Synthesis of anisolylated aspartyl and glutamyl tripeptides

Article abstract of DOI:10.1021/jo951754c

A process has been developed for transforming the β-carboxyl of aspartate and the γ-carboxyl of glutamate into anisolyl ketones. These ketones are occasional byproducts in peptide synthesis, resulting from deprotection or resin-removal processes in the presence of anisole as a scavenger. The ketone amino acids have been incorporated in a tripeptide by coupling with CBMIT. During peptide bond formation the keto group of the glutamyl residue required protection, which was provided as the ethylene dithioketal.

Full text of DOI:10.1021/jo951754c

J . Org. Chem. 1996, 61, 715-721
715
Syn th esis of An isolyla ted Asp a r tyl a n d Glu ta m yl Tr ip ep tid es
Fabienne Berre´e, Kieyoung Chang, Agust´ın Cobas, and Henry Rapoport*
Department of Chemistry, University of California, Berkeley, California 94720
Received September 26, 1995X
A process has been developed for transforming the â-carboxyl of aspartate and the γ-carboxyl of
glutamate into anisolyl ketones. These ketones are occasional byproducts in peptide synthesis,
resulting from deprotection or resin-removal processes in the presence of anisole as a scavenger.
The ketone amino acids have been incorporated in a tripeptide by coupling with CBMIT. During
peptide bond formation the keto group of the glutamyl residue required protection, which was
provided as the ethylene dithioketal.
In tr od u ction
which is quite efficient and may have broad generality.
The differentially protected aspartate 2 (Scheme 1),
readily prepared from aspartic acid,5 was converted to
the corresponding aryl ketone via the isoxazolidide 3.6
Trial experiments showed the anisolyllithium to be far
superior to the Grignard reagent.
The potential importance of artifacts produced during
peptide synthesis as a result of deprotection and resin-
removal protocols has been dramatically demonstrated
in a recent example involving anti-inflammatory unde-
capeptides.1 In that case, a byproduct formed by acyla-
tion of the anisole scavenger by the γ-glutamyl carboxyl
led to a component more biologically active than the
parent peptide.
The structure of this component with enhanced potency
was established by comparison of NMR spectra with
those of authentic samples of 2-amino-5-(methoxyphe-
nyl)-5-oxopentanoates (γ-anisolylated glutamates, An-
Glu2 ). This comparison also established that the anisoly-
lated component was approximately 94% para and 6%
ortho isomer.
To pursue these findings further, we have developed
methods for synthesizing tripeptides containing either
ortho or para 2-amino-4-(methoxyphenyl)-4-oxobutanoates
(â-anisolylated aspartates, AnAsp) or AnGlu residues.
Our examples have central AnAsp or AnGlu residues
flanked by isoleucine at the carboxy terminus and me-
thionine at the amino terminus. They were chosen for
subsequent elaboration into anti-inflammatory peptides3
and to provide a modest degree of generality for the
synthesis of such ketone-containing peptides.
With o-anisolyllithium, prepared from o-bromoanisole,
the reaction was straightforward. The case of the para
isomer, however, was more complex. The complication
arose from ortho metalation of p-bromoanisole by the
initially formed p-anisolyllithium when the reaction was
carried out in ether or pentane. Thus the solution
contained two aryllithium reagents: p-anisolyllithium
and (5-bromo-2-methoxyphenyl)lithium. The major prod-
uct, p-anisolyllithium, then could be purified by precipi-
tation with hexane and re-solution for ketone formation.7
These side products were minimized when halogen-
metal exchange was performed in THF. For both isomers
of ketones 4 the yields were good: 73% para, 76% ortho.
In preparation for peptide formation, both tert-butyl
groups were removed and the amino reprotected as the
N-BOC acid 5.
P r ep a r a tion of An isolyla ted Asp a r tyl Tr ip ep -
tid es. The preparation of the tripeptides Met-AnAsp-
Ile is shown in Scheme 2. Coupling proceeded from the
amino terminus using the carbonylbis(3-methylimidazo-
lium triflate) (CBMIT) reagent.8 For coupling to Ile-
OCH3, the yields of dipeptides 6 were 72% and 80% for
the ortho and para isomers, respectively, and 86% (ortho)
and 92% (para) in the coupling of Met to 6 to form
tripeptides 8.
Peptide formation was uneventful, and no changes in
the normal procedures were required to accommodate the
keto function. For flexibility in continuing peptide
synthesis, the tripeptide was made available as the
N-BOC carboxylic acid 9 and the amine hydrochloride
methyl ester 10.
P r ep a r a t ion a n d P r ot ect ion of γ-An isolyla t ed
Glu ta m a te. Both the ortho and para isomers of the
γ-anisolylated glutamates 11 were prepared in good yield
(65%) from the γ-carboxylic acid following the sequence
described for the aspartate analogue.1
Resu lts a n d Discu ssion
P r ep a r a tion of â-An isolyla ted Asp a r ta tes. There
has been a recent flurry of interest in the synthesis of
oxo-R-amino acids.4 We now present another method
X Abstract published in Advance ACS Abstracts, J anuary 15, 1996.
(1) Thomas, H. A.; Ling, N; Wei, E. T.; Berre´e, F.; Cobas, A.;
Rapoport, H. J . Pharmacol. Expt. Ther. 1993, 267, 1321. Other
examples of anisolyl ketone formation are cited in this reference.
(2) The prefix An will be used to designate the anisolyl ketone
formed from anisole and the γ-carboxyl of glutamic acid and the
â-carboxyl of aspartic acid, thus AnGlu and AnAsp. A superscript will
be used to designate ortho or para regiochemistry, e.g., AnpAsp, Ano-
Glu.
(3) Work in progress by H. A. Thomas and E. T. Wei. Direct
synthesis of pure para and ortho isomers of the anisolylated derivatives
may provide information on the relative contribution of these two
isomers to activity.
(4) Some selected references: (a) Ibrahim, H. H.; Lubell, W. D. J .
Org. Chem. 1993, 58, 6438. (b) Ko, K.-Y.; Lee, K.-I.; Kim, W.-J .
Tetrahedron Lett. 1992, 33, 6651. (c) Ho, T. L.; Gopalan, B.; Nestor, J .
J ., J r. J . Org. Chem. 1986, 51, 2405. (d) Ezquerra, J .; de Mendoza, J .;
Pedregal, C.; Ramirez, C. Tetrahedron Lett. 1992, 33, 5589. (e) J ackson,
R. F. W.; Wishart, N.; Wood, A.; J ames, K.; Wythes, M. J . J . Org. Chem.
1992, 57, 3397. (f) Burger, K.; Rudolph, M.; Neuhauser, H. Liebigs Ann.
Chem. 1991, 1365. (g) Baldwin, J . E.; Adlington, R. M.; Godfrey, C. R.
A.; Gollins, D. W.; Smith, M. L.; Russel, A. T. Synlett 1993, 51.
(5) Bergmeier, S. C.; Coba´s, A.; Rapoport, H. J . Org. Chem. 1993,
58, 2369.
(6) Cupps, T. L.; Boutin, R. H.; Rapoport, H. J . Org. Chem. 1985,
50, 3972.
(7) (a) Fraenkel, G.; Dayagi, S.; Kobayashi, S. J . Phys. Chem. 1968,
72, 953. (b) Glaze, W. H.; Ranade, A. C. J . Org. Chem. 1971, 36, 3331.
(c) Gilman, H.; Langham, W.; J acoby, A. L. J . Am. Chem. Soc. 1939,
61, 106. (d) Gilman, H.; J acoby, A. L. J . Org. Chem. 1938, 3, 108.
(8) Saha, A. K.; Schultz, P.; Rapoport, H. J . Am. Chem. Soc. 1989,
111, 4859.
0022-3263/96/1961-0715$12.00/0 © 1996 American Chemical Society

716 J . Org. Chem., Vol. 61, No. 2, 1996
Sch em e 1. An isolyla ted Asp a r ta te
Berre´e et al.
Clean N-BOC or tert-butyl ester cleavage,10 leaving the
ketal intact, could not be achieved. Any acid treatment
sufficient to remove the N-BOC immediately led to in situ
formation of pyrroline 17.
Sch em e 2. P r ep a r a tion of An isolyla ted Asp a r tyl
Tr ip ep tid es
An obvious solution was to protect the ketone as the
much more acid stable dithioketal, provided that compat-
ible conditions could be found for subsequent regenera-
tion of the ketone. Dithioketal was readily formed by
exchange with 1,2-ethanedithiol, catalyzed by BF3‚Et2O.
Thus the thioketal was available as the N-BOC derivative
13 or the NH2 compound 14.10b For application in peptide
synthesis, both the N-BOC and tert-butyl ester were acid-
cleaved, giving 15 from which the N-BOC acid 16 was
prepared.
To develop conditions for cleavage of the dithioketal,
applicable after incorporation into our tripeptide, we used
13 as the substrate. When applied to 13, a series of
recently reported promising methods all failed: photo-
chemical,11 reflux in DMSO,12 exchange catalyzed by
TMSOTf,13 1-fluoro-2,4,6-trimethylpyridinium triflate.14
From all reactions, 13 was recovered in high yield
unchanged. A method that was quite effective was
AgNO2/I2,15 but this reagent cannot be used in the
presence of methionine residues, which are oxidized to
sulfoxides.
