Rearrangement of α-amino cyclopropanone hydrate: A novel route to labeled amino acids

Full text of DOI:10.1021/jo001126h

J . Org. Chem. 2001, 66, 305-308
305
Sch em e 1
Sch em e 2
Rea r r a n gem en t of r-Am in o
Cyclop r op a n on e Hyd r a te: A Novel Rou te
to La beled Am in o Acid s
Franc¸ois-Xavier Felpin,† Eric Doris,*† Alain Wagner,‡
Alain Valleix,† Bernard Rousseau,† and
Charles Mioskowski†,‡
CEA/ Saclay, Service des Mole´cules Marque´es, Baˆt. 547,
De´partement de Biologie Cellulaire et Mole´culaire,
91191 Gif sur Yvette Cedex, France, and Laboratoire de
Synthe`se Bio-Organique associe´ au CNRS, Universite´ Louis
Pasteur, Faculte´ de Pharmacie, 74 route du Rhin,
67401 Illkirch, France
eric.doris@cea.fr
Received J uly 25, 2000
Sch em e 3
In tr od u ction
Amino acids specifically labeled with stable isotopes
are valuable tools for the investigation of proteins at the
atomic level. Indeed, the combination of stable isotope
labeling and multidimensional NMR spectroscopy is a
highly efficient method for the structural study of pro-
teins and peptides in solution.1 Furthermore, labeled
amino acids are of prime importance in the elucidation
of many enzyme mechanisms.2
The classical methods for the synthesis of deuterium-
labeled amino acids involve either isotopic exchange3 or
deuteriogenation of a suitable precursor that incorporates
a double bond.4 Herein, we report a new route to
regioselectivelly deuterated amino acids. Our approach
derives from a 1932 observation by Lipp et al.5 who
reported the expeditious fragmentation of cyclopropanone
hydrate into propanoic acid (Scheme 1).
In principle, an R-amino cyclopropanone hydrate such
as 1 should display the same reactivity and, hence,
rearrange either to the corresponding R-amino acid 2a
(alanine) or â-amino acid 2b (Scheme 2). Furthermore,
as the ring opening of the cyclopropane presumably
occurs with internal proton transfer, the incorporation
of a deuterium label on the hydrate moiety should afford
labeling of the resulting amino acid.
undertaken (Scheme 3). Our syntheses started from the
appropriate R-bromo aldehyde6 that was protected as a
1,2-benzenedimethyloxy acetal. The choice of 1,2-ben-
zenedimethyloxy acetal as hydrate protecting group was
governed by its facile removal through catalytic reduc-
tion. In a deuterium atmosphere, this should permit the
incorporation of a deuterium label on both oxygen atoms
and thereby install the labeling source for the ensuing
oxygen to carbon isotope transfer. Bromine â-elimina-
tion,7 followed by catalytic cyclopropanation8 of the
resulting ketene acetal 4a -d with diazoacetonitrile af-
forded cyclopropyl nitrile 5a -d . The nitrile group was
hydrolyzed with KOH in t-BuOH,9 and the resulting
amide 6a -d was converted to the corresponding cyclo-
propyl N-methyl carbamate 7a -d through DIB-mediated
Hofmann rearrangement.10
Resu lts a n d Discu ssion
To corroborate this hypothesis, the preparation of four
different potential precursors (7a -d ) of amino acids was
* To whom correspondence should be addressed.
† CEA/Saclay.
‡ Universite´ Louis Pasteur.
(1) (a) Kessler, H.; Griesinger, C.; Wagner, K. J . Am. Chem. Soc.
1987, 109, 6927-6933. (b) Nietlispach, D.; Clowes, R. T.; Broadhurst,
R. W.; Ito, Y.; Keeler, J .; Kelly, M.; Ashurst, J .; Oschkinat, H.; Domaille,
P. J .; Laue, E. D. J . Am. Chem. Soc. 1996, 118, 407-415. (c) Gardner,
K. H.; Kay, L. E. J . Am. Chem. Soc. 1997, 119, 7599-7600.
(2) (a) Battersby, A. R.; Nicoletti, M.; Staunton, J .; Vleggaar, R. J .
Chem. Soc., Perkin Trans. 1 1980, 43-51. (b) Baldwin, J . E.; Adlington,
R. M.; Ting, H. H.; Arigoni, D.; Graf, P.; Martinoni, B. Tetrahedron
1985, 41, 3339-3343. (c) Furuta, T.; Takahashi, H.; Kasuya, Y. J . Am.
Chem. Soc. 1990, 112, 3633-3636.
