9d , Rt(S) ) 15.3 min; Rt(R) ) 17.5 min.
Retention times: 9d -Ac, Rt(S) ) 34.0 min; Rt(R) ) 90.6 min.
Product 9d -Ac was obtained with 35% ee. Recovered 9d was
produced with 86% ee (29% conversion).
P r oof of Absolu t e St er eoch em ist r y for 9d : recovered
starting material as compared to authentic (R)-9d prepared
in analogy to the method employed for substrate 9a . Authentic
(R)-9d was found to exhibit [R]D +10.3 (c 1.0, EtOH, at 97%
ee). Recovered starting material 9d from kinetic resolution
with catalyst 10: [R]D ) +3.4 (c 1.0, EtOH, at 35% ee).
Su bstr a te 9e. 1H NMR (CDCl3, 400 MHz) δ 7.14 (d, J )
9.5 Hz, 2H), 7.05 (d, J ) 7.7 Hz, 1H), 5.78 (broad s, 1H), 3.74
(dd, J ) 14.1 Hz, 7.1 Hz, 1H), 3.36 (dd, J ) 13.9 Hz, 5.1 Hz,
1H), 3.17 (s, 1H), 2.76 (broad m, 4H), 1.96, (s, 3H), 1.80 (broad
s, 4H), 1.52 (s, 3H); 13C NMR (CDCl3, 100 MHz) δ 171.4, 142.5,
136.9, 135.7, 128.9, 125.4, 121.8, 74.6, 51.5, 29.7, 29.1, 28.0,
23.3 (2C), 23.2; IR (film, cm-1) 3314, 3094, 2976, 2928, 2857,
1650; TLC Rf 0.26 (6% MeOH/CH2Cl2); [R]D -29.0 (c 1.0 CHCl3,
at 40% ee). Anal. Calcd for C15H21N1O2: C, 72.84; H, 8.56; N,
5.66. Found: C, 72.61; H, 8.23; N, 5.45. Exact mass calcd for
[C15H21N1O2 + Na]+ requires m/z 270.1470. Found 270.1465
(ESI+).
P r oof of Ab solu t e St er eoch em ist r y for 9f. Recovered
starting material was compared to authentic (S)-9f prepared
according to the method of J acobsen28 that was found to
exhibit: [R]D ) -3.2 (c 2.8, CHCl3, at >99% ee). Recovered
starting material 9f from the kinetic resolution with catalyst
10: [R]D +1.6 (c 2.5, CHCl3, at 48% ee).
Su bstr a te 9g. 1H NMR (CDCl3, 400 MHz) δ 7.60 (d, J )
8.1 Hz, 2H), 7.36 (m, 3H), 5.92 (broad s, 1H), 4.50 (s, 1H), 4.22
(dd, J ) 13.9 Hz, 7.0 Hz, 1H), 3.79 (s, 3H), 3.62 (dd, J ) 13.9
Hz, 4.8 Hz, 1H), 1.97 (s, 3H); 13C NMR (CDCl3, 100 MHz) δ
173.6, 171.0, 138.7, 128.2, 125.2, 78.7, 53.3, 47.6, 23.0; IR (film,
cm-1) 3308, 3066, 2951, 1734, 1655; TLC Rf 0.06 (2% MeOH/
CH2Cl2). Anal. Calcd for C12H15N1O4: C, 60.75; H, 6.37; N, 5.90.
Found: C, 60.69; H, 6.23; N, 5.80. Exact mass calcd for
[C12H15N1O4 + Na]+ requires m/z 260.0899. Found 260.0898
(ESI+).
P r od u ct 9g-Ac. 1H NMR (CDCl3, 400 MHz) δ 7.45 (m, 2H),
7.37 (m, 3H), 5.58 (broad s, 1H), 4.41 (dd, J ) 14.6 Hz, 7.3 Hz,
1H), 3.94 (dd, J ) 14.6 Hz, 5.5 Hz, 1H), 3.71 (s, 3H), 2.21 (s,
3H), 1.82 (s, 3H); 13C NMR (CDCl3, 100 MHz) δ 170.0, 169.8,
169.7, 135.6, 128.6, 128.6, 124.9, 82.4, 52.8, 44.1, 23.2, 21.2;
IR (film, cm-1) 3393, 3298, 3071, 3028, 2956, 1742, 1659; TLC
Rf 0.14 (2% MeOH/CH2Cl2). Anal. Calcd for C14H17N1O5: C,
60.21; H, 6.14; N, 5.02. Found: C, 60.01; H, 5.90; N, 4.87. Exact
mass calcd for [C14H17N1O5 + Na]+ requires m/z 302.1004.