A variation16 on an older method was finally found to
satisfy all the requirements. Thus treatment of 13 at
room temperature with Hg(ClO4)2/CHCl3/CH3OH/H2O
gave an almost quantitative yield of 11. Furthermore,
methionine and its N-BOC tert-butyl ester were recovered
unchanged from a similar treatment.
P r ep a r a tion of An isolyla ted Glu ta m yl Tr ip ep -
tid es. With the ethylene dithioketal N-BOC anisolylated
glutamic acids 16 at hand, we proceeded to prepare the
target tripeptide as shown in Scheme 4. Coupling with
A complication in the glutamate series, however,
immediately appeared because of the juxtaposition of the
ketone and amine, resulting in intramolecular pyrroline
formation. Protection of the keto group was required,
and various possibilities were considered under the
constraints of subsequent utilization in peptide forma-
tion. Alcohol formation would adequately avoid pyrroline
production but was not pursued because of diastereomers
and the necessity to protect and reoxidize, which would
be incompatible with many amino acid residues in a
peptide.
The protecting regimen of choice appeared to be ketal
protection, which is presented in Scheme 3. Normal,
acid-catalyzed dimethyl or ethylene ketal formation was
poor, but 2-methoxy-1,3-dioxolane with catalytic triflic
acid9 gave 75-79% yields of the ethylene ketals 12.
Problems then arose in utilizing 12 in peptide synthesize.
(10) (a) Kaiser, Sr., E.; Picart, F.; Kubiak, T.; Tam, J . P.; Merrifield,
R. B. J . Org. Chem. 1993, 58, 5167. (b) Gibson, F. S.; Bergmeier, S. C.
J . Org. Chem. 1994, 59, 3216.
(11) Epling, G. A.; Wang, Q. Tetrahedron Lett. 1992, 33, 5909;
Synlett 1992, 335.
(12) Rao, C. S.; Chandrasekharam, M.; Ila, H.; J unjappa, H.
Tetrahedron Lett. 1992, 33, 8163.
(13) Ravindranathan, T.; Chavan, S. P.; Tejwani, R. B.; Varghese,
J ., P. J . Chem. Soc., Chem. Commun. 1991, 1750.
(14) Kiselyov, A. S.; Strekowski, L. Tetrahedron 1993, 49, 2151.
(15) Nishide, K.; Yokota, K.; Nakamura, D.; Sumiya, T.; Node, M.;
Ueda, M.; Fuji, K. Tetrahedron Lett. 1993, 34, 3425.
(16) Aoyagi, S.; Wang, T.-C.; Kibayashi, C. J . Am. Chem. Soc. 1993,
115, 11393.
(9) J ohnson, S. J .; Kesten, S. R.; Wise, L. D. J . Org. Chem. 1992,
57, 4746.

Synthesis of Anisolylated Aspartyl and Glutamyl Tripeptides
J . Org. Chem., Vol. 61, No. 2, 1996 717
Sch em e 3. Keta ls of An isolyla ted Glu ta m a te
sodium-benzophenone; pentane was distilled from lithium
aluminum hydride; nitromethane, DMF, N-methylmorpholine,
and triethylamine were distilled from calcium hydride and
stored over 4A molecular sieves; and methanol was distilled
from Mg. Final solutions before rotary evaporation were dried
over Na2SO4. The isoleucine methyl ester was freed im-
mediately before use from its hydrochloride.17
Sch em e 4. P r ep a r a tion of An isolyla ted Glu ta m yl
Tr ip ep tid es
r-ter t-Bu tyl N-(ter t-Bu toxycar bon yl)-L-aspar tate â-Isox-
a zolid id e (3). N-Methylmorpholine (4.0 mL, 36.2 mmol) was
added to a solution of R-tert-butyl N-(tert-butoxycarbonyl)-L-
aspartate (2, 10.5 g, 36.1 mmol)4 in THF (200 mL) at -20 °C,
and after 1 min isobutyl chloroformate (4.7 mL, 36.2 mmol)
was added. The mixture was stirred for 5 min and then a
suspension of isoxazolidine hydrochoride (4.36 g, 39.4 mmol)
and triethylamine (5.5 mL, 39.8 mmol) in DMF (100 mL) was
added. The reaction mixture was stirred for 15 min at -15
°C and 2.5 h at rt and then was partitioned between ethyl
acetate (400 mL) and 1 M H3PO4 (300 mL). The aqueous layer
was extrated with ethyl acetate (200 mL), and the combined
organic layer was washed with saturated NaHCO3 (2 × 300
mL), dried, and evaporated to give an oil which was chromato-
graphed (ethyl acetate/hexane 1/1) to give 3 (11.8 g, 95%) as
an oil: 1H NMR δ 5.61 (d, J ) 8.7, 1H), 4.42 (m, 1H), 3.94 (t,
J ) 6.8, 2H), 3.66 (t, J ) 6.5, 2H), 3.08 (dd, J ) 4.2, 6.9, 1H),
2.83 (dd, J ) 4.2, 6.9, 1H), 2.29 (m, 2H), 1.43 (s, 9H), 1.41 (s,
9H); 13C NMR δ 170.4, 170.1, 155.5, 81.6, 79.3, 69.1, 50.2, 42.9,
35.0, 28.2, 27.7, 27.3; [R]20 +15.7° (c 1, CHCl3). Anal. Calcd
D
for C16H28N2O6: C, 55.8; H, 8.2; N, 8.1. Found: C, 55.4; H,
7.9; N, 8.0.
P r ep a r a tion of p-An isolyllith iu m . n-Butyllithium (31.9
mL, 2.35 M in hexane, 75 mmol) was added dropwise over a
period of 40 min to a solution of p-bromoanisole (9.5 mL, 75
mmol) in THF (60 mL) at -78 °C. The reaction mixture was
stirred for 15 min at -78 °C, and then stirring was continued
as pentane (250 mL) was added dropwise. The precipitate was
allowed to settle, and the solvent was cannulated off. Pentane
(150 mL) was again added dropwise and then cannulated off
as a wash. After being washed one more time with pentane,
the precipitate was allowed to reach rt, ether (90 mL) was
added, and the resulting solution was found to be 0.54 M by
titration with diphenylacetic acid. The yield of p-anisolyl-
lithium was about 70%. An aliquot of this solution was
quenched with H2O, extracted with ether, dried, and evapo-
rated to give anisole, containing <2% (limit of detection) of
isoleucine methyl ester mediated by CBMIT gave the
peptides 18. Following removal of the BOC group from
18, the amine 19 formed was coupled with N-BOC
methionine resulting in ethylene dithioketal tripeptides
20. In all the couplings the yields were about 70%.
Dethioketalization then was readily effected in 85-
88% yield using the Hg(ClO4)2 reagent. For possible use
in extended peptide synthesis, the keto tripeptide N-BOC
methyl ester 21 also was converted to the carboxylic acid
22.
The protocols thus developed should be applicable to
a wide variety of keto peptides.
1
4-bromoanisole as determined by H NMR (doping assay).
ter t-Bu tyl (S)-2-((ter t-Bu toxycar bon yl)am in o)-4-(4-m eth -
oxyp h en yl)-4-oxobu ta n oa te (4p). To a solution of the
isoxazolidide 3 (6.16 g, 17.9 mmol) in ether (100 mL) at -20
°C was added dropwise a solution of p-anisolyllithium in ether
(75 mL, 0.54 M, 40.5 mmol, 225 mol %) over a period of 20
min, and the reaction mixture was stirred for 45 min. After
the addition of NaH2PO4 (1 M, 100 mL) and vigorous stirring
for 2 min, the mixture was extracted with EtOAc (2 × 100
Exp er im en ta l Section
Gen er a l. NMR spectra were obtained in CDCl3 unless
otherwise noted and are referenced to internal tetramethyl-
silane; coupling constants are reported in hertz. Chromatog-
raphy was carried out using silica gel 230-400 mesh. TLC
analysis were performed on aluminum-backed silica gel F250
0.2 mm plates. All reactions were conducted under a nitrogen
or argon atmosphere. THF and ether were distilled from
,
(17) Toniolo, C. Biopolymers 1971, 10, 1707.

718 J . Org. Chem., Vol. 61, No. 2, 1996
Berre´e et al.
mL), dried, evaporated, and chromatograped (hexane/EtOAc,
(3 mL) was added, and the mixture was stirred for 1 min and
partitioned between saturated NaHCO3 (30 mL) and ethyl
acetate (30 mL). The aqueous layer was extracted with ethyl
acetate (30 mL), the combined organic layers were dried and
evaporated, and the residue was chromatographed (EtOAc/
Hexane, 1/1) to give 1.37 g (80%) of dipeptide 6p as an oil,
which was crystallized from CHCl3/hexane: mp 114-117 °C;
1H NMR δ 7.93 (d, J ) 8.9, 2H), 7.19 (br d, J ) 8.2, 1H), 6.93
(d, J ) 8.9, 2H), 5.89-5.86 (m, 1H), 4.71 (m, 1H), 4.52 (dd, J
) 8.7, 4.9, 1H), 3.88 (s, 3H), 3.68 (s, 3H), 3.25 (dd, J ) 17.9,
6.4, 1H), 1.95-1.89 (m, 1H), 1.46 (s, 9H), 1.46-1.40 (m, 1H),
1.25-1.19 (m, 1H), 0.94-0.90 (m, 6H); 13C NMR δ 197.5, 171.8,
171.0, 163.8, 155.5, 130.5, 129.3, 113.7, 80.3, 56.7, 55.5, 52.0,
50.5, 39.9, 37.7, 28.3, 25.0, 15.5, 12.0; [R]25D +80.9° (c 1, CHCl3).