The four different precursors were subjected to deu-
teriogenolysis in anhydrous EtOAc in the presence of Pd/
C. The results are summarized in the Table 1. As
expected, the rearrangement of substrates 7a ,b afforded
the corresponding R-amino acids (â-deuterated alanine
(3) (a) Fujihara, H.; Schowen, R. L. J . Org. Chem. 1984, 49, 2819-
2820. (b) Faleev, N. G.; Ruvinov, S. B.; Saporovskaya, M. B.; Belikov,
V. M.; Zakomyrdina, L. N.; Sakharova, I. S.; Torchinsky, Y. M.
Tetrahedron Lett. 1990, 31, 7051-7054. (c) Rose, J . E.; Leeson, P. D.;
Gani, D. J . Chem. Soc., Perkin Trans. 1 1995, 157-166. (d) Ross, F.
C.; Botting, N. P.; Leeson, P. D. Tetrahedron 1997, 53, 15761-15770.
(4) Oba, M.; Ueno, R.; Fukuoka, M.; Kainosho, M.; Nishiyama, K.
J . Chem. Soc., Perkin Trans. 1 1995, 1603-1610.
(6) Meakins, G. D.; Musk, S. R. R.; Robertson, C. A.; Woodhouse, L.
S. J . Chem. Soc., Perkin Trans. 1 1989, 643-648.
(7) Grewe, R.; Struve, A. Chem. Ber. 1963, 96, 2819-2821
(8) Dowd, P.; Kaufman, C.; Paik, Y. H. Tetrahedron Lett. 1985, 26,
2283-2286.
(9) Hall, J . H.; Gisler, M. J . Org. Chem. 1976, 41, 3769-3770.
(10) Moriarty, R. M.; Chany, C. J .; Vaid, R. K.; Prakash, O.;
Tuladhar, S. M. J . Org. Chem. 1993, 58, 2478-2482.
(5) Lipp, P.; Buchkremer, J .; Seeles, H. J ustus Liebigs Ann. Chem.
1932, 499, 1-25.
10.1021/jo001126h CCC: $20.00 © 2001 American Chemical Society
Published on Web 12/09/2000

306 J . Org. Chem., Vol. 66, No. 1, 2001
Notes
Ta ble 1. Deu ter iogen olysis of Am in o Acid P r ecu r sor s
Sch em e 5
group. The hydrate oxygen atoms then act as electron
donors and the cyclopropane carbon atoms as electron
acceptors. The relative stability of the indicated partial
negative charge could be one of the factors that directs
the cyclopropane rearrangement. For example, R sub-
stituents on substrate 7b (R1 ) H and R2 ) Ph) promote
stabilization of the partial negative charge at the adjacent
carbon atom through the electron-withdrawing effect of
the phenyl ring. It is also conceivable that, for 7a (R1 )
H and R2 ) H), the formation of a partial negative charge
takes place preferentially on the unsubstituted methyl-
ene carbon. However, the rearrangement of 7c,d (R1 )
alkyl or H, R2 ) alkyl) employs pathway B, where the
electron-rich alkyl groups center the incipient negative
species on carbon adjacent to nitrogen. Subsequent ring
opening generates a σ-Pd complex11 that undergoes either
reductive- (a) or â-elimination (b or c) followed by in situ
reduction by D2 gas. In the case of R-amino acids,
reductive elimination (a) appears to be the only active
process (no labeling was detected other than on the side
chain). However, for â-amino acids12 â-elimination (b and/
or c) is probably also operative. Indeed, 8d was labeled
in two positions, namely on the methylene carbon atom
adjacent to nitrogen (H/D: 0.26) and on the methine
carbon atom adjacent to the carboxylic group (H/D: 0.87).
The same strategy was applied with success to the
synthesis of optically enriched D-phenylalanine 12 (Scheme
5) using, as the key step, an asymmetric Rh2(5S-MEPY)4
mediated cyclopropanation.13 This afforded the chiral
cyclopropane 9 with a cis/ trans ratio of 90/10. The cis
isomer (66% ee) was isolated by column chromatography
and converted into the corresponding amide 10. It should
be noted that the center adjacent to the nitrile moiety
was fully inverted during the basic hydration step,
leading to trans cyclopropane 10 without any loss of
optical purity. The amide group was then rearranged
stereospecifically14 to carbamate 11 using DIB. Finally,
a
Yields obtained after treatment of the crude reaction mixture
with diazomethane. The amino acid was isolated as its methyl
ester. Isotopic enrichments were determined by mass spectrom-
etry.
