Synthesis of a trisubstituted 1,4-diazepin-3-one-based dipeptidomimetic as a novel molecular scaffold

Article abstract of DOI:10.1021/jo962257e

We describe two routes for the synthesis of a trisubstituted 1,2,5-hexahydro-3-oxo-1H-1,4-diazepine ring (DAP), a novel, conformationally constrained, seven-membered dipeptidomimetic ring system. The linear precursor for the model DAPs, targeted for conformational analysis studies, was obtained by reductive alkylation of tert-butyl alaninate or phenylalaninate by N-Boc-α-amino-γ-oxo-N,N-dimethylbutyramide. Acetylation of the newly formed secondary amine followed by acidolytic deprotection of the amino and carboxyl terminal protecting groups and subsequent diphenylphosphorazidate-mediated ring formation yielded the blocked model DAPs. The synthesis of the DAP synthon started with 1-tert-butyl hydrogen N-(benzyloxycarbonyl)aspartate. The aldehyde obtained from the β-carboxyl was used to reductively alkylate benzyl phenylalaninate, generating a secondary amine. Hydrogenolytic deprotection of the end-groups yielded the linear precursor which was cyclized via lactam formation mediated by 1-hydroxy-7-azabenzotriazolyl-N,N,N',N'-tetramethyluronium hexafluorophosphate. This route yielded the reversibly protected hexahydro-1H-3-oxo-2(S)-benzyl-5(S)-(tert-butyloxycarbonyl)-1,4-diazep ine. This synthon unit can be subsequently elaborated by substituting the functional groups (secondary amine and carboxyl). Therefore, the DAPs may serve as novel molecular scaffolds to reproduce a biologically relevant topology or as a dipeptido-conformation-mimetic that can be incorporated into bioactive peptides. In addition, these synthetic routes will allow the introduction of different chiralities at positions 2 and 5 as well as the diversification of the side chains at position 2. Furthermore, the synthetic routes described here can be easily modified to obtain larger ring systems with variable degrees of conformational flexibility.

Full text of DOI:10.1021/jo962257e

J . Org. Chem. 1997, 62, 2527-2534
2527
Syn th esis of a Tr isu bstitu ted 1,4-Dia zep in -3-on e-Ba sed
Dip ep tid om im etic a s a Novel Molecu la r Sca ffold
Iris S. Weitz,†,‡ Maria Pellegrini,§ Dale F. Mierke,§ and Michael Chorev*,‡,|
Department of Pharmaceutical Chemistry, School of Pharmacy, Faculty of Medicine,
The Hebrew University of J erusalem, J erusalem 91120, Israel, Carlson School of Chemistry,
Clark University, 950 Main Street, Worcester, Massachusetts 01610, and Division of Bone & Mineral
Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School,
330 Brookline Avenue (HIM 944), Boston, Massachusetts 02215
Received December 3, 1996X
We describe two routes for the synthesis of a trisubstituted 1,2,5-hexahydro-3-oxo-1H-1,4-diazepine
ring (DAP), a novel, conformationally constrained, seven-membered dipeptidomimetic ring system.
The linear precursor for the model DAPs, targeted for conformational analysis studies, was obtained
by reductive alkylation of tert-butyl alaninate or phenylalaninate by N-Boc-R-amino-γ-oxo-N,N-
dimethylbutyramide. Acetylation of the newly formed secondary amine followed by acidolytic
deprotection of the amino and carboxyl terminal protecting groups and subsequent diphenylphos-
phorazidate-mediated ring formation yielded the blocked model DAPs. The synthesis of the DAP
synthon started with 1-tert-butyl hydrogen N-(benzyloxycarbonyl)aspartate. The aldehyde obtained
from the â-carboxyl was used to reductively alkylate benzyl phenylalaninate, generating a secondary
amine. Hydrogenolytic deprotection of the end-groups yielded the linear precursor which was
cyclized via lactam formation mediated by 1-hydroxy-7-azabenzotriazolyl-N,N,N′,N′-tetramethyl-
uronium hexafluorophosphate. This route yielded the reversibly protected hexahydro-1H-3-oxo-
2(S)-benzyl-5(S)-(tert-butyloxycarbonyl)-1,4-diazepine. This synthon unit can be subsequently
elaborated by substituting the functional groups (secondary amine and carboxyl). Therefore, the
DAPs may serve as novel molecular scaffolds to reproduce a biologically relevant topology or as a
dipeptido-conformation-mimetic that can be incorporated into bioactive peptides. In addition, these
synthetic routes will allow the introduction of different chiralities at positions 2 and 5 as well as
the diversification of the side chains at position 2. Furthermore, the synthetic routes described
here can be easily modified to obtain larger ring systems with variable degrees of conformational
flexibility.
In tr od u ction
In an effort to stabilize a putative bioactive conforma-
tion, conformational constraints are frequently employed.
Global reduction in the conformational degrees of free-
dom of linear peptides is achieved by a variety of long-
and medium-range homodetic and heterodetic cycliza-
tions.14-17 In addition, local constraints are accomplished
by short-range cyclizations generated through bridging
neighboring amino acid residues via small ring
formation.17-21 For example, γ-lactams18 and pipera-
zinone19-21 rings are obtained by bridging either CRi-to-
Ni+1 or Ni-to-Ni+1, respectively.
Drugs based on peptides such as insulin, calcitonin,
adrenocorticotropin, vasopressin, gonadotropin-releasing
hormone, somatostatin, glucagon and thyrotropin-releas-
ing hormone are used as prescription medications in
treatment of various disease. Nevertheless, in search for
increased specificity and improved pharmacokinetics and
pharmacodynamics, great efforts in peptide-based drug
design are being made in the development of a wide-
range of nonpeptidic structural modifications. These
include pseudopeptides,1-3 peptidomimetics,4-7 conforma-
tion-mimetics8,9 and mass-screening-derived nonpep-
tides.10-13
A major objective in the development of low molecular
weight, nonpeptidic peptidomimetics is the close repro-
duction of the so-called “bioactive topology” which is
derived from the putative “bioactive conformation”. Small,
* Author to whom correspondence should be addressed.
† This work is presented as partial fulfillment of the requirement
toward a Ph.D. thesis.
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‡ The Hebrew University of J erusalem.
§ Clark University.
| Harvard Medical School.
X Abstract published in Advance ACS Abstracts, April 1, 1997.
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2528 J . Org. Chem., Vol. 62, No. 8, 1997
Weitz et al.
Sch em e 1. 1,2,5-Tr isu bstitu ted
polyfunctional, conformationally constrained, mono- or
polycyclic “molecular scaffolds” which can be substituted
by the essential pharmacophores are ideal for this
transformation.4,22-35 To date, the 1,4-benzodiazepin-3-
one system has been the most widely used “molecular
scaffold”.24-35 Changing the appropriate pharmacophores
yielded potent and selective CCK-A receptor antag-
onists,25-29 CCK-B and gastrin receptor antagonists,28,29
a κ1-opiate receptor agonist,24 GPIIb/IIIa receptor antago-
nists,30,31 a HIV Tat receptor antagonist,32 a inhibitor of
Ras farnesylation,33,34 and inhibitors of HIV reverse
transcriptase.35
Hexa h yd r o-3-oxo-1H-1,4-d iza ep in e (DAP ) a n d
Str u ctu r a lly Rela ted System s
Sch em e 2. Retr osyn th esis of a DAP System
We report here the synthesis of trisubstituted 1,2,5-
hexahydro-3-oxo-1H-1,4-diazepine (DAP) (I) (Scheme 1)
a novel “molecular scaffold” structurally related to the
1,4-benzodiazepin-2-one (II) (Scheme 1). It is a mono-
heterocycle lacking the fused benzene ring included in
the 1,4-benzodiazepin-2-one system.