Anal. Calcd for C23H34N2O7: C, 61.3; H, 7.6; N, 6.2. Found:
C, 61.4; H, 7.7; N, 6.2.
4/1), to give 4p (4.92 g, 73%) as an oil which solidified by
1
standing: mp 92 °C; H NMR δ 7.91 (m, 2H), 6.92 (m, 2H),
5.59 (d, J ) 8.4, 1H), 4.52 (m, 1H), 3.85 (s, 3H), 3.61 (dd, J )
4.25, 17.6, 1H), 3.37 (dd, J ) 4.2, 17.6, 1H), 1.42 (s, 9H), 1.41
(s, 9H); 13C NMR δ 196.3, 170.5, 163.8, 155.7, 130.4, 129.5,
113.8, 81.9, 79.6, 55.5, 50.4, 40.6, 28.3, 27.8; [R]20 +24.3° (c
D
1.5, CHCl3). Anal. Calcd for C20H29NO6: C, 63.3; H, 7.7; N,
3.7. Found: C, 62.9; H, 7.6; N, 4.0.
ter t-Bu tyl (S)-2-((ter t-bu toxycar bon yl)am in o)-4-(2-m eth -
oxyp h en yl)-4-oxobu ta n oa te (4o) was prepared as described
for the corresponding para isomer, using o-anisolyllithium.7b
From 12g of 3, after chromatography (hexane/EtOAc, 4/1), was
isolated 10.0 g, 76% yield, of 4o as an oil: 1H NMR δ 7.77 (d,
J ) 7.7, 1H), 7.48 (m, 1H), 6.99 (m, 2H), 5.57 (d, J ) 8.6, 1H),
4.50 (m, 1H), 3.92 (s, 3H), 3.67 (dd, J ) 4.5, 18.5, 1H), 3.47
(dd, J ) 3.9, 18.5, 1H), 1.44 (s, 9H), 1.43 (s, 9H); 13C NMR δ
199.0, 170.8, 159.1, 155.7, 134.2, 130.5, 126.7, 120.6, 111.5,
81.6, 79.4, 55.5, 50.5, 46.5, 28.3, 27.9; [R]20D +25.5° (c 1, CHCl3).
Anal. Calcd for C20H29NO6: C, 63.3; H, 7.7; N, 3.7. Found:
C, 63.1; H, 7.8; N, 3.7.
(S)-2-((ter t-Bu toxyca r bon yl)a m in o)-4-(4-m eth oxyp h e-
n yl)-4-oxobu ta n oic Acid (BOC-An pAsp , 5p). A solution of
ketone 4p (4.92 g, 13.0 mmol) in TFA (100 mL) was stirred
for 2.5 h. The solvent was evaporated at rt, methanol (2 ×
150 mL) was added and evaporated twice, and then ether (100
mL) was added and evaporated to give the intermediate (S)-
2-a m in o-4-(4-m et h oxyp h en yl)-4-oxob u t a n oic a cid t r i-
flu or oa ceta te as a yellow solid: 1H NMR δ (CD3OD) δ 8.02
(m, 2H), 7.04 (m, 2H), 4.40 (t, J ) 5.3, 1H), 3.88 (s, 3H), 3.70
(d, J ) 5.3, 2H); 13C NMR (CD3OD) δ 196.3, 171.6, 165.8, 131.7,
129.6, 115.0, 56.1, 50.1, 38.9.
This salt was dissolved in THF/H2O (1/1, 250 mL), and
BOC2O (5.66 g, 25.9 mmol) was added followed by triethy-
lamine (5.42 mL, 38.91 mmol). The reaction was stirred for 2
h at rt and then was partitioned between H2O (150 mL) and
ethyl acetate (150 mL). The aqueous layer was acidified with
1 M H3PO4 to pH 2 and extracted with ethyl acetate (2 ×
100mL). The residue left after drying and evaporating the
ethyl acetate was chromatograped (hexane/ethyl acetate/acetic
acid, 20/79/1) to give an oil. Removal of the remaining HOAc
by azeotropic distillation with benzene gave a foam which was
triturated with hexane to give 3.36 g (80%) of 5p as a white
solid: mp 114-117 °C; 1H NMR δ 7.91 (m, 2H), 6.92 (m, 2H),
5,67 (d, J ) 8.4, 1H), 4.70 (m, 1H), 3.85 (s, 3H), 3.71 (dd, J )
4.4, 18.0, 1H), 3.45 (dd, J ) 4.4, 18.0, 1H), 1.41 (s, 9H); 13C
NMR δ 197.5, 175.8, 164.1, 155.7, 130.6, 129.1, 113.9, 80.2,
55.5, 49.5, 40.5, 28.28; [R]20D +83.3° (c 1, CHCl3). Anal. Calcd
for C16H21NO6: C, 59.4; H, 6.5; N, 4.3. Found: C, 59.1; H,
6.5; N, 4.3.
(S)-2-((ter t-Bu toxca r bon yl)a m in o)-4-(2-(m eth oxyp h e-
n yl)-4-oxobu ta n oic a cid (BOC-An oAsp (5o) was prepared
as described for the para isomer. The intermediate (S)-2-
a m in o-4-(2-m eth oxyp h en yl)-4-oxobu ta n oic a cid tr iflu o-
r oa ceta te displayed the following spectroscopic data: 1H NMR
(CD3OD) δ 7.81 (m, 1H), 7.54 (m, 1H), 7.09 (d, J ) 8.4, 1H),
6.99 (m, 1H), 4.39 (t, J ) 5.1, 1H), 3.91 (s, 3H), 3.75 (d, J )
5.1, 2H); 13C NMR (CD3OD) δ 198.2, 171.5, 161.2, 136.5, 131.6,
126.5, 121.7, 113,3, 56.2, 50.2, 44.7.
BOC-An oAsp -Ile-OCH3 (6o) was prepared as described for
the para isomer. From 3.00 g (9.3 mmol) of 5o was obtained
3.00 g (72%) of 6o as an oil: 1H NMR δ 7.80-7.77 (m, 1H),
7.51-7.45 (m, 1H), 7.16-7.13 (m, 1H), 7.02-6.94 (m, 2H),
5.80-5.78 (m, 1H), 4.68-4.64 (m, 1H), 4.53 (dd, J ) 8.7, 4.9,
1H), 3.90 (s, 3H), 3.77-3.70 (m, 1H), 3.67 (s, 3H), 3.37 (dd, J
) 18.7, 6.3, 1H), 1.50-1.39 (m, 1H), 1.46 (s, 9H), 1.28-1.20
(m, 1H), 0.95-0.87 (m, 6H); 13C NMR δ 200.2, 171.9, 171.2,
159.1, 155.5, 134.4, 130.6, 126.7, 120.6, 111.5, 80.1, 56.7, 55.5,
52.0, 50.8, 45.8, 37.7, 28.3, 24.9, 15.5, 11.6; [R]25
+75.5° (c 1,
D
CHCl3). Anal. Calcd for C23H34N2O7: C, 61.3; H, 7.6; N, 6.2.
Found: C, 61.0; H, 7.6; N, 6.1.
HCl‚An pAsp -Ile-OCH3 (7p). Acetyl chloride (3.2 mL, 45
mmol) was added dropwise to a solution of methanol (1.8 mL,
45 mmol) in ethyl acetate (10 mL) at 0 °C, and the solution
was stirred for 15 min at 0 °C and 1 h at rt. This solution
was added dropwise to a solution of BOC-AnpAsp-Ile-OCH3
(6p, 1.01 g, 2.24 mmol) in ethyl acetate (10 mL) at rt, and the
reaction mixture was stirred for 2 h and then evaporated at
rt. The residue was dissolved in a small amount of methanol,
and ether was added to afford 800 mg (92%) of 7p as a white
solid: mp 155-157 °C; 1H NMR (CD3OD) δ 8.04-8.01 (m, 2H),
7.05 (dd, J ) 7.1, 1.8, 2H), 4.47 (m, 2H), 3.89 (s, 3H), 3.74 (m,
1H), 3.70 (s, 3H), 3.69-3.52 (m, 1H), 1.93 (m, 1H), 1.47 (m,
1H), 1.26 (m, 1H), 0.95 (m, 6H); 13C NMR (CD3OD) δ 195.8,
173.2, 170.3, 116.0, 131.7, 129.8, 115.1, 58.6, 56.2, 52.6, 50.3,
40.4, 38.2, 26.3, 16.1, 11.9; [R]25 -11.2° (c 1, MeOH). Anal.