b
Sch em e 4
8a and phenylalanine 8b, respectively) in high yield and
high isotopic purity. A 5 to 10% increase in isotopic
enrichment was observed with deuteriogenolysis in meth-
anol-d (>99% D). Surprisingly, substrates 7c,d exclu-
sively furnished the labeled â-amino acid. In all cases
the rearrangement is highly regioselective. The difference
in reactivity between amino acid precursors 7a ,b and
7c,d may be rationalized by two pathways, A and B
(Scheme 4), in which palladium plays a key role in the
rearrangement of the cyclopropanone hydrate. Indeed,
it has recently been reported that Pd/C catalyzes the ring
opening of cyclopropanols.11 On the basis of this report,
we suggest that, in the first step, a palladium alkoxide
is formed by oxidative addition of Pd(0) to the hydrate
(11) Okumoto, H.; J innai, T.; Shimizu, H.; Harada, Y.; Mishima, H.;
Suzuki, A. Synlett 2000, 629-630
(12) For a recent review on the preparation of â-amino acids, see:
Abele, S.; Seebach, D. Eur. J . Org. Chem. 2000, 1-15.
(13) (a) Doyle, M. P.; Pieters, R. J .; Martin, S. F.; Austin, R. E.;
Oalmann, C. J .; Mu¨ller, P. J . Am. Chem. Soc. 1991, 113, 1423-1424.
(b) Doyle, M. P.; Winchester, W. R.; Hoorn, J . A. A.; Lynch, V.;
Simonsen, S. H.; Ghosh, R. J . Am. Chem. Soc. 1993, 115, 9968-9978.
(c) Doyle, M. P.; Austin, R. E.; Bailey, A. S.; Dwyer, M. P.; Dyatkin, A.
B.; Kalinin, A. V.; Kwan, M. M. Y.; Liras, S.; Oalmann, C. J .; Pieters,
R. J .; Protopopova, M. N.; Raab, C. E.; Roos, G. H. P.; Zhou, Q. L.;
Martin, S. F. J . Am. Chem. Soc. 1995, 117, 5763-5775.

Notes
J . Org. Chem., Vol. 66, No. 1, 2001 307
was pure enough and was used without further purification.
Ketene acetal 4a 17 was obtained as a white solid (4.80 g, 99%
yield). 1H NMR (CDCl3) δ 3.76 (s, 2H), 5.09 (s, 4H), 7.10-7.28
(m, 4H). 13C NMR (CDCl3) δ 69.4, 72.0, 126.1, 127.4, 135.8, 164.2.
MS (CI/NH3): 163 (M + 1, 100).
7-Be n zylid e n e -5,9-d ih yd r o-6,8-d ioxa -b e n zocycloh e p -
ten e 4b (white needles, 0.89 g, 99% yield): 1H NMR (CDCl3) δ
5.20 (s, 2H), 5.28 (s, 3H), 7.13-7.53 (m, 9H). 13C NMR (CDCl3)
δ 71.3, 73.4, 88.4, 125.0, 126.0, 126.6, 127.3, 127.4, 127.7, 128.2,
135.4, 136.0, 159.4. MS (CI/NH3): 239 (M + 1, 100). IR (KBr):
1677 (CdC).
7-Isop r op ylid en e-5,9-d ih yd r o-6,8-d ioxa -ben zocycloh ep -
ten e 4c (white powder, 1.34 g, 95% yield): 1H NMR (CDCl3) δ
1.69 (s, 6H), 5.06 (s, 4H), 7.10-7.13 (m, 2H), 7.24-7.27 (m, 2H).
13C NMR (CDCl3) δ 16.2, 71.7, 87.7, 126.2, 127.2, 136.7, 153.2.
MS (CI/NH3): 191 (M + 1, 100). IR (KBr): 1720 (CdC).
7-P r op ylid e n e -5,9-d ih yd r o-6,8-d ioxa -b e n zocycloh e p -
ten e 4d (pale yellow oil, 1.81 g, 89% yield): 1H NMR (CDCl3) δ
1.02 (t, J ) 7.3 Hz, 3H), 2.08 (m, 2H), 4.19 (t, J ) 7.3 Hz, 1H),
5.06 (s, 2H), 5.09 (s, 2H), 7.09-7.26 (m, 4H). 13C NMR (CDCl3)
δ 15.1, 17.8, 71.4, 72.6, 87.3, 126.0, 126.3, 127.2, 127.3, 136.2,
136.4, 158.0. MS (CI/NH3): 191 (M + 1, 100). IR (KBr): 1699
(CdC).
palladium-catalyzed hydrogenolysis of 11 led to N-methyl
carbamate D-phenylalanine methyl ester 12 in 91% yield
with an enantiomeric excess15 of 66%. The utilization of
hydrogen instead of deuterium for the benzyl deprotec-
tion step was dictated by the necessity to avoid the
introduction of a second chiral center (on the side chain)
that would have complicated the assignment of absolute
stereochemistry to the amino acid.