Interestingly, liposidomycin B and C are lipid-bearing
nucleoside antibiotics which contain a structurally re-
lated 1,4-diazepan-3-one ring system (III) (Scheme 1).36,37
Recently, the diazepanone ring was synthesized as part
of the total synthesis of liposidomycins.38-41
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The DAP system is comprised of two chiral centers,
C-2 and C-5, and three potential substitution sites: a side
chain on C-2, the N-1 as a secondary amine, and the
carboxyl group on C-5. This rigidified dipeptidomimetic
system may function as a “conformation mimetic”, intro-
ducing local conformational constraints, or as a “molec-
ular scaffold” to maintain a defined topology. One can
also realize the potential of this system as a novel
“diversomer” in randomized combinatorial “analogous”
libraries.42 Therefore, the DAP system offers new op-
portunities in bridging the gap between bioactive pep-
tides and peptidomimetic drugs4 and is an important
addition to the arsenal of tools available for rational drug
design.
Resu lts a n d Discu ssion
Syn th esis of Mod el DAP s. The side-chain-to-back-
bone bridging between CRi and Ni-1 in a dipeptidic unit
to generate a seven-membered ring (Scheme 1, I), de-
tailed in this report, is a novel approach for introducing
local conformational constraint. Our retrosynthetic analy-
sis, outlined in Scheme 2, requires the construction of a
linear precursor, generated by a reductive alkylating
step, which will undergo cyclization to form the seven-
membered lactam. The synthetic design is based on the
utilization of the expansive range of commercially avail-
able protected, coded and noncoded, amino acid deriva-
tives as building blocks for the assembly of the trisub-
stituted 1,2,5-hexahydro-3-oxo-1H-1,4-diazepine (DAP).
In addition to the predefined chiralities of the CRs, one
can diversify the structure by introducing a wide range
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3-Oxo-1H-1,4-diazepine-Based Peptidomimetic
J . Org. Chem., Vol. 62, No. 8, 1997 2529
Sch em e 3. Dia ster eom er ic P a ir s of DAP Mod el
Com p ou n d s a n d Th eir Lin ea r P r ecu r sor s
Schemes 3 and 4), generated by the cis-trans isomer-
ization around the acetylated tertiary amide bond, which
1
reveals itself in the H-NMR as two sets of extensively
overlapping signals.
Cyclization of the deprotected linear precursors was
carried out in DMF at high dilution and was mediated
by diphenyl phosphorazidate (DPPA) in the presence of
NaHCO3.46 This procedure resulted in better yields of
the DAP model systems (5SS-F , 5RS-F , 5SS-A and 5RS-
A, see Scheme 3) than cyclization mediated by (benzo-
triazol-1-yloxy)tris(dimethylamino)phosphonium hexaflu-
orophosphate (BOP) in the presence of DIPEA.46 In the
latter case, monitoring the reaction by analytical RP-
HPLC revealed presence of starting material even after
three days.
NMR ch a r a cter iza tion of th e fou r m od el DAP
a n a logs, 5SS-F /A a n d 5RS-F /A. The protons of the
DAP analogs were assigned through 2D, homonuclear,
1H-1H, DQF COSY, and TOCSY experiments, which
display spin-spin coupling (3J H-H) of the protons, and
ROESY and NOESY spectra, which illustrate the dipole-
dipole interactions between pairs of protons closer than
5.0 Å from one another. The HMQC then allowed for
the assignment of all the carbons with directly attached
protons. The HMBC experiment, which illustrates long-
of substituents on C-2, as well as expand the ring size
by employing amino acid residues with longer side chains
in position i (see I, Scheme 1).
1
range H-13C (3J H-C) couplings, allowed for the correla-
The synthesis of the model DAP systems 5SS- and
5RS-F /A (Scheme 3) was based on the readily available
N-protected homoserine lactone (1S) which functions as
an in situ-activated precursor. Dimethylamine-mediated
ring opening generates a primary alcohol which can be
directly oxidized to the corresponding aldehyde (Scheme
4). Blocking the carboxyl of the homoserine as an N,N-
dimethylcarboxamide eliminated the favored and spon-
taneous γ-lactonization. Acetylation of the newly formed
secondary amine (Ni-1) prevented potential side reactions
during the lactamization step. The conformational equiva-
lence of enantiomers RS to SR and SS to RR reduced
the synthetic effort to a single representative of each pair,
namely, 5SS-F /A and 5RS-F /A. The choice of alanyl and
phenylalanyl as the (i - 1) amino acid residues (see I,
Scheme 1) incorporated into the model DAP compounds
was aimed to compare the effect of a methyl versus a
benzyl side chain on conformational preferences of this
system.43
Oxidation of the methylol (2S) to the corresponding
aldehyde was carried out by pyridinium chlorochromate
(PCC) in the presence of silica gel.44 Monitoring the
progress of the oxidation by RP-HPLC reveals the forma-
tion of a more hydrophilic minor side product. Amino
acid analysis and FAB-MS (not shown) suggest the
formation of an ester generated by the condensation of
the â-carboxyl in Boc-Asp-NMe2 (formed by overoxidation
of the aldehyde) with the methylol of Boc-Hse-NMe2 (2S).
We preferred to carry out the more demanding reduc-
tive alkylation first. The preformed N-protected R-amino-
γ-oxo-N,N-dimethylbutyramide, the (i) amino acid resi-
due, was reductively alkylated45 by the free R-amino
function of the (i - 1) amino acid residue prior to the
lactam formation (Scheme 4). Acetylation of the newly
formed secondary amines (3SS-F , 3R S-F , 3SS-A, and
3RS-A, Schemes 3 and 4) results in a mixture of isomers
(in each of the 4SS-F , 4RS-F , 4SS-A, and 4RS-A, see
tion of all the protons with carbon atoms three bonds
removed. Therefore, the constitution of the molecule, the
presence of all of the covalent bonds, was unambiguously
proven. The 13C assignments are an important confirma-
tion of the 1H alignments obtained from the homonuclear
experiments described above. In addition, the HMBC
experiment allowed for the diastereotopic assignment of
the methylene protons of the ring system and the
methylene of phenylalanine. In both diastereomeric
pairs (5SS and 5RS) cis isomer (around the Ac-N-1) is
the predominant one. These assignments were impor-
tant for the conformational investigation of the fully
blocked DAP system (N-1 acetylated and C-5 N,N-
dimethylcarboxy amidated) as described in detail else-
where.43
Syn th esis of a DAP Syn th on . To be widely used as
a dipeptidomimetic unit or as a molecular scaffold, a
protected DAP synthon that can be readily incorporated
into peptides or substituted selectively by pharmaco-
phores of choice is required. Therefore, an alternative
synthetic route was developed to generate a protected
DAP synthon that could serve as a building block
(Scheme 5). Orthogonally protected and commercially
available, 1-tert-butyl hydrogen N-(benzyloxycarbonyl)-
L-aspartate (Z-L-Asp-O-t-Bu) (6) was used as the starting
material. The bulky tert-butyl ester blocks the spontane-
ous lactonization of the N-protected L-homoserine ester
7, obtained upon NaBH4-mediated reduction of the mixed
carbonic-carboxyl acids anhydride, generated in situ.