D
Calcd for C18H27N2O5Cl: C, 55.9; H, 7.0; N, 7.2. Found: C,
56.1; H, 7.2; N, 7.2.
HCl‚An oAsp -Ile-OCH3(7o) was prepared as described for
the para isomer. From 1.81 g, 4.02 mmol of 6o was obtained
1.33 g (86%) of 7o: mp 180-182 °C; 1H NMR (CD3OD) δ 7.89
(dd, J ) 7.8, 1.8, 1H), 7.64-7.58 (m, 1H), 7.19 (d, J ) 8.3,
1H), 7.09-7.03 (m, 1H), 4.47 (m, 2H), 3.99 (s, 3H), 3.83 (dd, J
) 19.5, 3.2, 1H), 3.71 (s, 3H), 3.54 (dd, J ) 19.5, 9.6, 1H), 1.93
(m, 1H), 1.44 (m, 1H), 1.27 (m, 1H), 0.95 (m, 6H);
13C NMR
(CD3OD) δ 198.6, 173.7, 171.2, 161.9, 137.2, 132.3, 127.3, 122.5,
114.1, 59.2, 57.0, 53.3, 51.2, 47.1, 38.8, 27.0, 16.8, 12.6; [R]25
D
+16.9° (c 1, MeOH). Anal. Calcd for C18H27N2O5Cl: C, 55.9;
H, 7.0; N, 7.2. Found: C, 55.5; H, 7.0; N, 6.8.
BOC-Met-An pAsp -Ile-OCH3 (8p). Methyl triflate (0.95
mL, 8.37 mmol) was added dropwise (1 min) to a solution of
CDI (0.68 g, 4.19 mmol) in nitromethane (10 mL) at 0 °C. The
solution was stirred for 5 min, and a solution of BOC-Met (99
mg, 3.96 mmol) and N-methylimidazole (33 µL, 0.41 mmol) in
THF/MeNO2 (10 mL, 1/1) was added (via cannula, 3 min). The
mixture was stirred for 8 min, and a solution HCl‚AnpAsp-
Ile-OCH3 (7p, 800 mg, 2.06 mmol) and N-methylmorpholine
(0.92 mL, 8.36 mmol) in THF/DMF (1/1, 5 mL) was added. The
reaction mixture was stirred for 1.5 h at rt, H2O (3 mL) was
added, and the mixture was stirred for 2 min and then was
partitioned between saturated NaHCO3 (50 mL) and ethyl
acetate (50 mL). The aqueous layer was extracted with ethyl
acetate (50 mL), and the combined organic layer was dried
and evaporated. The residue was chromatographed (EtOAc/
hexane, 3/2) to give 1.17 g (98%) of tripeptide 8p: mp (CH2-
Cl2/hexane) 109-114 °C; 1H NMR δ 7.92 (d, J ) 8.8, 2H), 7.49
(br d, J ) 7.2, 1H), 7.27 (br d, J ) 8.0, 1H), 6.92 (d, J ) 8.8,
2H), 5.27-5.24 (m, 1H), 5.02-5.01 (m, 1H), 4.48 (dd, J ) 8.4,
4.8, 1H), 4.30-4.28 (m, 1H), 3.87 (s, 3H), 3.77-3.71 (m, 1H),
The N-BOC amino acid 5o was isolated in 92% yield: mp
1
113-117 °C; H NMR δ 7.82 (d, J ) 7.7, 1H), 7.49 (m, 1H),
6.97 (m, 2H), 5.61 (m, 1H), 4.66 (m, 1H), 3.92 (s, 3H), 3.72-
3.49 (m, 2H), 1.42 (s, 9H); 13C NMR δ 198.8, 176.8, 159.5, 155.7,
134.7, 130.9, 126.1, 120.7, 111.7, 80.0, 55.5, 49.8, 46.3, 28.3;
[R]20D +59.7° (c 1, CHCl3). Anal. Calcd for C16H21NO6: C, 59.4;
H, 6.5; N, 4.3. Found: C, 59.1; H, 6.5; N, 4.3.
BOC-An pAsp -Ile-OCH3 (6p). Methyl triflate (0.87 mL,
7.65 mmol) was added dropwise (1 min) to a solution of CDI
(0.62 g, 3.82 mmol) in nitromethane (17 mL) at 0 °C. The
solution was stirred for 5 min, and a solution of BOC-AnpAsp
(5p 1.23 g, 3.82 mmol) and N-methylimidazole (30.5 µL, 0.38
mmol) in THF/MeNO2 (12 mL, 1:1) was added (via cannula, 3
min). The mixture was stirred for 5 min, and a solution of
isoleucine methyl ester (1.28 g, 8.8 mmol) and N-methylmor-
pholine (0.84 mL, 7.64 mmol) in THF (4 mL) was added (via
cannula). The reaction mixture was stirred for 2 h at rt, H2O

Synthesis of Anisolylated Aspartyl and Glutamyl Tripeptides
J . Org. Chem., Vol. 61, No. 2, 1996 719
3.71 (s, 3H), 3.22 (dd, J ) 17.9, 7.1, 1H), 2.58 (t, J ) 7.2, 2H),
2.15-1.90 (m, 3H), 2.11 (s, 3H), 1.43-1.22 (m, 2H), 1.43 (s,
9H), 0.93-0.88 (m, 6H); 13C NMR δ 197.3, 171.6, 171.3, 170.4,
163.9, 155.4, 130.5, 129.1, 113.7, 80.2, 56.9, 55.5, 53.7, 52.0,
1H), 3.98-3.94 (m, 1H), 3.96 (s, 3H), 3.69 (s, 3H), 3.57-3.50
(m, 2H), 2.60 (t, J ) 7.8 Hz, 2H), 2.17-2.09 (m, 1H), 2.11 (s,
3H), 1.92-1.85 (m, 1H), 1.51-1.44 (m, 1H), 1.27-1.20 (m, 1H),
0.94-0.89 (m, 6H); 13C NMR (CD3OD) δ 199.0, 173.4, 173.3,
169.6, 160.8, 135.8, 131.4, 127.8, 121.6, 113.3, 58.4, 56.2, 53.5,
49.1, 39.9, 37.3, 31.5, 30.2, 28.2, 25.0, 15.5, 15.3, 11.6; [R]25
D
+59.1° (c 1, CHCl3). Anal. Calcd for C28H43N3O8S: C, 57.8;
H, 7.5; N, 7.2. Found: C, 57.5; H, 7.5; N, 7.4.
52.5, 51.0, 46.5, 38.4, 32.3, 29.6, 26.3, 16.0, 15.1, 11.8; [R]25
D
+13.2° (c 1, CH3OH). Anal. Calcd for C23H36N3O6SCl: C, 53.3;
H, 7.0; N, 8.1. Found: C, 52.9; H, 7.1; N, 7.8.
BOC-Met-An oAsp -Ile-OCH3 (8o) was prepared as de-
scribed for the para isomer. From 800 mg of 7o was obtained
970 mg (81%) of tripeptide 8o: mp (CH2Cl2/hexane) 90-95 °C;
1H NMR δ 7.77 (dd, J ) 7.8, 1.6, 1H), 7.48-7.42 (m, 1H), 7.34-
7.31 (m, 1H) 7.24-7.15 (m, 1H), 6.99-6.91 (m, 2H), 5.20-5.18
(m, 1H), 4.98-4.94 (m, 1H), 4.46 (dd, J ) 8.4, 4.9, 1H), 4.26
(m, 1H), 3.87 (s, 3H), 3.68 (dd, J ) 18.9, 3.4, 1H), 3.61 (s, 3H),
3.33 (dd, J ) 18.7, 7.1, 1H), 2.54 (t, J ) 7.2, 2H), 2.11-2.05
(m, 1H), 2.07 (s, 3H), 1.94-1.86 (m, 2H), 1.44-1.18 (m, 2H),
1.40 (s, 9H), 0.91-0.86 (m, 6H); 13C NMR δ 199.9, 171.6, 171.2,
170.6, 159.2, 155.4, 134.5, 130.7, 126.5, 120.6, 111.5, 80.2, 56.9,
55.5, 53.7, 51.9, 49.3, 45.9, 37.4, 31.7, 30.1, 28.2, 25.0, 15.5,
ter t-Bu tyl (S)-2-((ter t-Bu toxyca r bon yl)a m in o)-5-[2,2-
(1,3-d ioxola n yl)]-5-(4-m eth oxyp h en yl)p en ta n oa te (12p).