In conclusion, we have shown that the rearrangement
of R-amino cyclopropanone hydrates provides an easy
route to amino acid derivatives. The method was ex-
tended to the synthesis of optically enriched D-phenyl-
alanine derivative (66% ee). The approach developed here
permits the incorporation of isotopic labeling and is
particularly well adapted for the preparation of radioac-
tively labeled amino acids using, for example, tritium gas.
Exp er im en ta l Section
2
Gen er a l Meth od s. 1H NMR, 13C NMR, and H NMR spectra
were recorded at 300, 75, and 46 MHz using residual CHCl3 (7.25
ppm), CDCl3 (77 ppm), and CDCl3 (7.25 ppm) as internal
standard, respectively. Flash column chromatography was per-
formed on Merck silica gel (60 Å, 230-400 mesh). All reactions
were performed under Ar in a flame-dried flask using anhydrous
solvents. HRMS were recorded at the “Centre Re´gional de
Mesures Physiques de l′Ouest”. Reagents were purchased from
Aldrich Chemical Co.
Syn th esis of Cyclop r op yl Nitr iles 5a -d . A typical experi-
mental procedure is given for the synthesis of 5b. To a refluxing
solution of ketene acetal 4b (0.5 g, 2.1 mmol, 1 equiv) and Rh2-
(OAc)4 (1 mol %) in 5 mL of CH2Cl2 was added over a period of
8 h, via a seringe pump, diazoacetonitrile16 (25 mL of a 0.1 M
soln in CH2Cl2, 1.2 equiv). The solution was cooled to room
temperature and filtered over Celite, and the solvent was
removed under reduced pressure. Chromatography over silica
(hexane:EtOAc, 9:1) allowed the separation of each diastereomer
(ratio: 1/1) which were obtained in a combined 55% yield (0.320
g, white powder). Cis cyclopropyl nitrile 5b (9): Rf 0.3 (hexane:
Syn th esis of Aceta ls 3a -d . 7-Bromomethyl-5,9-dihydro-6,8-
dioxa-benzocycloheptene 3a was synthesized according to lit-
erature procedures.7 For 3b-d , a typical experimental procedure
is given for the synthesis of 7-(1-bromo-1-phenylmethyl)-5,9-
dihydro-6,8-dioxa-benzocycloheptene 3b. To a solution of 2-bromo-
2-phenylacetaldehyde6 (1.8 g, 9 mmol, 1 equiv) in 70 mL of
toluene were added 1,2-benzenedimethanol (1.37 g, 1.1 equiv)
and p-TsOH (0.2 g, cat). The mixture was heated to reflux for 3
h in a Dean-Stark apparatus, cooled to room temperature, and
diluted with 50 mL of Et2O. The organic layer was washed with
10% NaHCO3, and the aqueous layer was extracted twice with
Et2O. The combined organic layers were dried over MgSO4,
filtered, and evaporated under reduced pressure. Acetal 3b was
obtained pure as white crystals after recrystallization from Et2O
1
EtOAc, 8:2). H NMR (CDCl3) δ 2.48 (d, J ) 10.3 Hz, 1H), 2.99
(d, J ) 10.3 Hz, 1H), 4.95-5.18 (m, 4H), 7.17-7.52 (m, 9H). 13
C
NMR (CDCl3) δ 18.0, 34.7, 71.0, 71.3, 94.6, 115.6, 127.1, 127.3,
127.8, 128.5, 129.2, 131.3, 137.0. Trans cyclopropyl nitrile 5b:
1
Rf 0.4 (hexane:EtOAc, 8:2). H NMR (CDCl3) δ 2.27 (d, J ) 6.7
Hz, 1H), 3.13 (d, J ) 6.7 Hz, 1H), 4.80 (m, 2H), 5.08 (d, J ) 14.4
Hz, 1H), 5.26 (d, J ) 14.4 Hz, 1H), 7.10-7.42 (m, 9H). 13C NMR
(CDCl3) δ 17.8, 37.4, 71.2, 71.3, 95.0, 117.3, 127.1, 127.3, 127.7,
127.9, 128.6, 132.5, 137.0, 137.2.