Oxidation of the methylol moiety to the corresponding
aldehyde and the subsequent reductive alkylation to yield
the secondary amine 8 were carried out in an identical
manner as previously described for the DAP model
compounds (5SS-F /A and 5RS-F /A). In an attempt to
develop a more general synthesis of DAP synthons, we
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2530 J . Org. Chem., Vol. 62, No. 8, 1997
Sch em e 4. Rep r esen ta tive Syn th esis of th e Mod el DAP Com p ou n d 5SS-F
Weitz et al.
Sch em e 5. Syn th esis of th e DAP Syn th on 10
avoided the introduction of a third protecting group, on
the secondary amino function, orthogonal to the N-
benzyloxycarbonyl and the O-tert-butyl ester. This third
orthogonal protecting group will be necessary for the
cases in which the i - 1 amino acid residue possesses a
side chain with a functional group that requires protec-
tion. Apparently, the new secondary amine is neither
reactive enough47 nor favorably positioned to compete
with the cyclization that generates the targeted DAP
system.
nium hexafluorophosphate (HATU)49 in highly diluted
solution of DMF. Interestingly, DPPA was less effective
than HATU as a cyclization reagent. The absence of a
protecting group on the secondary amine and the pres-
ence of a bulky tert-butyl ester group in 9 may explain
the lower yields of 10 as compared to the similar DPPA-
mediated cyclization leading to 5, the model DAPs.
These structural differences may result in the very slow
cyclization rate in the presence of DPPA and the appear-
ance of several side products (as observed by analytical
RP-HPLC, not shown).
Two of the syntheses of the closely related 1,4-diaz-
epan-3-one system (III, Scheme 1) employed reductive
cyclization as the last step.38,39 A more recent synthetic
route41 utilized a similar approach to those reported by
us. In their synthesis the secondary amine is formed by
nucleophilic opening of an epoxide ring by sarcosine
methyl ester. Deprotection followed by condensation
cyclization yields the anticipated III in a significantly
shorter and more efficient synthetic route than previously
reported.38,39
Catalytic transfer hydrogenation48 removed the N-
benzyloxycarbonyl and the benzyl ester from fully pro-
tected compound 8 and yielded the partially protected
linear precursor 9 as an acetate salt. The latter was
transformed into a trifluoroacetate by several lyophiliza-
tion cycles of a diluted trifluroacetic acid solution. The
cyclization of the trifluoroacetate 9 to obtain the tert-butyl
ester of the DAP synthon 10 was achieved with 1-hy-
droxy-7-azabenzotriazolyl-N,N,N′,N′-tetramethyluro-
(47) (a) Sasaki, Y.; Coy, D. H. Peptides 1987, 8, 119. (b) Ron, D.;
Laufer, R.; Frey, J .; Gilon, C.; Selinger, Z.; Chorev, M. In Substance P
and Neurokinins; Henry, J . L., Coutre, R., Cuello, A. C., Pelletier, G.,
Quirion, R., Regoli, D., Eds.; Springer-Verlag: New York, 1987; pp
144-145.
Interestingly, one of our initial attempts to synthesize
the model DAP compounds involved an intramolecular
(48) Anwer, M. K.; Spatola, A. F. Synthesis 1980, 929.
(49) Carpino, L. A. J . Am. Chem. Soc. 1993, 115, 4397.

3-Oxo-1H-1,4-diazepine-Based Peptidomimetic
J . Org. Chem., Vol. 62, No. 8, 1997 2531
grade and were used as received. Catalytic hydrogenations
were carried out in the presence of 10% Pd/C (Merck).
N-alkylation of a urethane NH by the sulfonium methio-
dide Met(S+Me)I- in Boc-Phe-Met[(S+Me)I-]-NMe2; this
scheme failed because of a favorable cyclopropyl ring
formation (data not shown).50 A similar approach when
applied to the synthesis of the 1,4-diazepan-3-one system
(III, Scheme 1) led to an azetidine ring formation.41
N-Boc-L-h om oser in e La cton e (1S). An ice-cold suspen-
sion of L-homoserine lactone HCl (Sigma) (4.68 g, 34 mmol) in
DMF (57 mL) was treated with triethylamine (TEA) (5.1 mL.
37 mmol) and di-tert-butyl dicarbonate (Boc2O) (8.7 mL, 41
mmol), and allowed to warm-up to room temperature (rt).
Upon completion of reaction (determined by negative fluores-
camine test), the solvent was removed in vacuo and the residue
was taken-up in DCM (200 mL) and washed consecutively with
1 N KHSO4 (3 × 200 mL) and brine (1 × 200 mL). The organic
phase was dried over MgSO4 and the solvent removed in vacuo.
Recrystallization of the solid residue from EtOAc/petroleum
ether afforded 5.19 g of a white powder (76% yield): Rf ) 0.71
(acetone-petroleum ether / 1:1); mp 125-126 °C (lit. 125-
126.5 °C51 ); 1H NMR (300 MHz, CDCl3) δ 5.01 (1H, brs), 4.44
(1H, dt J ) 0.9, 9.00 Hz), 4.35 (1H, brs), 4.24 (1H, ddd J )
11.4, 9.3, 5.7 Hz), 2.74 (1H, m), 2.19 (1H, m), 1.45 (9H, s). Anal.
Calcd for C9H15N1O4: C, 53.72; H, 7.51; N, 6.96. Found: C,
53.52; H, 7.59; N, 7.10.
Con clu sion
We report the synthesis of a trisubstituted 1,2,5-
hexahydro-3-oxo-1H-1,4-diazepine (DAP) system, starting
from readily available amino acid derivatives to obtain
fully blocked model diastereomers (5SS-F /A and 5RS-
F /A) and a representative synthon 10. The synthetic
scheme developed for the synthon is general and could
be conveniently applied to construct higher homologs of
the DAP system in which the Ci-to-Ni-1 bridging chain
could be larger than the currently present ethylene
moiety. The representative synthon is designed to be
used as a novel molecular scaffold, presenting the sub-
stituting pharmacophores in a specific molecular topol-
ogy, or as a novel dipeptido-conformation-mimetic unit,
which can be readily incorporated into peptides. The
potential chiral and substitutional diversification fea-
tured in the DAP system offers novel opportunities in
peptidomimetic drug design.