Triflic acid (5 µL, 0.06 mmol) was slowly added at 0 °C to a
solution of ketone 11p (0.45 g, 1.14 mmol) and 2-methoxy-1,3-
dioxolane (0.24 g, 2.35 mmol) in CH2Cl2 (1 mL). The mixture
was stirred at rt for 1 h, Et2O was added, and the organic layer
was washed with saturated NaHCO3 (1×) and H2O (2×), dried,
filtered, and evaporated. The residue was purified by chro-
matography (EtOAc/hexanes, 4/1) to give 0.39 g (79%) of 12p
1
as a white solid: mp 106-107 °C; H NMR δ 1.42 (s, 18H),
1.66-1.94 (m, 2H), 1.86 (m, 2H), 3.76 (s, 2H), 3.80 (s, 3H), 3.98
(s, 2H), 4.14 (1H), 5.01 (1H), 6.85 (d, J ) 7.5, 2H), 7.33 (d, J )
7.5, 2H); 13C NMR δ 26.8, 27.9, 28.3, 36.0, 53.2, 55.2, 64.4,
64.5, 79.4, 81.5, 109.8, 113.4, 126.8, 134.4, 155.3, 159.3, 171.8;
[R]22D -8.9° (c 1, EtOH). Anal. Calcd for C23H35NO7: C, 63.1;
H, 8.1; N, 3.2. Found: C, 62.8; H, 8.1; N, 3.6.
15.3, 11.6; [R]25 +54.0° (c 1, CHCl3). Anal. Calcd for
D
C28H43N3O8S: C, 57.8; H, 7.5; N, 7.2. Found: C, 58.0; H, 7.6;
N, 7.0.
BOC-Met-An pAsp -Ile-OH (9p). To a solution of BOC-Met-
AnpAsp-Ile-OCH3 (8p, 620 mg, 1.07 mmol) in dioxane (8mL)
at rt was added a solution of lithium hydroxide monohydrate
(720 mg, 17 mmol) in H2O (8 mL). This mixture was stirred
for 30 min as a white precipitate was formed. The suspension
was diluted with H2O (20 mL), 1 M H3PO4 was added to pH 4,
and the mixture was extrated with CH2Cl2 (3 × 20 mL), dried,
and evaporated. Remaining dioxane was removed by azeo-
tropic distillation with toluene (100 mL), giving 569 mg (94%)
of 9p as an oil which solidified on standing: mp 86-90 °C; 1H
NMR δ 7.89 (d, J ) 8.8, 2H), 7.78 (m, 1H), 7.48 (m, 1H), 6.68
(d, J ) 8.8, 1H), 5.58 (m, 1H), 5.03 (m, 1H), 4.46 (m, 1H), 3.41
(m, 1H), 3.84 (s, 3H), 3.62-3.34 (m, 2H), 2.51 (t, J ) 7.2, 2H),
2.07-1.85 (m, 3H), 2.05 (s, 3H), 1.5-1.45 (m, 2H), 1.41 (s, 9H),
0.92 (m, 6H); 13C NMR δ 197.0, 174.0, 171.9, 170.9, 163.7,
155.6, 130.5, 129.0, 113.6, 80.12, 57.0, 55.4, 53.6, 49.3, 39.7,
ter t-Bu tyl (S)-2-((ter t-Bu toxyca r bon yl)a m in o)-5-[2,2-
(1,3-d ioxola n yl)]-5-(2-m eth oxyp h en yl)p en ta n oa te (12o)
was prepared as described for the para isomer. From 1.1 g
(2.8 mmol) of ketone 11o was obtained 735 mg, 75% yield, of
ketal 12o as an oil: 1H NMR δ 7.42 (dd, J ) 7.8, 1.7, 1H),
7.25 (dd, J ) 15.6, 1.7, 1H), 6.90-6.86 (m, 2H), 5.01 (d, J )
8.2, 1H), 4.09 (m, 1H), 4.00-3.95 (m, 2H), 3.86-3.80 (m, 5H),
2.19-2.10 (m, 1H), 1.91-1.77 (m, 1H), 1.63-1.57 (m, 1H), 1.41
(s, 18H); 13C NMR δ 171.9, 157.1, 155.2, 129.5, 129.1, 127.2,
120.0, 111.8, 109.7, 81.3, 79.2, 64.7, 55.7, 53.7, 33.1, 28.2, 27.9,
26.8; [R]22 -5.1° (c 1, EtOH). Anal. Calcd for C23H35NO7:
D
C, 63.1; H, 8.1; N, 3.2. Found: C, 62.9; H, 7.9; N, 3.1.
ter t-Bu tyl (S)-2-((ter t-Bu toxyca r bon yl)a m in o)-5-[2,2-
(1,3-d ith iola n yl)]-5-(4-m eth oxyp h en yl)p en ta n oa te (13p).
To a stirred solution of ketal 12p (1.53 g, 2.8 mmol) and 1,2-
ethanedithiol (1.64 g, 17.5 mmol) at 0 °C was added BF3‚Et2O
(400 mg, 2.8 mmol) over a 5 min period. The reaction mixture
was stirred for 15 min at 0 °C and then warmed to rt and
stirred for 2 h, diluted with CH2Cl2 (20 mL), and washed with
saturated NaHCO3 (25 mL) and H2O (2 × 25 mL). The organic
layer was dried, filtered, and evaporated. Chromatography
of the residue (EtOAc/hexanes, 1/6) gave thioketal 13p (800
mg, 49%) as a colorless oil. Continued elution with MeOH/
CH2Cl2, 1/20, gave the free amine 14p from which the tert-
butoxycarbonyl group had been cleaved. Reprotection by the
standard procedure gave additional 13p (704 mg, 43%), for a
total yield of 92%: 1H NMR δ 7.56 (d, J ) 8.8, 2H), 6.82 (d, J
) 8.8, 2H), 4.97 (br d, 1H), 4.18-4.12 (m, 1H), 3.79 (s, 3H),
3.40-3.23 (m, 4H), 2.39 (td, J ) 8.3, 4.1, 1H), 2.25 (td, J )
8.3, 4.6, 1H), 1.82-1.78 (m, 1H), 1.66-1.56 (m, 1H), 1.43 (s,
9H), 1.42 (s, 9H); 13C NMR δ 171.3, 158.5, 155.1, 136.3, 129.3,
128.1, 111.3, 81.8, 79.6, 73.0, 55.2, 53.6, 41.2, 39.3, 30.6, 28.1,
37.0, 31.7, 30.0, 28.1, 24.8, 15.4, 15.1, 11.5; [R]22 +31.7° (c 1,
D
CHCl3); HRMS Calcd for C27H42N3O8S (MH+) 568.2692, found
568.2707. Anal. Calcd for C27H41N3O8S: C, 57.1; H, 7.3; N,
7.4. Found: C, 57.5; H, 7.0; N, 7.2.
BOC-Met-An oAsp -Ile-OH (9o) was prepared as described
for the para isomer. From 850 mg, 1.46 mmol, of 8o was
1
obtained 775 mg (93%) of 9o: mp 68-72 °C; H NMR δ 7.73
(d, J ) 7.6, 1H), 7.56 (m, 1H), 7.44 (m, 1H), 7.30 (m, 1H), 6.96-
6.89 (m, 2H), 5.46 (m, 1H), 4.99 (m, 1H), 4.47-4.43 (m, 1H),
3.85 (s, 3H), 3.62-3.41 (m, 2H), 2.51 (t, J ) 7.0, 2H), 2.04 (s,
3H), 2.04-1.89 (m, 3H), 1.48-1.17 (m, 2H), 1.39 (s, 9H), 0.91
(m, 6H); 13C NMR δ 199.6, 174.3, 171.8, 170.9, 159.0, 155.6,
134.4, 130.6, 126.4, 120.5, 111.5, 80.1, 56.9, 55.4, 53.6, 49.4,
45.6, 37.1, 31.7, 30.0, 28.2, 24.8, 15.4, 15.1, 11.6; [R]22D +26.5°
(c 1, CHCl3); HRMS calcd for C27H42N3O8S (MH+) 568.2692,
found 568.2699. Anal. Calcd for C27H41N3O8S: C, 57.1; H,
7.3; N, 7.4. Found: C, 57.1; H, 7.0; N, 6.9.
HCl‚Met-An pAsp -Ile-OCH3 (10p). A 1 M solution of HCl
in ethyl acetate (30 mmol) was added dropwise to a solution
of BOC-Met-AnpAsp-Ile-OCH3 (8p, 790 mg, 1.36 mmol) in ethyl
acetate (7 mL). The solution was stirred for 2 h and then
evaporated, and the residue, after trituration with ether, was
crystallized from methanol/ether to give 597 mg (85%) of 10p:
mp 161-164 °C; 1H NMR (CD3OD) δ 7.96 (d, J ) 8.9 Hz, 2H),
6.99 (d, J ) 8.9 Hz, 2H), 5.01-4.97 (m 1H), 4.35 (d, J ) 5.7
Hz, 1H), 3.93 (t, J ) 6.5 Hz, 1H), 3.85 (s, 3H), 3.66 (s, 3H),
3.49-3.45 (m, 2H), 2.58 (t, J ) 7.8 Hz, 2H), 2.15-2.06 (m, 2H),
2.09 (s, 3H), 1.89-1.85 (m, 1H), 1.48-1.41 (m, 1H), 1.28-1.21
(m, 1H), 0.91-0.88 (m, 6H); 13C NMR (CD3OD) δ 196.5, 173.3,
173.2, 169.6, 165.6, 131.5, 130.5, 114.9, 58.4, 56.1, 53.5, 52.5,
50.9, 40.6, 38.4, 32.3, 29.6, 26.3, 16.0, 15.1, 11.8; [R]25D +11.6°
(c 1, CH3OH). Anal. Calcd for C23H36N3O6SCl: C, 53.3; H,
7.0; N, 8.1. Found: C, 53.6; H, 6.9; N, 7.9.