Cyclop r op yl Nitr ile 5a . Addition of diazoacetonitrile over
a period of 5 h at room temperature, 5a was obtained in 66%
yield (3.84 g, white powder). Rf 0.2 (hexane:EtOAc, 9:1). 1H NMR
(CDCl3) δ 1.76 (m, 2H), 2.04 (dd, J ) 7.0 and 9.8 Hz, 1H), 4.95-
5.28 (m, 4H), 7.26-7.37 (m, 4H). 13C NMR (CDCl3) δ 11.3, 21.0,
71.5, 93.4, 117.9, 127.3, 127.4, 127.8, 127.9, 137.1, 137.3.
Cyclop r op yl Nitr ile 5c. Addition of diazoacetonitrile over
a period of 3 h under reflux, 5c was obtained in 78% yield (0.94
1
(2.30 g, 80% yield). H NMR (CDCl3) δ 4.78-5.06 (m, 5H), 5.32
(d, J ) 6.1 Hz, 1H), 7.19-7.49 (m, 9H). 13C NMR (CDCl3) δ 53.1,
71.7, 107.7, 127.3, 127.5, 127.6, 128.5, 128.7, 138.2, 138.3.
7-Br om om et h yl-5,9-d ih yd r o-6,8-d ioxa -b en zocycloh ep -
ten e 3a (white crystals, 7.31 g, 90% yield): 1H NMR (CDCl3) δ
3.48 (d, J ) 5.1 Hz, 2H), 4.95 (s, 4H), 5.15 (t, J ) 5.1 Hz, 1H),
7.19-7.28 (m, 4H). 13C NMR (CDCl3) δ 31.4, 71.7, 105.7, 127.3,
127.6, 138.3.
1
g, white powder). Rf 0.3 (hexane:EtOAc, 9:1). H NMR (CDCl3)
δ 1.33 (s, 3H), 1.43 (s, 3H), 1.59 (s, 1H), 4.87 (d, J ) 14 Hz, 1H),
4.96 (d, J ) 14.2 Hz, 1H), 5.05 (d, J ) 14 Hz, 1H), 5.21 (d, J )
14.2 Hz, 1H), 7.17-7.30 (m, 4H). 13C NMR (CDCl3) δ 16.9, 19.7,
21.0, 31.1, 70.6, 70.8, 97.7, 116.8, 126.8, 127.0, 127.4, 127.5,
137.0, 137.3.
7-(1-Br om o-1-m eth yleth yl)-5,9-d ih yd r o-6,8-d ioxa -ben zo-
cycloh ep ten e 3c (white crystals, 3.90 g, 85% yield): 1H NMR
(CDCl3) δ 1.78 (s, 6H), 4.82 (s, 1H), 4.98 (s, 4H), 7.22-7.29 (m,
4H). 13C NMR (CDCl3) δ 29.0, 64.5, 73.7, 112.5, 127.8, 139.0.
7-(1-Br om opr opyl)-5,9-dih ydr o-6,8-dioxa-ben zocycloh ep-
ten e 3d (white crystals, 3.50 g, 78% yield): 1H NMR (CDCl3) δ
1.10 (t, J ) 7.3 Hz, 3H), 1.80-1.93 (m, 1H), 2.02-2.15 (m, 1H),
3.97-4.04 (m, 1H), 4.94-5.02 (m, 5H), 7.19-7.27 (m, 4H). 13C
NMR (CDCl3) δ 11.8, 26.5, 56.9, 72.1, 72.3, 108.3, 126.1, 127.4,
127.6, 129.0, 138.5, 138.6.
Syn th esis of Keten e Aceta ls 4a -d . A typical experimental
procedure is given for the preparation of 7-methylene-5,9-
dihydro-6,8-dioxa-benzocycloheptene 4a . To a solution of 7-bro-
momethyl-5,9-dihydro-6,8-dioxa-benzocycloheptene 3a (7.20 g,
29,6 mmol, 1 equiv) in 150 mL of anhydrous THF was added
portionwise at 0 °C t-BuOK (3.65 g, 1.1 equiv). The mixture was
heated to reflux for 1 h, cooled to room temperature, and diluted
with 50 mL of Et2O. The solution was filtered over Celite, and
the solvents were removed under reduced pressure. The crude
Cyclop r op yl Nitr ile 5d . After addition of diazoacetonitrile
over a period of 4 h under reflux, 5d was obtained in 67% yield
(0.57 g, white powder) as a 1/1 mixture of diastereomers a and
b. Rf 0.4 (hexane:EtOAc, 8:2). 1H NMR (CDCl3) δ 1.09 (t, J )
7.3 Hz, 3Ha,b), 1.51-2.01 (m, 4Ha,b), 4.72-4.25 (m, 4Ha,b),
7.18-7.30 (m, 4Ha,b). 13C NMR (CDCl3) δ 12.5, 12.8, 15.0, 15.7,
18.0, 20.1, 32.6, 35.7, 71.0, 71.2, 71.4, 95.3, 95.8, 116.5, 118.1,
126.2, 127.1, 127.3, 127.4, 127.6, 127.8, 137.2, 137.3, 137.5.