Found 302.1004. (ESI+).
Assa y of En a n tiom er ic P u r ity. Enantiomers of product
9g-Ac were separated by chiral HPLC employing a Chiracel
AD column (Alltech), eluting with 4% 2-propanol/hexanes at
a flow rate of 0.8 mL/min. Retention times: 9g, Rt ) 68.6 min;
Rt ) 78.0 min. Retention times: 9g-Ac, Rt ) 52.7 min; Rt )
62.6 min.
P r od u ct 9e-Ac. 1H NMR (CDCl3, 400 MHz) δ 7.00 (m, 3H),
5.87 (broad s, 1H), 3.77 (dd, J ) 14.3 Hz, 7.0 Hz, 1H), 3.60
(dd, J ) 14.3 Hz, 5.5 Hz, 1H), 2.74 (broad m, 4H), 2.10 (s, 3H),
1.98 (s, 3H), 1.78 (broad s, 7H); 13C NMR (CDCl3, 100 MHz) δ
169.8, 169.6, 138.8, 137.1, 136.4, 129.1, 125.2, 121.6, 83.6, 49.4,
29.7, 29.1, 23.5, 23.4, 23.2 (2C), 22.4; IR (film, cm-1) 3305, 3081,
2986, 2928, 2859, 1736, 1656; TLC Rf 0.34 (6% MeOH/CH2-
Cl2); [R]D -25.0 (c 1.0, CHCl3, at 89% ee). Anal. Calcd for
C
17H23N1O3: C, 70.56; H, 8.01; N, 4.84. Found: C, 70.48; H,
7.95; N, 4.92. Exact mass calcd for [C17H23N1O3 + Na]+
requires m/z 312.1576. Found 312.1573 (ESI+).
Assa y of En a n tiom er ic P u r ity. Enantiomers of product
9e-Ac were separated by chiral HPLC employing a Chiracel
OJ column (Alltech), eluting at a flow rate of 1 mL/min with
the following gradient: 3% 2-propanol/hexanes for 54 min,
ramp to 10% 2-propanol/hexanes over 1.5 min, hold until 70
min. Retention times: 9e, Rt(R) ) 29.0 min; Rt(S) ) 31.5 min.
Retention times: 9e-Ac, Rt(S) ) 52.3 min; Rt(R) ) 63.0 min.
Product 9e-Ac was obtained with 89% ee. Recovered 9e was
produced with 40% ee (30% conversion).
Ack n ow led gm en t. This research is supported by
the NSF (CHE-9874963). We also thank the NIH,
DuPont, Eli Lilly, Glaxo-Wellcome, and Merck for
research support. S.J .M. is a Fellow of the Alfred P.
Sloan Foundation, a Cottrell Scholar of Research Cor-
poration, and a Camille Dreyfus Teacher-Scholar.
1
Su bstr a te 9f. H NMR (CDCl3, 400 MHz) δ 6.21 (broad s,
1H); 3.33 (dd, J ) 13.9 Hz, 6.6 Hz, 1H), 3.24 (dd, J ) 13.6 Hz,
5.1 Hz, 1H), 2.69 (s, 1H), 2.03 (s, 3H), 1.87-1.67 (broad m,
5H), 1.36 (m, 1H), 1.25-0.96 (broad m, 5H), 1.08 (s, 3H); 13C
NMR (CDCl3, 100 MHz) δ 170.9, 74.6, 47.7, 46.5, 27.9, 26.8
(2C), 26.7, 26.5, 23.4, 21.6; IR (film, cm-1) 3308, 3093, 2973,
2925, 2852, 1650; TLC Rf 0.08 (4% MeOH/CH2Cl2); [R]D +1.6
(c 2.5, CHCl3, at 48% ee). Anal. Calcd for C11H21N1O2: C, 66.29;
H, 10.62; N, 7.03. Found: C, 66.16; H, 10.38; N, 6.91. Exact
mass calcd for [C11H21N1O2 + Na]+ requires m/z 222.1470.
Found 222.1465 (ESI+).
Su p p or tin g In for m a tion Ava ila ble: A summary of li-
brary members and their identification. This material is
available free of charge via the Internet at http://pubs.acs.org.
J O015803Z
(28) Lebel, H.; J acobsen, E. N. Tetrahedron Lett. 1999, 40, 7303.