28.0; [R]22 +6.7° (c 1, EtOH). Anal. Calcd for C23H35NO5S2:
D
C, 58.8; H, 7.5; N, 3.0. Found: C, 59.0; H, 7.5; N, 3.0.
The intermediate N-deprotected amine isolated in the above
ketal to thioketal transformation, ter t-bu tyl (S)-2-a m in o-5-
[2,2-(1,3-d it h iola n yl)]-5-(4-m et h oxyp h en yl)p en t a n oa t e
(14p) was further characterized: 1H NMR δ 7.58 (d, J ) 8.8,
2H), 6.82 (d, J ) 8.8, 2H), 3.79 (s, 3H), 3.41-3.22 (m, 5H),
2.47-2.39 (m, 4H), 1.74-1.65 (m, 1H), 1.63-1.56 (m, 1H), 1.43
(s, 9H); 13C NMR δ 174.6, 158.3, 136.3, 128.1, 113.1, 80.9, 73.1,
55.1, 54.5, 41.6, 39.2, 32.7, 27.9; [R]22D +7.4° (c 1, EtOH). Anal.
Calcd for C18H27NO3S2: C, 58.5; H, 7.4; N, 3.6. Found: C, 58.5;
H, 7.4; N, 3.6.
ter t-Bu t yl (S)-2-((ter t-b u t oxyca r b on yl)a m in o)-5-[2,2-
(1,3-d ith iola n yl)]-5-(2-m eth oxyp h en yl)p en ta n oa te (13o)
was prepared as described for the para isomer. The product,
13o, was obtained as an oil in 90% yield: 1H NMR δ 7.79 (dd,
J ) 8.0, 1H), 7.26-7.21 (m, 1H), 6.91-6.86 (m, 2H), 4.93 (br
d, 1H), 3.88 (s, 3H), 3.33-3.15 (m, 4H), 2.53-2.37 (m, 2H),
1.76-1.53 (m, 2H), 1.42 (s, 9H), 1.41 (s, 9H); 13C NMR δ 171.5,
156.7, 155.0, 132.3, 128.7, 127.8, 120.2, 111.9, 81.5, 79.2, 72.3,
HCl‚Met-An oAsp -Ile-OCH3 (10o) was prepared as de-
scribed for the para isomer. From 315 mg, 0.54 mmol, of 8o
was obtained 262 mg (93%) of 10o: mp 167-169 °C; 1H NMR
(CD3OD) δ 7.77-7.34 (m, 1H), 7.58-7.53 (m, 1H), 7.17-7.14
(m, 1H), 7.05-7.00 (m, 1H), 5.01-4.95 (m, 1H), 4.41-4.36 (m,

720 J . Org. Chem., Vol. 61, No. 2, 1996
Berre´e et al.
55.5, 53.6, 38.8, 38.8, 30.9, 28.3, 27.9; [R]22D +6.0° (c 1, EtOH).
Anal. Calcd for C23H35NO5S2: C, 58.8; H, 7.5; N, 3.0. Found:
C, 58.6; H, 7.7; N, 3.0.
2.20-2.33 (m, 2H), 2.93-3.12 (m, 2H), 3.77 (s, 3H), 3.83 (s,
3H), 4.88 (t, 1H), 6.90 (d, 2H), 7.82 (d, 2H); 13C NMR δ 26.3,
35.2, 52.1, 55.2, 74.2, 113.5, 126.4, 129.6, 161.6, 173.4, 175.1.
Anal. Calcd for C13H15NO3: C, 66.9; H, 6.5; N, 6.0. Found:
C, 66.9; H, 6.4; N, 5.7.
The intermediate N-deprotected amine isolated in the above
ketal to thioketal transformation, ter t-bu tyl (S)-2-a m in o-5-
[2,2-(1,3-d it h iola n yl)]-5-(2-m et h oxyp h en yl)p en t a n oa t e-
(14o), was further characterized: 1H NMR δ 7.79 (dd, J ) 8.0,
1.6, 1H), 7.26-7.21 (m, 1H), 6.91-6.86 (m, 2H), 3.88 (s, 3H),
3.31-3.41 (m, 4H), 2.52 (t, J ) 7.9, 3H), 1.76 (br s, 2H), 1.59-
1.45 (m, 2H), 1.42 (s, 9H); 13C NMR δ 174.8, 156.6, 132.3, 128.6,
127.7, 120.1, 111.8, 80.7, 72.5, 55.5, 54.6, 39.3, 38.7, 33.4, 27.9;
BOC-An pGlu Eth ylen e Dith iok eta l Ile-OCH3 (18p).
Coupling between glutamic acid analogue 16p and isoleucine
methyl ester was carried out as described for the synthesis of
dipeptide 6. From 430 mg, 1.04 mmol, of 16p was obtained
382 mg, 72% yield, of dipeptide 18p: 1H NMR δ 7.51 (d, J )
8.8, 2H), 6.75 (d, J ) 8.8, 2H), 6.48 (br d, 1H), 4.86 (br d, 1H),
4.46 (dd, J ) 4.9, 3.7 1H), 3.96-3.88 (m, 1H), 3.72 (s, 3H),
3.66 (s, 3H), 3.32-3.20 (m, 4H), 2.33-2.30 (m, 2H), 1.88-1.75
(m, 2H), 1.58-1.46 (m, 1H), 1.37 (s, 9H), 1.19-1.12 (m, 2H),
0.85-0.79 (m, 5H); 13C NMR δ 171.9, 171.3, 158.5, 155.6, 136.2,
128.2, 113.3, 80.1, 73.1, 56.4, 55.2, 54.2, 52.0, 41.7, 39.4, 37.7,
[R]22 +10.7° (c 1, EtOH). Anal. Calcd for C18H27NO3S2: C,
D
58.5; H, 7.4; N, 3.8. Found: C, 58.5; H, 7.1; N, 3.8.
(S)-2-Am in o-5-[2,2-(1,3-d ith iola n yl)]-5-(4-m eth oxyp h e-
n yl)p en ta n oic Acid Hyd r och lor id e (15p). To a stirred
solution of N-BOC tert-butyl ester 13p (2.10 g, 4.80 mmol) in
15 mL of CH2Cl2 at 0 °C was added dry HCl dissolved in EtOAc
(5.2 M, 27.7 mL, 144 mmol) over a 10 min period. The reaction
mixture was warmed to rt, stirred for 16 h, filtered, and
washed with EtOAc to give 15p (1.51 g, 90%): mp 175-178
29.8, 28.2, 24.9, 15.3, 11.4; [R]20 -3.0° (c 1, EtOH). Anal.
D
Calcd for C26H40N2O6S2: C, 57.7; H, 7.5; N, 5.2. Found: C,
57.7; H, 7.5; N, 5.1.
BOC-An oGlu eth ylen e d ith iok eta l Ile-OCH3 (18o) was
prepared as described for the para isomer. From 213 mg, 0.52
mmol, of 16o was obtained 170 mg, 61% yield, of 18o: mp 94-
1
°C; H NMR δ (CD3OD) δ 7.58 (d, J ) 8.9, 2H), 6.86 (d, J )
8.9, 2H), 3.93 (t, J ) 6.2, 1H), 3.78 (s, 3H), 3.45-3.28 (m, 4H),
2.61-2.51 (m, 1H), 2.47-2.37 (m, 1H), 2.00-1.80 (m, 2H); 13
C
1
95 °C; H NMR δ 7.74 (dd, J ) 7.6, 1.4, 1H), 7.18 (t, J ) 6.7,
NMR (CD3OD) δ 171.6, 160.4, 137.3, 129.6, 114.5, 73.8, 56.0,
1H), 6.84-6.80 (br d, 1H), 4.87 (br d, 1H), 4.46 (dd, J ) 8.8,
5.0, 1H), 3.90-3.83 (m, 1H), 3.83 (s, 3H), 3.24-3.21 (m, 2H),
3.13-3.10 (m, 2H), 1.85-1.66 (m, 2H), 1.51-1.28 (m, 3H), 1.37
(s, 9H), 1.14-1.03 (m, 1H), 0.84-0.79 (m, 6H); 13C NMR δ
172.1, 171.5, 156.7, 155.6, 132.2, 128.8, 127.8, 120.2, 111.9,
79.9, 72.4, 56.3, 55.5, 54.3, 52.0, 39.3, 38.9, 37.8, 30.9, 29.9,
55.9, 42.4, 40.6, 29.8; [R]22 +26.1° (c 1, EtOH). Anal. Calcd
D
for C14H20NO3S2Cl: C, 48.1; H, 5.7; N, 4.0. Found: C, 48.3;
H, 6.0; N, 3.9.