Syn th esis of Cyclop r op yl Am id es 6a -d . A typical experi-
mental procedure is given for the synthesis of 6a . To a solution
of cyclopropyl nitrile 5a (3.8 g, 18.9 mmol, 1 equiv) in 50 mL of
freshly distilled t-BuOH was added powdered KOH (3.18 g, 3
equiv). The solution was heated to reflux for 4 h, cooled to room
temperature, and diluted with 20 mL of H2O. The precipitate
was collected and washed with hexane to afford cyclopropyl
(14) Loudon, G. M.; Radhakrishna, A. S.; Almond, M. R.; Blodgett,
J . K.; Boutin, R. H. J . Org. Chem. 1984, 49, 4272-4276.
(15) Enantiomeric excess was determined by HPLC using a Chiralcel
OD column.
(16) Houben-Weyl, Methoden der Organishen Chemie, Stickstoff-
Verbindungen I, Band 10/4; Mu¨ller, F., Ed.; G. Thieme Verlag:
Stuttgart, 1968.
(17) Trogen, L. H. Acta Chem. Scand. 1993, 47, 841-842.

308 J . Org. Chem., Vol. 66, No. 1, 2001
Notes
amide 6a in 75% yield (3.10 g, white powder). 1H NMR (DMSO-
d6) δ 1.31 (dd, J ) 5.5 and 9.6 Hz, 1H), 1.56 (dd, J ) 5.5 and 7.1
Hz, 1H), 2.15 (dd, J ) 7.1 and 9.6 Hz, 1H), 4.72-5.04 (m, 4H),
6.96 (brs, 1H), 7.27-7.30 (m, 4H), 7.56 (brs, 1H). 13C NMR
(DMSO-d6) δ 18.2, 29.6, 70.8, 70.9, 95.2, 127.4, 138.8, 168.5.
Cyclop r op yl a m id e 6b (10). Synthesized from the mixture
of diastereomers 5b, 6b was obtained as the single trans
diastereomer (white powder, 0.250 g, 80%). 1H NMR (DMSO-
d6) δ 2.60 (d, J ) 7.3 Hz, 1H), 3.09 (d, J ) 7.3 Hz, 1H), 4.62-
4.95 (m, 4H), 7.10 (brs, 1H), 7.21-7.31 (m, 9H), 7.69 (brs, 1H).
13C NMR (DMSO-d6) δ 34.4, 35.3, 70.5 (2C), 96.5, 126.3, 127.2,
127.3, 127.9, 128.1, 135.3, 138.3, 138.5, 168.0.
Cyclop r op yl Am id e 6c. After 12 h under reflux, the reaction
was quenched with saturated NaCl and extracted four times
with CHCl3 and two times with Et2O. The combined organic
layers were dried over MgSO4 and filtered, and the solvents were
removed under reduced pressure. 6c was obtained, after column
chromatography (CH2Cl2:EtOH, 95:5) over silica, as a white
powder (Rf 0.3, 0.510 g, 70%). 1H NMR (CDCl3) δ 1.33 (s, 3H),
1.40 (s, 3H), 1.76 (s, 1H), 4.28 (d, J ) 14.0 Hz, 1H), 5.00 (s, 2H),
5.04 (d, J ) 14.0 Hz, 1H), 5.60 (brs, 1H), 6.49 (brs, 1H), 7.15-
7.20 (m, 2H), 7.23-7.28 (m, 2H). 13C NMR (CDCl3) δ 15.2, 21.9,
30.4, 38.0, 70.4, 70.7, 97.6, 126.7, 127.2, 127.5, 137.1, 137.8,
171.2.