2(S )-[(Bu t yloxyca r b on yl)a m in o]-4-h yd r oxy-N ,N -d i-
m eth ylbu tyr a m id e (2S). To a solution of N-(tert-butyloxy-
carbonyl)-L-homoserine lactone (1S) (3.22 g, 16 mmol) in dry
THF (80 mL) (Aldrich) was added 33% (v/v) dimethylamine
in ethanol (8.6 mL, 48 mmol). After stirring over night at rt
the solvents were removed in vacuo, and the product was dried
over P2O5 to give 3.94 g of a clear oil (100% yield): Rf ) 0.41
1
(acetone - petroleum ether/1:1); H NMR (300 MHz, CDCl3)
δ 5.70 (1H, d, J ) 9.0 Hz, NH), 4.72 (1H, ddd, J ) 9.0, 3.0,
12.0 Hz, CH), 3.68 (3H, m, CH2CH2OH, OH), 3.05 (3H, s,
CH3N), 2.94 (3H, s, CH3N), 1.89 (1H, m, CH2CH2OH), 1.45 (1H,
m, CH2CH2OH), 1.42 (9H, s, CH3 t-Bu). 13C NMR (300 MHz,
CDCl3) δ 172.6 (CO), 157.5 (CO), 80.8 (C-t-Bu), 58.6 (CH2CH2-
OH), 47.9 (CH), 37.7 (NCH3), 37.0 (CHCH2), 36.4 (NCH3), 29.0
(CH3t-Bu). Anal. Calcd for C11H22N2O4: C, 53.64; H, 9.00; N,
11.37. Found: C, 53.70; H, 9.14; N, 11.24.
Exp er im en ta l Section
Gen er a l Meth od s. Thin layer chromatography (TLC) was
performed on plates coated with a 0.20 mm thickness of silica
gel 60 F-254 (Merck). Visualization was accomplished by UV
light, 4% (w/v) ninhydrin in ethanol, 0.1% (w/v) fluorescamine
in acetone, or in the presence of iodine vapors. Gravity column
chromatography was carried out on silica gel 60 (70-230 mesh)
columns (2.5 × 35 cm) (Merck). Final organic solutions were
dried over MgSO4, filtered, and rotary evaporated in vacuo.
Analytical reversed-phase high performance liquid chroma-
tography (RP-HPLC) was carried out on a Lichrospher 100 RP-
18 column (5 µm, 4 × 250 mm) (Merck) at a flow-rate of 1
mL/min. Semipreparative RP-HPLC was carried out on either
µBondapak RP-18 column (10 µm, 19 × 150 mm) (Waters) or
Vydac 300 Å C-18 (10 µm, 22 × 250 mm) at a flow-rate 6 mL/
min. The solvent system used in RP-HPLC included the
following: solvent A, 0.1% (v/v) TFA in CH3CN; solvent B, 0.1%
(v/v) TFA in H2O. The effluent was monitored at 220 nm. 1H-
and 13C-NMR spectra were collected at 300, 400, and 500 MHz
instruments. Chemical shifts (δ) are reported in ppm. 1H
resonances were calibrated using the 7.24 ppm CDCl3 or 4.8
2(S)-[(ter t-Bu tyloxyca r bon yl)a m in o]-4-[[2-p h en yl-1(S)-
(ter t-b u t yloxyca r b on yl)et h yl]a m in o]-N,N-d im et h ylb u -
tyr a m id e (3SS-F ). A solution of the alcohol (2S) (0.99 g, 4
mmol) in dry DCM (10 mL) was added to a suspension of
pyridinium chlorochromate (PCC) (3.45 g, 16 mmol) and silica
gel 60 (70-230 mesh, 3.45 g) in dry DCM (10 mL). The
reaction was monitored by TLC Rf ) 0.59 (acetone-petroleum
ether/1:1) and terminated after 2.5 h by the addition of diethyl
ether (20 mL). The reaction mixture was filtered through a
Celite bed, and the filtrate was concentrated in vacuo to afford
the crude aldehyde which was carried to the next step without
further purification.
To a mixture of a solution of the crude N,N-dimethyl-2(S)-
[(butyloxycarbonyl)amino]-4-oxobutyramide in 1% (v/v) AcOH
in MeOH (7 mL) and molecular sieves Type 3Α (8-12 mesh)
pellets (Aldrich) (∼2 g) was added a solution of tert-butyl
L-phenylalaninate hydrochloride (0.36 g, 1.4 mmol) in MeOH
(2 mL). After 5 min, NaCNBH3 (0.19 g, 3.0 mmol) was added
in two aliquots. After 3 h of stirring at rt the reaction mixture
was filtered, and the filtrate was concentrated in vacuo. The
residue was treated with saturated solution of NaHCO3 (75
mL) and extracted with ether (4 × 75 mL). The combined
ethereal extracts were dried over MgSO4, and the solvent was
removed in vacuo. Gravity column chromatography on silica
gel 60 eluting with a step gradient of 20-33% (v/v) acetone in
petroleum ether afforded 0.34 g of a clear oil as a product (54%
yield, based on tert-butyl phenylalaninate hydrochloride): Rf
ppm D2O resonances of the solvents as internal standards. 13
C
resonances were referenced using the CDCl3 resonance of the
solvent (77 ppm) as an internal standard unless noted other-
wise. The coupling constants in hertz were measured from
one-dimensional spectra unless otherwise stated. The chemi-
cal shift assignment was carried out by double-quantum
filtered correlation (DQFCOSY) and heteronuclear correlation
(HMQC, HMBC) experiments unless otherwise stated. Melt-
ing points were determined with a capillary melting point
apparatus and are uncorrected. Elementary microchemical
analysis was carried out by Dr. S. Blum at the Microanalytical
Laboratory of Organic Chemistry Department in the Hebrew
University. Analytical results were within 0.3% of the theo-
retical values. Mass spectroscopy was performed at the Mass
Spectra Laboratory of Chemistry Department at the Harvard
University (Cambridge, MA), using a FAB ion source.
) 0.35 (acetone - petroleum ether/1:3); k′ ) 5.3 (30-75% (v/
1
v) A in B in 30 min); [R]25 ) -1.2 (c ) 1.295, methanol); H
D
NMR (400 MHz, CDCl3) δ 7.29-7.19 (5H, m, Ar), 5.48 (1H, d,
J ) 8.4 Hz, NH carbamate), 4.70 (1H, dd, J ) 8.4, 13.2 Hz,
CH2CH2CH), 3.33 (1H, t, J ) 7.2 Hz, CHCH2Ph), 2.95 (3H, s,
CH3N), 2.93 (3H, s, CH3N), 2.86 (2H, dd, J ) 7.2, 2.0 Hz,
CHCH2Ph), 2.76 (1H, m, CH2CH2CH), 2.42 (1H, m, CH2CH2-
CH), 1.72 (1H, m, CH2CH2CH), 1.61 (1H, m, CH2CH2CH), 1.46
(9H, s, CH3 t-Bu), 1.36 (9H, s, CH3 t-Bu). 13C NMR (400 MHz,
CDCl3) δ 174.6 (CO), 173.0 (CO), 156.2 (CO), 138.4 (C Ar),
N,N′-Dimethylformamide (DMF) was distilled under re-
duced pressure over ninhydrin. EtOAc was distilled over
CaCl2, and dichloromethane (DCM) was distilled over sodium
wire. Other commercially available chemicals are of the best
(50) Rich, D. H.; Tam, J . P. Synthesis 1978, 46.