(S)-2-Am in o-5-[2,2-(1,3d ith iola n yl)]-5-(2-m eth oxyp h e-
n yl)p en ta n oic a cid h yd r och lor id e (15o) was prepared as
described for the para isomer in 86% yield: mp 217-218 °C
dec; 1H NMR (CD3OD) δ 7.78 (dd, J ) 7.8, 1.6, 1H), 7.26 (ddd,
J ) 8.1, 7.5, 1.6, 1H), 6.99 (dd, J ) 8.1, 1.0, 1H), 6.88 (td, J )
7.5, 1.0, 1H), 3.86 (s, 3H), 3.35-3.28 (m, 2H), 3.26-3.16 (m,
2H), 2.64-2.56 (m, 2H), 1.87-1.77 (m, 2H); 13C NMR (CD3-
OD) δ 171.5, 158.3, 133.1, 130.1, 128.7, 121.1, 113.1, 72.9, 56.1,
28.3, 25.0, 15.3, 11.5; [R]20 -5.9° (c 1, EtOH). Anal. Calcd
D
for C26H40N2O6S2: C, 57.7; H, 7.5; N, 5.2. Found: C, 57.7; H,
7.8; N, 5.3.
HCl‚An pGlu Eth ylen e Dith iok eta l Ile-OCH3 (19p). To
a stirred solution of dipeptide 18o (297 mg, 0.57 mmol) in 2
mL of EtOAc at 0 °C was added dry HCl in EtOAc (2.7 M
solution, 3.3 mL, 11.3 mmol) over 5 min. The reaction mixture
was stirred for 3h at rt, methanol (10 mL) was added, and the
solution was evaporated to give the salt 19p (251 mg, 93%) as
an oil: 1H NMR (CD3OD) δ 8.6 (d, 1H), 7.58 (d, 2H), 6.83 (d,
2H), 4.38 (br s, 1H), 3.96 (br s, 1H), 3.76 (s, 3H), 3.72 (s, 3H),
3.45-3.19 (m, 4H), 2.49-2.43 (m, 1H), 1.89 (br s, 2H), 1.51-
1.21 (m, 2H), 0.98-0.93 (m, 6H); 13C NMR (CD3OD) δ 171.5,
171.3, 158.6, 135.5, 128.3, 113.3, 72.3, 57.2, 56.2, 55.7, 53.0,
40.2, 36.9, 36.8, 29.5, 25.3, 15.3, 11.2. Anal. Calcd for
53.7, 39.8, 30.1; [R]22 +45.5° (c 1.3, EtOH). Anal. Calcd for
D
C14H20NO3S2Cl: C, 48.1; H, 5.8; N, 4.0. Found: C, 47.8; H,
5.7; N, 3.9.
(S)-2-((ter t-Bu toxyca r bon yl)a m in o)-5-[2,2-(1,3-d ith iola -
n yl)]-5-(4-m eth oxyp h en yl)p en ta n oic Acid (BOC-An pGlu
Eth ylen e Dith iok eta l, 16p). To a stirred solution of the salt
15p (1.12 g, 3.2 mmol) in THF (10 mL) and H2O (10 mL) were
added (BOC)2O (1.39 g, 6.4 mmol) and Et3N (0.97 g, 9.6 mmol)
at rt. The reaction mixture was stirred for 17 h at rt, EtOAc
(30 mL) was added, and then the aqueous layer was acidified
to pH 2 with 1 M H3PO4. It was extracted with EtOAc (2 ×
30 mL), and the combined organic layers were dried, filtered,
and evaporated. The residue was chromatographed (CH2Cl2/
MeOH, 12/1) to give the acid 16p (1.22 g, 92%): mp 127-130
C
21H33N2O4S2Cl: C, 52.9; H, 7.0; N, 5.9. Found: C, 52.5; H,
7.2; N, 5.7.
HCl‚An pGlu eth ylen e d ith iok eta l Ile-OCH3 (19o) was
prepared as described for the para isomer 19p, except that
the reaction product was purified by chromatography (CH2-
Cl2/MeOH, 12/1). From 130 mg, 0.24 mmol, of BOC-dipeptide
18o was obtained 94 mg, 82% yield, of 19o as an oil: 1H NMR
(CD3OD) δ 7.74 (d, J ) 7.8, 1H), 7.26-7.17 (m, 1H), 6.94 (d, J
) 8.1, 1H), 6.83 (td, J ) 7.5, 1.0, 1H), 4.33 (d, J ) 6.5, 1H),
3.85 (s, 3H), 3.69 (s, 3H), 3.32-3.11 (m, 4H), 2.59-2.41 (m,
2H), 1.91-1.78 (m, 1H), 1.58-1.37 (m, 3H), 1.29-1.12 (m, 1H),
0.91-0.88 (m, 6H); 13C NMR (CD3OD) δ 177.2, 173.2, 158.4,
133.9, 129.8, 128.8, 121.0, 113.2, 73.7, 58.0, 52.5, 40.9, 39.7,
39.6, 38.4, 35.3, 26.3, 16.0, 11.7.
1
°C; H NMR δ 7.56 (d, 2H), 6.82 (d, 2H), 5.01 (br d, 1H), 4.24
(s, 1H), 3.79 (s, 3H), 3.39-3.25 (m, 4H), 2.43-2.35 (m, 2H),
1.93-1.67 (m, 2H), 1.43 (s, 9H); 13C NMR δ 176.5, 158.4, 155.4,
136.1, 128.1, 113.3, 80.0, 72.9, 55.1, 53.1, 41.4, 39.3, 30.3, 28.2.
Anal. Calcd for C19H27NO5S2: C, 55.2; H, 6.6; N, 3.4. Found:
C, 55.0; H, 6.4; N, 3.2.
(S)-2-((ter t-Bu toxyca r bon yl)a m in o)-5-[2,2-(1,3-d ith iola -
n yl)]-5-(2-m eth oxyp h en yl)p en ta n oic a cid (BOC-An oGlu
eth ylen e d ith iok eta l, 16o) was prepared as described for the
1
para isomer in 95% yield: mp 144-145.5 °C; H NMR δ 9.8
(br s, 1H), 7.78 (d, J ) 6.6, 1H), 7.23 (d, J ) 7.8, 1H), 6.88 (t,
J ) 6.9, 2H), 4.86 (d, J ) 7.7, 1H), 4.18-4.12 (m, 1H), 3.86 (s,
3H), 3.30-3.15 (m, 4H), 2.58-2.49 (m, 2H), 1.83-1.72 (m, 1H),
1.58-1.49 (m, 1H), 1.41 (s, 9H); 13C NMR δ 177.5, 156.7, 155.5,
132.1, 128.9, 128.4, 127.8, 120.3, 112.0, 80.1, 72.3, 55.5, 54.3,
53.2, 38.9, 30.5, 28.3; [R]22D +25.0° (c 1.26, EtOH). Anal. Calcd
for C19H27NO5S2: C, 55.2; H, 6.6; N, 3.4. Found: C, 55.0; H,
6.7; N, 3.2.
BOC-Met-An pGlu Eth ylen e Dith iok eta l Ile-OCH3 (20p).
The dipeptide salt 19p (267 mg, 0.55 mmol) and N-methyl-
morpholine (107 mg, 1.06 mmol) in 2 mL of DMF/THF, 1/1,
was coupled with BOC-Met (263 mg, 1.06 mmol) using CBMIT
activation as previously described. The resulting reaction
mixture was stirred for 3h at rt and then diluted with
saturated NaHCO3 (10 mL). The aqueous layer was extracted
with EtOAc (2 × 15 mL), and the combined organic layers were
dried, filtered, and evaporated. The residue was purified by
chromatography (EtOAc/hexanes, 1/1) to give 20p (253 mg,
(S)-2-(Met h oxyca r b on yl)-5-(4-m et h oxyp h en yl)-5-p yr -
r olin e (17p). A solution of ketal 12p (360 mg, 1.1mmol) in 3
mL of 3 M HCl in methanol was stirred for 5 h at rt. The
reaction mixture was then evaporated, the residue was dis-
solved in CH2Cl2 (5mL), triethylamine (0.18 mL, 1.3 mmol)
was added, and the mixture was stirred for 15h at rt. It was
then washed with H2O (2 × 2 mL), dried, and evaporated.
Recrystallization of the residue from EtOAc/hexanes gave
1
70%): mp 151-152 °C; H NMR δ 7.57 (d, 2H), 6.82 (d, 2H),
6.61 (d, 1H), 5.26 (1H), 4.51 (s, 1H), 4.39 (1H), 3.73 (s, 3H),
3.70 (s, 3H), 3.33 (m, 4H), 2.54 (2H), 2.09 (s, 3H), 2.06 (2H),
1.91 (2H), 1.63-1.46 (2H), 1.44 (s, 9H), 1.34 (1H), 1.28 (1H),
1.26 (d, 1H), 0.87 (m, 6H); 13C NMR δ 173.9, 171.9, 170.7,
158.3, 155.3, 135.9, 128.0, 113.1, 79.6, 72.7, 56.3, 54.9, 53.2,
52.6, 51.8, 40.9, 39.2, 37.3, 31.9, 29.8, 28.6, 28.1, 24.8, 15.2,
1
pyrroline 17p, 150 mg, 61% yield: mp 72-73 °C; H NMR δ

Synthesis of Anisolylated Aspartyl and Glutamyl Tripeptides
J . Org. Chem., Vol. 61, No. 2, 1996 721
15.0, 11.2; [R]20D -9.7° (c 1.3, EtOH). Anal. Calcd for C31H49
-
158.9, 155.5, 133.9, 130.5, 127.6, 120.6, 111.6, 80.1, 56.8, 55.5,
53.7, 53.1, 52.1, 40.2, 37.6, 31.9, 30.2, 28.3, 27.2, 25.1, 15.6,
N3O7S3: C, 55.4; H, 7.3; N, 6.2. Found: C, 55.2; H, 7.3; N,
6.1.