Cyclop r op yl Am id e 6d . Synthesized from the mixture of
diastereomers 5d . After 3 h under reflux, the reaction was
quenched with saturated NaCl and extracted four times with
CHCl3 and two times with Et2O. The combined organic layers
were dried over MgSO4 and filtered, and the solvents were
removed under reduced pressure. 6d was obtained as the single
trans diastereomer after column chromatography (CH2Cl2:EtOH,
95:5) over silica (white powder, Rf 0.4, 0.350 g, 80%). 1H NMR
(CDCl3) δ 1.06 (t, J ) 7.3 Hz, 3H), 1.51-1.88 (m, 4H), 4.89-
5.05 (m, 4H), 5.61 (brs, 1H), 6.00 (brs, 1H), 7.16-7.26 (m, 4H).
13C NMR (CDCl3) δ 13.3, 20.6, 35.0, 35.4, 71.0, 71.1, 97.6, 127.0,
127.6, 135.2, 137.1, 137.9, 172.2.
Syn th esis of Cyclop r op yl N-Meth yl Ca r ba m a tes 7a -d .
A typical experimental procedure is given for the synthesis of
7a . To a solution of cyclopropyl amide 6a (2 g, 9.1 mmol, 1 equiv)
in 100 mL of anhydrous MeOH was added powdered KOH (1.28
g, 2.5 equiv). The solution was cooled to 0 °C and iodobenzene
diacetate (2.94 g, 1 equiv) was added in one portion. The mixture
was stirred 20 min at 0 °C and 5 h at room temperature. Water
(20 mL) was then added, and the aqueous phase was extracted
three times with CH2Cl2. The combined organic layers were
washed with saturated NaCl, dried over MgSO4, filtered, and
evaporated under reduced pressure. Chromatography over silica
(hexane:EtOAc, 6:4) afforded cyclopropyl N-methyl carbamate
7a in 73% yield (white powder, Rf 0.3, 1.67 g). 1H NMR (CDCl3)
δ 0.99 (m, 1H), 1.47 (m, 1H), 3.14 (m, 1H), 3.67 (s, 3H), 4.89-
5.11 (m, 5H), 7.14-7.25 (m, 4H). 13C NMR (CDCl3) δ 20.9, 34.8,
52.2, 71.0, 71.5, 93.0, 127.4, 127.5, 127.6, 138.2, 138.3, 157.3.
HMRS calcd for C13H14NO4 (M - H)+ 248.0922, found 248.0936.
Cyclop r op yl N-m eth yl ca r ba m a te 7b (11) (white powder,
0.180 g, 86%): Rf 0.5 (hexane:EtOAc, 6:4). 1H NMR (CDCl3) δ
2.42 (d, J ) 5.2 Hz, 1H), 3.49 (brs, 1H), 3.70 (s, 3H), 4.70 (m,
2H), 5.08 (m, 2H), 5.18 (brs, 1H), 7.05 (m, 1H), 7.18-7.31 (m,
8H). 13C NMR (CDCl3) δ 38.3, 40.9, 52.3, 71.2, 71.4, 95.1, 126.4,
127.2, 127.5, 127.6, 127.8, 128.3, 136.8, 137.8, 138.2, 157.1.
HMRS calcd for C19H19NO4 (M)+ 325.1314, found 325.1333.
Cyclop r op yl N-m eth yl ca r ba m a te 7c (white powder, 0.240
g, 87%): Rf 0.5 (hexane:EtOAc, 7:3). 1H NMR (CDCl3) δ 1.13 (s,
3H), 1.31 (s, 3H), 2.71 (d, J ) 4.3 Hz, 1H), 3.69 (s, 3H), 4.84-
5.08 (m, 5H), 7.14-7.24 (m, 4H). 13C NMR (CDCl3) δ 13.8, 19.7,
27.5, 41.4, 52.2, 70.7, 71.0, 95.5, 127.0, 127.3, 127.5, 138.0, 138.4,
157.6. HMRS calcd for C15H20NO4 (M + H)+ 278.1392, found
278.1389.
Cyclop r op yl N-m eth yl ca r ba m a te 7d (white powder, 0.120
1
g, 91%): Rf 0.3 (hexane:EtOAc, 7:3). H NMR (CDCl3) δ 1.08 (t,
J ) 7.3 Hz, 3H), 1.15-1.19 (m, 1H), 1.47-1.64 (m, 2H), 2.70
(brs, 1H), 3.67 (s, 3H), 4.86-5.09 (m, 5H), 7.16-7.26 (m, 4H).
13C NMR (CDCl3) δ 13.3, 19.5, 34.7, 39.3, 52.0, 70.9, 71.1, 95.4,
127.1, 127.3, 127.4, 138.1, 138.4, 157.3. HMRS calcd for C15H19
-
NO4 (M)+ 277.1314, found 277.1358.