(51) Baldwin, J . E.; Flinn, A. Tetrahedron. Lett. 1987, 28, 3605.

2532 J . Org. Chem., Vol. 62, No. 8, 1997
Weitz et al.
130.1 (CH Ar), 128.9 (CH Ar), 127.1 (CH Ar), 81.8 (C-t-Bu),
80.1 (C-t-Bu), 64.4 (CHCH2Ph), 49.0 (CH2CH2CH), 44.4 (CH2-
CH2CH) 40.6 (CHCH2Ph), 37.5 (CH3N), 36.3 (CH3N), 34.6
(CH2CH2CH), 29.1 (CH3 t-Bu), 28.7 (CH3 t-Bu); FAB-MS Calcd
for C24H39N3O5: 449.592, found: m/z ) 450 (M + H)+. Anal.
Calcd for C24H39N3O5·H2O: C, 61.65; H, 8.84; N, 8.99. Found:
C, 61.87; H, 9.00; N, 9.12.
0.32 mmol) in CHCl3 (1.35 mL) was treated with N,N-
diisopropylethylamine (DIPEA) (56 µL, 0.32 mmol), Ac2O (60
µL, 0.64 mmol) and 4-(N,N-dimethylamino)pyridine (DMAP)
(78 mg, 0.32 mmol) and was left to stir overnight. The residue
obtained following removal of solvent in vacuo was dissolved
in EtOAc (70 mL), and washed successively with cold 1 N
KHSO4 (3 × 50 mL), 5%(w/v) NaHCO3 (3 × 50 mL), and brine
(2 × 50 mL), and dried over MgSO4, and the solvent was
removed in vacuo to afford a yellow oil: (130 mg, 83% yield);
k′ ) 6.4 (30-75% (v/v) A in B in 30 min); FAB-MS calcd for
C26H41N3O6: 491.629, found: m/z ) 492 (M + H)+. Anal.
Calcd for C26H41N3O6: C, 63.52; H, 8.41; N, 8.55. Found: C,
63.38; H, 8.61; N, 8.34.
2(S)-[(ter t-Bu t yloxyca r b on yl)a m in o]-4-[N-[2-p h en yl-
1(R)-(ter t-bu tyloxyca r bon yl)eth yl]-N-a cetyla m in o]-N,N-
d im eth ylbu tyr a m id e (4RS-F ). The N-acetylation of 3RS-F
was carried out in the same manner as that of 4SS-F . The
product was obtained as a yellow oil: 84% yield; k′ ) 6.6 (30-
75% (v/v) A in B in 30 min); FAB-MS calcd for C26H41N3O6:
491.629, found: m/z ) 492 (M + H)+. Anal. Calcd for
C26H41N3O6: C, 63.52; H, 8.41; N, 8.55. Found: C, 63.32; H,
8.62; N, 8.35.
2(S)-[(ter t-Bu t yloxyca r b on yl)a m in o]-4-[N-[1(S)-(ter t-
bu tyloxyca r bon yl)eth yl]-N-a cetyla m in o]-N,N-d im eth yl-
bu tyr a m id e (4SS-A). The N-acetylation of 3SS-A followed
the procedure detailed above for 4SS-F . The product was
obtained as a yellow oil: 83% yield; k′ ) 7.6 (15-55%(v/v) A
in B in 30 min); FAB-MS calcd for C20H37N3O6: 415.531,
found: m/z ) 416 (M + H)+. Anal. Calcd for C20H37N3O6: C,
57.81; H, 8.98; N, 10.11. Found: C, 57.59; H, 9.17; N, 9.73.
2(S)-[(ter t-Bu t yloxyca r b on yl)a m in o]-4-[N-[1(R)-(ter t-
bu tyloxyca r bon yl)eth yl]-N-a cetyla m in o]-N,N-d im eth yl-
bu tyr a m id e (4RS-A). The N-acetylation of 3RS-A followed
the procedure detailed above for 4SS-F . The product was
obtained as a yellow oil: 80% yield; k′ ) 7.6 (15-55%(v/v) A
in B in 30 min); FAB-MS calcd for C20H37N3O6: 415.531,
found: m/z ) 416 (M + H)+. Anal. Calcd for C20H37N3O6: C,
57.81; H, 8.98; N, 10.11. Found: C, 57.89; H, 8.76; N, 10.10.
H exa h yd r o-1H -3-oxo-1-a cet yl-2(S)-b en zyl-5(S)-(N,N-
d im eth ylca r ba m oyl)-1,4-d ia zep in e (5SS-F ). An ice-cooled
solution of 4SS-F (0.15 g, 0.31 mmol) in DCM (2 mL) was
treated with trifluoroacetic acid (TFA) (2 mL) for 30 min
followed by 4 h at rt. The oily residue obtained after removal
of solvent and TFA under vacuo was dried over KOH pellets
overnight and yielded 2(S)-amino-4-[N-[2-phenyl-1(S)-carboxy-
ethyl]-N-acetylamino]-N,N-dimethylbutyramide trifluorocae-
tate as a white powder: k′ ) 3.0 (15-55%(v/v) A in B in 30
min); FAB-MS calcd for C17H25N3O4: 335.404, found: m/z )
336 (M + H)+. This trifluoroacetate salt was used in the next
step without further purification.
2(S)-[(ter t-Bu tyloxyca r bon yl)a m in o]-4-[[2-p h en yl-1(R)-
(ter t-b u t yloxyca r b on yl)et h yl]a m in o]-N,N-d im et h ylb u -
tyr a m id e (3RS-F ). Preparation of this diastereomer followed
the procedure described for (3SS-F ) except for employing tert-
butyl D-phenylalaninate hydrochloride. The pure product was
obtained as a clear oil (50% yield): Rf ) 0.35 (acetone-
petroleum ether/1:3); k′ ) 5.3 (30-75%(v/v) A in B in 30 min);
[R]25D ) -7.2 (c ) 0.815, methanol); 1H NMR (300 MHz, CDCl3)
δ 7.28-7.18 (5H, m, Ar), 5.54 (1H, d, J ) 9.0 Hz, NH
carbamate), 4.68 (1H, ddd, J ) 9.0, 4.2, 9.6 Hz, CH2CH2CH),
3.41 (1H, t, J ) 6.9 Hz, CHCH2Ph), 3.03 (3H, s, CH3N), 2.93
(3H, s, CH3N), 2.88 (2H, m, CHCH2Ph), 2.70 (1H, m, CH2CH2-
CH), 2.57 (1H, m, CH2CH2CH), 1.68 (2H, m, CH2CH2CH), 1.42
(9H, s, CH3 t-Bu), 1.32 (9H, s, CH3 t-Bu). 13C NMR (400 MHz,
CDCl3) δ 174.56 (CO), 172.9 (CO), 156.3 (CO), 138.1 (C-Ar),
138.1 (CH-Ar), 128.9 (CH-Ar), 127.2 (CH-Ar), 81.7 (C-t-Bu),
80.1 (C-t-Bu), 64.0 (CHCH2Ph), 49.2 (CH2CH2CH), 44.6 (CH2-
CH2CH), 40.5 (CHCH2Ph), 37.7 (CH3N), 36.4 (CH3N), 34.6
(CH2CH2CH), 29.0 (CH3 t-Bu), 28.7 (CH3 t-Bu); FAB-MS calcd
for C24H39N3O5: 449.592, found: m/z ) 450 (M + H)+. Anal.