15.3, 11.6; [R]20 -21.6° (c 1.2, EtOH). Anal. Calcd for
D
BOC-Met-An oGlu eth ylen e d ith iok eta l Ile-OCH3 (20o)
was prepared by coupling dipeptide 19o with BOC-Met (89
mg, 0.36 mmol) as described for the para isomer. The yield of
tripeptide 20o was 70 mg, 71%: mp 159-161 °C; 1H NMR
(CD3OD) δ 7.78 (dd, J ) 7.7, 1.4, 1H), 7.23 (t, J ) 7.6, 1H),
6.90-6.86 (m, 2H), 6.58 (br d, 1H), 6.47 (br d, 1H), 5.8 (br,
1H), 4.49 (dd, J ) 8.6, 5.0, 1H), 4.28-4.22 (m, 2H), 3.88 (s,
3H), 3.71 (s, 3H), 3.31-3.16 (m, 4H), 2.52-2.46 (m, 4H), 2.07
(s, 3H), 2.06-1.82 (m, 5H), 1.73-1.31 (m, 2H), 1.43 (s, 9H),
1.18-1.05 (m, 1H), 0.88 (t, J ) 3H), 0.84 (d, J ) 7.8); 13C NMR
(CD3OD) δ 219.3, 171.8, 171.5, 170.6, 156.8, 155.4, 132.3, 128.9,
127.8, 120.3, 112.1, 85.3, 80.2, 72.4, 56.5, 55.7, 53.2, 52.1, 39.1,
C29H45N3O8S: C, 58.5; H, 7.6; N, 7.1. Found: C, 58.1; H, 7.5;
N, 6.8.
BOC-Met-An pGlu -Ile-OH (22p). To a stirred solution of
21p (270 mg, 0.45 mmol) in 3 mL of 1,4-dioxane at rt was
added a solution of LiOH‚H2O (74.4 mg, 1.81 mmol) in 3 mL
of H2O, and the reaction mixture was stirred for 35 min at rt.
Water (15 mL) was added, and the aqueous phase was washed
with Et2O (10 mL) and then acidified to pH 3 (0.5M H3PO4)
and extracted with EtOAc (3 × 15 mL). Drying, filtering, and
evaporating the organic phase gave a residue which was
chromatographed (CH2Cl2/MeOH, 12/1) to give 22p (240 mg,
93%) as a foam: 1H NMR δ 7.89 (d, J ) 8.7, 1H), 7.66 (dt, J )
6.1, 1.7, 2H), 7.44-7.39 (m, 1H), 3.82 (s, 3H), 3.22-3.03 (m,
2H), 2.49 (t, J ) 7.2, 2H), 2.92-2.12 (m, 1H), 2.02 (s, 3H),
2.08-2.82 (m, 4H), 1.61-1.32 (m, 1H), 1.39 (s, 9H), 1.26-1.24
(m, 1H), 0.789 (d, J ) 7.4, 3H), 0.74 (t, J ) 7.1, 3H); 13C NMR
δ 198.9, 174.1, 172.3, 171.7, 163.6, 130.6, 129.5, 113.7, 80.1,
57.1, 55.4, 53.8, 52.8, 37.2, 34.2, 32.1, 30.0, 28.3, 27.5, 25.1,
38.9, 38.8, 37.8, 31.9, 30.2, 28.3, 25.1, 15.4, 15.3, 11.5; [R]20
D
-18.6° (c 1, EtOH). Anal. Calcd for C31H49N3O7S3: C, 55.4;
H, 7.3; N, 6.2. Found: C, 55.2; H, 7.6; N, 6.1.
BOC-Met-An pGlu -Ile-OCH3 (21p). To a stirred solution
of 20p (145 mg, 0.22 mmol) in 8.5 mL of CHCl3 at rt was added
a solution of Hg(C1O4)2‚3H2O (200 mg, 0.44 mmol) in 5 mL of
MeOH over 3 min. The reaction mixture was stirred for 1.5h
at rt and then filtered and basified with 10% K2CO3. The
concentrated filtrate was extracted with CHCl3 (2 × 10 mL),
and the combined organic layer was washed with brine (10
mL), dried, filtered, and evaporated. Chromatography of the
residue (EtOAc/hexane, 1/2) gave 21p (112 mg, 85%): mp 86-
88 °C; 1H NMR δ 7.88 (d, J ) 8.8, 2H), 7.19 (d, J ) 11.4, 2H),
6.85 (d, J ) 8.8, 2H), 5.19 (d, J ) 8.0, 1H), 4.49-4.42 (m, 2H),
4.24-4.17 (1H), 3.80 (s, 3H), 3.65 (s, 3H), 3.28-3.17 (m, 1H),
2.06-1.97 (m, 1H), 2.00 (s, 3H), 1.92-1.79 (m, 2H), 1.35 (s,
9H), 1.19-1.11 (m, 1H), 0.86-0.82 (m, 6H); 13C NMR δ 198.8,
172.0, 171.6, 171.1, 163.7, 130.5, 129.6, 113.7, 80.1, 56.8, 55.4,
53.7, 52.8, 37.4, 34.5, 31.8, 30.1, 28.2, 25.1, 15.5, 15.2, 11.5;
[R]20D -11.8° (c 0.9, EtOH). Anal. Calcd for C29H45N3O8S: C,
58.5; H, 7.6; N, 7.1. Found: C, 58.3; H, 7.5; N, 6.9.
15.5, 15.3, 11.6; [R]20 -10.8° (c 0.8, EtOH). HRMS calcd for
D
C28H44N3O8S (MH+) 582.2849, found 582.2847. Anal. Calcd
for C28H43N3O8S: C, 57.8; H, 7.4; N, 7.2. Found: C, 57.4; H,
7.6; N, 7.0.
BOC-Met-An oGlu -Ile-OH (22o) was prepared as described
for the para isomer. From 240 mg, 0.4 mmol, of methyl ester
21o was obtained 218 mg, 93% yield, of acid 22o as an
amorphous solid: 1H NMR δ 7.71 (dd, J ) 7.7, 1H), 7.61 (br
d, 1H), 7.47-7.42 (m, 2H), 7.42 (br d, 1H), 6.96 (q, J ) 7.4,
2H), 5.50 (d, J ) 7.2, H), 4.60-4.52 (m, 2H), 4.30 (br, 1H),
3.87 (s, 3H), 3.26-3.06 (m, 2H), 2.52 (t, J ) 7.3, 2H), 2.24-
2.19 (m, 1H), 2.05 (s, 3H), 1.93-1.86 (m, 4H), 1.51-1.47 (m,
1H), 1.40 (s, 9H), 1.30-1.18 (m, 1H), 0.96-0.89 (m, 6H); 13C
NMR δ 202.5, 174.0, 172.2, 171.7, 158.9, 155.7, 133.9, 130.5,
127.5, 120.6, 111.7, 80.2, 57.1, 55.5, 53.9, 53.2, 40.0, 37.2, 32.0,
BOC-Met-An oGlu -Ile-OCH3 (21o) was prepared as de-
scribed for the para isomer. From 840 mg, 1.25 mmol, of 20o
30.1, 28.3, 27.1, 25.1, 15.5, 15.3, 11.6; [R]20 -16.9° (c 1.9,
D
EtOH); HRMS calcd for C28H44N3O8S (MH+) 582.2849, found
582.2843. Anal. Calcd for C28H43N3O8S: C, 57.8; H, 7.4; N,
7.2. Found: C, 58.0; H, 7.7; N, 6.9.
1
was obtained 658 mg, 88% yield, of 21o: mp 124-125 °C; H
NMR δ 7.67 (dd, J ) 7.7, 1.8, 1H), 7.09 (d, J ) 6.8, 1H), 7.02
(d, J ) 8.4, 1H), 6.92 (q, J ) 8.3, 2H), 5.15 (br d, 1H), 4.49-
4.40 (m, 2H), 4.13-4.25 (m, 1H), 3.83 (s, 3H), 3.64 (s, 3H),
3.31-2.98 (m, 2H), 2.48 (t, J ) 7.3, 2H), 2.27-1.70 (m, 6H),
2.02 (s, 3H), 1.41-1.30 (m, 2H), 1.35 (s, 9H), 1.22-1.05 (m,
2H), 0.87-0.82 (m, 6H); 13C NMR δ 202.4, 172.0, 171.6, 171.2,
Ack n ow led gm en t. A.C. thanks the Xunta de Gali-
cia and NATO for fellowship support.
J O951754C