Syn th esis of Am in o Acid Der iva tives. A typical experi-
mental procedure is given for the synthesis of 3-[2H]-2-meth-
oxycarbonylamino-propionic acid methyl ester 8a . A 10 mL
flame-dried reaction vessel containing Pd 10 wt % on C (0.053
g, 25 mol %) was air evacuated. A pressure of 0.3 Bar of
deuterium gas was introduced at room temperature, and the
catalyst was vigorously stirred for 30 min. The gas was evacu-
ated and replaced by a fresh aliquot of D2. This operation was
repeated three times. Cyclopropyl N-methyl carbamate 7a (0.05
g, 0.2 mmol, 1 equiv) in 2 mL of anhydrous EtOAc was then
added. The solution was vigorously stirred at room temperature,
under 1 Bar of D2, for 4 h. The catalyst was filtered, and the
solvent was removed under reduced pressure. The crude was
taken in MeOH and treated, at 0 °C, with diazomethane. After
evaporation of the solvent and column chromatography over
silica (hexane:EtOAc, 7:3), â-deuterated alanine derivative 8a
(oil, Rf 0.3, 0.035 g) is obtained in 95% yield and 80% isotopic
purity. 1H NMR (CDCl3) δ 1.38 (t like, J ) 5 Hz, 2H), 3.67 (s,
3H), 3.74 (s, 3H), 4.35 (m, 1H), 5.21 (brs, 1H). 13C NMR (CDCl3)
δ 18.4 (t), 49.5, 52.2, 52.4, 156.2, 173.5. 2H NMR (CHCl3) δ 1.39.
HMRS calcd for C6H10DNO4 (M)+ 162.0750, found 162.0747.
3-[2H]-2-Meth oxycar bon ylam in o-3-ph en ylpr opion ic acid
m eth yl ester 8b (oil, 0.034 g, 93%, 93% i.e.): Rf 0.4 (hexane:
EtOAc, 7:3). 1H NMR (CDCl3) δ 3.09 (brd, 1H), 3.65 (s, 3H), 3.71
(s, 3H), 4.64 (t like, J ) 5.3 Hz, 1H), 5.11 (brd, 1H), 7.11 (m,
2H), 7.23-7.31 (m, 3H). 13C NMR (CDCl3) δ 37.9 (t), 52.3 (2C),
2
54.6, 127.1, 128.6, 129.2, 135.6, 156.2, 172.0. H NMR (CHCl3)
δ 3.09. HMRS calcd for C12H14DNO4 (M)+ 238.1063, found
238.1068.
3-[2H ]-2-Met h oxyca r b on yla m in o-2,2-d im et h ylp r op ion -
ic a cid m eth yl ester 8c was prepared as described for 8a using
80 mol % of Pd/C and with a reaction time of 12 h (oil, 0.019 g,
93%, 71% i.e.): Rf 0.2 (hexane:EtOAc, 8:2). 1H NMR (CDCl3) δ
1.18 (s, 6H), 3.26 (m, 1H), 3.64 (s, 3H), 3.67 (s, 3H), 5.13 (brs,
1H). 13C NMR (CDCl3) δ 22.9, 43.5, 48.4 (t), 52.0, 52.1, 157.3,
177.5. 2H NMR (CHCl3) δ 3.26. HMRS calcd for C8H14DNO4 (M)+
190.1063, found 190.1068.
2-(1-[2H]-1-Meth oxyca r bon yla m in o-m eth yl)bu tyr ic a cid
m eth yl ester 8d was prepared as described for 8c (oil, 0.017 g,
84%, 74% i.e.): Rf 0.2 (hexane:EtOAc, 8:2). 1H NMR (CDCl3) δ
0.92 (t, J ) 7.4 Hz, 3H), 1.52-1.67 (m, 2H), 2.54 (m, 1H), 3.28
(m, 1H), 3.32 (m, residual H), 3.64 (s, 3H), 3.69 (s, 3H), 5.03
(brs, 1H). 13C NMR (CDCl3) δ 11.4, 22.8, 41.3 (t), 46.8, 51.7, 52.1,
157.0, 175.3. 2H NMR (CHCl3) δ 2.53, 3.35. HMRS calcd for
C8H14DNO4 (M)+ 190.1063, found 190.1087.
Ack n ow led gm en t. Dr. J . Albert Ferreira is grate-
fully acknowledged for reviewing this manuscript.
Su p p or tin g In for m a tion Ava ila ble: Reproductions of 1H
and 13C NMR spectra of key intermediates 7a -d and of labeled
amino acid derivatives 8a -d . This material is available free
of charge via the Internet at http://pubs.acs.org.
J O001126H