Calcd for C24H39N3O5: C, 64.12; H, 8.74; N, 9.35. Found: C,
64.38; H, 8.77; N, 9.63.
2(S)-[(ter t-Bu tyloxyca r bon yl)a m in o]-4-[[1(S)-(ter t-bu -
t y lo x y c a r b o n y l)e t h y l]a m i n o ]-N ,N -d i m e t h y lb u t y r -
a m id e (3SS-A). Preparation followed the procedure described
for 3SS-F except for employing tert-butyl L-alaninate hydro-
chloride. Gravity chromatography on a silica gel 60 column
using step gradient of 66-80% acetone in petroleum ether as
eluent afforded a clear oil (47% yield): Rf ) 0.55 (acetone-
petroleum ether/4:1); k′ ) 6.1 (15-55% (v/v) A in B in 30 min);
[R]25 ) -23.4 (c ) 0.937, methanol); 1H NMR (300 MHz,
D
CDCl3) δ 5.49 (1H, d, J ) 8.4 Hz, NH carbamate), 4.70 (1H,
ddd, J ) 8.4, 4.8, 8.4 Hz, CH2CH2CH), 3.12 (1H, q, J ) 6.9
Hz, CHCH3), 3.06 (3H, s, CH3N), 2.91 (3H, s, CH3N), 2.71 (1H,
m, CH2CH2CH), 2.41 (1H, m, CH2CH2CH), 1.76 (1H, m,
CH2CH2CH), 1.62 (1H, m, CH2CH2CH), 1.41 (9H, s, CH3 t-Bu),
1.38 (9H, s, CH3 t-Bu), 1.18 (3H, d, J ) 6.9 Hz, CHCH3). 13C
NMR (300 MHz, CDCl3) δ 175.6 (CO), 172.9 (CO), 156.2 (CO),
81.5 (C), 80.1 (C), 57.9 (CHCH3), 49.1 (CH2CH2CH), 44.3 (CH2-
CH2CH), 37.6 (CH3N), 36.3 (CH3N), 34.5 (CH2CH2CH), 29.0
(CH3 t-Bu), 28.7 (CH3 t-Bu), 19.7 (CHCH3); FAB-MS calcd for
C18H35N3O5: 373.494, found: m/z ) 374 (M + H)+. Anal.
Calcd for C18H35N3O5: C, 57.89; H, 9.45; N, 11.25. Found: C,
57.79; H, 9.66; N, 11.45.
To an ice-cold solution of the trifluroacetate salt in dry DMF
(200 mL) were added NaHCO3 (130 mg, 1.55 mmol) and
diphenyl phosphorazidate (DPPA) (0.1 mL, 0.47 mmol). The
reaction mixture was stirred at 4 °C overnight under nitrogen
and monitored by analytical RP-HPLC. The ionic components
were removed by batch treatment for 3 h at 4 °C with 1.5 g of
Biorad AG 501-X8, mixed-bed ion-exchange resin. The resin
was removed by filtration and washed three-times with DMF.
The solvent from the combined filtrate and washes was
removed in vacuo. The residue obtained was purified by
semipreparative RP-HPLC (0-15% (v/v) A in B in 60 min on
a µBondapak column), affording 78 mg of white powder (79%
yield): k′ ) 3.6 (15-55%(v/v) A in B in 30 min); mp 129 °C;
2(S)-[(ter t-Bu tyloxyca r bon yl)a m in o]-4-[[1(R)-(ter t-bu -
t yloxyca r b on yl)e t h yl]a m in o]-N ,N -d im e t h ylb u t yr a m -
id e (3RS-A). This compound was prepared following the
procedure described for 3SS-F except for employing tert-butyl
D-alaninate hydrochloride. Gravity chromatography was per-
formed on a silica gel 60 column using step gradient of 66-
80% (v/v) acetone in petroleum ether as eluent afforded a clear
oil (43% yield): Rf ) 0.55 (acetone- petroleum ether/4:1); k′
) 6.1 (15-55%(v/v) A in B); [R]25 ) +10.7 (c ) 0.475,
D
1
methanol); H NMR (400 MHz, CDCl3) δ 5.56 (1H, d, J ) 8.4
Hz, NH carbamate), 4.71 (1H, ddd, J ) 8.4, 4.4, 8.4 Hz, CH2-
CH2CH), 3.20 (1H, q, J ) 6.8 Hz, CHCH3), 3.08 (3H, s, CH3N),
2.94 (3H, s, CH3N), 2.69-2.55 (2H, m, CH2CH2CH), 1.81 (1H,
m, CH2CH2CH), 1.64 (1H, m, CH2CH2CH), 1.45 (9H, s, CH3
t-Bu), 1.41 (9H, s, CH3 t-Bu), 1.23 (3H, d, J ) 6.8 Hz, CHCH3).
13C NMR (300 MHz, CDCl3) δ 175.8 (CO), 173.0 (CO), 156.3
(CO), 81.5 (C), 80.1 (C), 58.2 (CHCH3), 49.3 (CH2CH2CH), 44.5
(CH2CH2CH), 37.7 (CH3N), 36.4 (CH3N), 34.7 (CH2CH2CH),
29.1 (CH3 t-Bu), 28.8 (CH3 t-Bu), 19.8 (CHCH3); FAB-MS calcd
for C18H35N3O5: 373.494, found: m/z ) 374 (M + H)+. Anal.
Calcd for C18H35N3O5: C, 57.89; H, 9.45; N, 11.25. Found: C,
57.69; H, 9.67; N, 11.02.
[R]25 ) +65.5 (c ) 0.832, methanol); 1H NMR (500 MHz,
D
CDCl3) δ cis isomer (86%) 7.17-7.25 (5H, Ar), 6.63 (1H, NH),
4.79 (1H, CHCH2Ph), 4.43 (1H, CHCH2CH2), 4.40 and 3.04
(2H, CH2CH2CH), 3.46 and 3.12 (2H, CH2Ph), 3.00 and 2.94
(6H, N(CH3)2), 2.24 and 2.08 (2H, CH2CH2CH), 1.65 (3H, CH3-
CO); trans isomer (14%) 7.17-7.25 (5H, Ar), 6.79 (1H, NH),
and 5.55 (1H, CHCH2Ph).13C NMR (500 MHz, CDCl3) δ cis
isomer (86%) 174.6 (COCH3), 171.6 (CONH), 170.4 (CON-
(CH3)2), 129.0-136.7 (C- Ar), 65.4 (CHCH2Ph), 52.4 (CHNH),
38.6 (NCH2), 36.4 and 36.8 (N(CH3)2), 35.6 (CH2Ph), 30
(CH2CH2CH), 20.6 (CH3CO); trans isomer (14%) 36.4 and 36.8
(N(CH3)2). Detailed NMR assignment and conformational
analysis are published elsewhere.43 FAB-MS calcd for
2(S)-[(ter t-Bu t yloxyca r b on yl)a m in o]-4-[N-[2-p h en yl-
1(S)-(ter t-bu tyloxyca r bon yl)eth yl]-N-a cetyla m in o]-N,N-
d im eth ylbu tyr a m id e (4SS-F ). A solution of 3SS-F (140 mg,

3-Oxo-1H-1,4-diazepine-Based Peptidomimetic
J . Org. Chem., Vol. 62, No. 8, 1997 2533
C17H23N3O3: 317.389, found: m/z ) 318 (M + H)+. Anal.
Calcd for C17H23N3O3‚7/4H2O: C, 58.52; H, 7.66; N, 12.04.
Found: C, 58.53; H, 7.31; N, 11.57.
2.15 and 1.80 (CH2CH2CH), 2.16 (3H, CH3CO),1.37 (3H, CH3-
CH). 13C NMR (500 MHz, CDCl3) δ cis isomer (62%) 170.3
(CH3CO), 170 (CONH), 169.2 (CON(CH3)2), 58 (CHCH3), 49
(CHCH2CH2), 38.3 (CH2CH2CH), 35.8 and 36.5 (N(CH3)2), 28.7
(CH2CH2CH), 20.57 (CH3CO), 16.7 (CH3CH); trans isomer
(38%) 169.2 (CH3CO), 171 (CONH), 169 (CON(CH3)2), 55
(CHCH3), 48 (CHCH2CH2), 41.1 (CH2CH2CH), 35.8 and 36.5
(N(CH3)2), 30.7 (CH2CH2CH), 20.57 (CH3CO), 15.3 (CH3CH).
Detailed NMR assignment and conformational analysis are
published elsewhere.43 FAB-MS calcd for C11H19N3O3: 241.291,
found: m/z ) 242 (M + H)+.
ter t-Bu tyl 2(S)-[(Ben zyloxycar bon yl)am in o]-4-h ydr oxy-
bu tyr a te (7). A solution of Z-L-Asp-OtBu (6) (8.08 g, 25 mmol)
in dry THF (25 mL) and TEA (3.5 mL, 25 mmol) was cooled in
an ice-salt bath and treated with of isobutyl chloroformate
(IBCF) (3.3 mL, 25 mmol). After 30 min the triethylammo-
nium chloride precipitate was filtered off, and the filtrate was
added dropwise to a solution of NaBH4 (1.89 g, 50 mmol) in
water (10 mL) at 10 °C. After stirring at rt overnight, the
reaction mixture was slowly acidified (pH ≈ 3) with 1 N HCl
and extracted with EtOAc (4 × 100 mL). The combined
organic phases were washed consecutively with 1 N NaOH (4
× 150 mL) and brine (2 × 150 mL), dried over MgSO4, and
concentrated in vacuo. Gravity chromatography on silica gel
60 column using step-gradient of 10-50% (v/v) EtOAc in
petroleum ether afforded 5.18 g of a clear oil (67% yield): Rf
) 0.51 (33% (v/v) acetone in petroleum ether); k′ ) 3.2 (35-
95% (v/v) A in B); [R]25D ) -14.0 (c ) 0.75, AcOEt);52 1H NMR
(300 MHz, CDCl3) δ 7.34 (5H, m), 5.61 (1H, d, J ) 7.5 Hz),
5.11 (2H, s), 4.40 (1H, m), 3.68 (2H, m), 3.06 (1H, dd, J ) 5.1,
7.8 Hz), 2.15 (1H, m), 1.58 (1H, m), 1.45 (9H, s). FAB-MS calcd
for C16H23N1O5: 309.362, found: m/z ) 332 (M + Na)+. Anal.
Calcd for C16H23N1O5·0.5H2O: C, 60.36; H, 7.60; N, 4.40.
Found: C, 60.87; H, 7.48; N, 4.66.
H exa h yd r o-1H -3-oxo-1-a cet yl-2(R)-b en zyl-5(S)-(N,N-
d im eth ylca r ba m oyl)-1,4-d ia zep in e (5RS-F ). Deprotection
of 4RS-F followed the procedure described above for 5SS-F
and afforded 2(S)-amino-4-[N-[2-phenyl-1(R)-carboxyethyl]-N-
acetylamino]-N,N-dimethylbutyramide trifluoroacetate: k′ )
3.0 (15-25% A in B); FAB-MS calcd for C17H25N3O4: 335.404,
found: m/z 336 (M + H)+. Cyclization of the TFA salt in a
similar manner as detailed for 5SS-F and semipreparative RP-
HPLC purification ((0-15% A in B, 60 min, µBondapak)
afforded a white powder (82% yield): k′ ) 4.1 (15-55% A in
B); mp 192 °C; [R]25 ) -53.8 (c ) 0.550, methanol); 1H NMR
D
(500 MHz, CDCl3) δ cis isomer (73%) 7.14-7.24 (5H, Ar), 7.12
(1H, NH), 4.61 (1H, CHCH2Ph), 4.24 (1H, CHCH2CH2), 4.21
and 2.99 (2H, CH2CH2CH), 3.67 and 2.97 (2H, CH2Ph), 2.98
(6H, N(CH3)2), 2.55 and 1.70 (2H, CH2CH2CH), 1.49 (3H, CH3-
CO); trans isomer (27%) 7.14-7.24 (5H, Ar), 6.85 (1H, NH),
and 5.46 (1H, CHCH2Ph), 4.42 (1H, CHCH2CH2), 3.43 and 2.71
(2H, CH2CH2CH), 3.42 and 3.23 (2H, CH2Ph), 2.93 (6H,
N(CH3)2), 2.14 (3H, CH3CO), 2.03 and 1.63 (2H, CH2CH2CH).
13C NMR (500 MHz, CDCl3) δ cis isomer (73%) 168.8 (COCH3),
168.8 (CONH), 168.7 (CON(CH3)2), 129.4-136.7 (C Ar), 64.6
(CHCH2Ph), 48.6 (CHNH), 38.8 (NCH2), 35.8 (N(CH3)2), 36.4
(CH2Ph), 28.3 (CH2CH2CH), 19.5 (CH3CO); trans isomer (27%)
168.6 (CON(CH3)2), 168.4 (CONH), 137.1-130.0 (C Ar), 60.2
(CHCH2Ph), 48 (CHNH), 42.8 (NCH2), 35.8 (N(CH3)2), 34.4
(CH2Ph), 30.2 (CH2CH2CH), 20.8 (CH3CO). Detailed NMR
assignment and conformational analysis are published else-
where.43 FAB-MS Calcd for C17H23N3O3: 317.389 Found: m/z
) 318 (M + H)+. Anal. Calcd for C17H23N3O3·H2O: C, 60.88;
H, 7.51; N,12.53. Found: C, 60.77; H, 7.37; N, 12.16.
H exa h yd r o-1H -3-oxo-1-a cet yl-2(S)-m et h yl-5(S)-(N,N-
d im eth ylca r ba m oyl)-1,4-d ia zep in e (5SS-A). Deprotection
of 4SS-A followed procedure described above for 5SS-F and
afforded 2(S)-amino-4-[N-[1(S)-carboxyethyl]-N-acetylamino]-
N,N-dimethylbutyramide trifluoroacetate: k′ ) 3.6 (0-30% (v/
v) A in B); FAB-MS calcd for C11H21N3O4: 259.309, found: m/z
) 260 (M + H)+. Cyclization of the TFA salt in a similar
manner as described for 5SS-F above and purification on a
semipreparative RP-HPLC (0-25% (v/v) A in B, 100 min,
Vydac C-18) afforded an oil (62% yield): k′ ) 4.3 (0-30% (v/v)
ter t-Bu tyl 2(S)-[(Ben zyloxycar bon yl)am in o]-4-[[2-ph en -
yl-1(S)-(ben zyloxyca r bon yl)eth yl]a m in o]bu tyr a te (8). A
solution of alcohol 7 (4.94 g, 16 mmol) in dry DCM (40 mL)
was added to a suspension of PCC (13.8 g, 64 mmol) and silica
gel 60 (13.8 g) in dry DCM (40 mL). The reaction was
monitored by TLC Rf ) 0.60 (33% (v/v) acetone in petroleum
ether) and analyzed by ninhydrin. After 2.5 h, diethyl ether
(100 mL) was added, and the mixture was filtered through
Celite bed. The crude aldehyde obtained upon removal of
solvent from the filtrate in vacuo was dissolved in 2% (v/v)
AcOH in MeOH (20 mL) and mixed with a solution of L-H-
Phe-OBz tosylate (3.55 g, 8.3 mmol) in methanol (22 mL) in
the presence of molecular sieves Type 3Α (8-12 mesh) pellets
(∼5 g). After 5 min, NaCNBH3 (1.15 g, 18.3 mmol) was added
in two aliquots. After 1.5 h, the reaction mixture was filtered
and the solvent removed in vacuo. The residue was treated
with saturated NaHCO3 (250 mL) and extracted with diethyl
ether (3 × 400 mL). The combined ethereal phases were dried
over MgSO4 and concentrated in vacuo. Purification on silica
gel 60 column employing a step-gradient of 20-25% (v/v)
acetone/petroleum ether as eluent afforded 3.05 g of a clear
oil (67% yield, based on the benzyl phenylalaninate salt): Rf
) 0.45 (25% (v/v) acetone in petroleum ether); k′ ) 6.3 (35-
A in B); [R]25 ) +109.1° (c ) 0.430, methanol); 1H NMR (500
D
MHz, CDCl3) δ cis isomer (88%) 6.55 (1H, NH), 4.7 (1H,
CHCH3), 4.4 (1H, CHNH), 4.52 and 3.02 (2H, NCH2CH2), 2.99
and 2.95 (6H, N(CH3)2), 1.98 (CH2CH2CH), 2.13 (3H, CH3CO),
1.56 (3H, CH3CH); trans isomer (12%) 6.55 (1H, NH), 5.2 (1H,
CHCH3), 4.5 (1H, CHNH), 3.77 and 3.58 (2H, NCH2CH2), 2.95
(6H, N(CH3)2), 1.98 (CH2CH2CH), 1.51 (3H, CH3CH). 13C NMR
(500 MHz, CDCl3) δ cis isomer (88%) 170.9 (CH3CO), 174
(CONH), 170.1 (CON(CH3)2), 59 (CHCH3), 52 (CHCH2CH2),
38.5 (CH2CH2CH), 37.1 (N(CH3)2), 31.25 (CH2CH2CH), 21.93
(CH3CO), 15.47 (CH3CH); trans isomer (12%), 174 (CONH),
174.4 (CON(CH3)2), 56 (CHCH3), 51 (CHCH2CH2), 43.3 (CH2-
CH2CH), 36.4 (N(CH3)2), 32.7 (CH2CH2CH). Detailed NMR
assignment and conformational analysis are published else-
where.43 FAB-MS calcd for C11H19N3O3: 241.291, found: m/z
) 242 (M + H)+.
95% (v/v) A in B); [R]25 ) -6.8° (c ) 0.558, methanol); 1H
D
NMR (300 MHz, CDCl3) δ 7.33-7.07 (15H, m, Ar), 5.93 (1H,
d, J ) 7.8 Hz, NH carbamate), 5.10 (2H, s, CH2Ph), 5.05 (2H,
s, CH2Ph), 4.26 (1H, dd, J ) 7.8, 12.0 Hz, CH2CH2CH), 3.52
(1H, t, J ) 6.9 Hz, CHCH2Ph), 2.92 (2H, m, CHCH2Ph), 2.74
(1H, m, CH2CH2CH), 2.50 (1H, m, CH2CH2CH), 1.90 (1H, m,
CH2CH2CH), 1.77 (1H, m, CH2CH2CH), 1.43 (9H, s, CH3 tBu).
13C NMR (400 MHz, CDCl3) δ 174.1 (CO), 171.3 (CO), 156.0
(CO), 136.8 (C-Ar), 136.5 (C-Ar), 135.4 (C-Ar), 129.2 (CH-Ar),
128.5 (CH-Ar), 128.5 (CH-Ar), 128.4 (CH-Ar), 128.4 (CH-Ar),
128.3 (CH-Ar), 128.1 (CH-Ar), 128.0 (CH-Ar), 126.7 (CH-Ar),
81.9 (C-t-Bu), 66.8 (CH2Ph), 66.5 (CH2Ph), 62.7 (CHCH2Ph),
53.3 (CH2CH2CH), 44.2 (CH2CH2CH), 39.7 (CHCH2Ph), 31.9
(CH2CH2CH), 28.0 (CH3 t-Bu). FAB-MS calcd for
C32H38N2O6: 546.664, found: m/z ) 547 (M + H)+. Anal.
H exa h yd r o-1H -3-oxo-1-a cet yl-2(R)-m et h yl-5(S)-(N,N-
d im eth ylca r ba m oyl)-1,4-d ia zep in e (5RS-A). Deprotection
of 4RS-A followed the procedure described above for 5SS-F
and afforded (2(S)-amino-4-[N-[1(R)-carboxyethyl]-N-acetyl-
amino]-N,N-dimethylbutyramide trifluoroacetate: k′ ) 3.7 (0-
30% (v/v) A in B); FAB-MS calcd for C11H21N3O4: 259.309,
found: m/z ) 260 (M + H)+. Cyclization of the TFA salt in a
similar manner as described for 5SS-F above and purification
similar to that described for 5SS-A afforded an oil (88%
yield): k′ ) 4.7 (0-30% (v/v) A in B); [R]25 ) -103.2° (c )
D
0.250, methanol); 1H NMR (500 MHz, CDCl3) δ cis isomer
(62%) 6.98 (1H, NH), 4.6 (1H, CHCH3), 4.3 (1H, CHNH), 4.22
and 2.95 (2H, NCH2CH2), 2.96 and 2.95 (6H, N(CH3)2), 2.47
and 1.65 (CH2CH2CH), 2.18 (3H, CH3CO),1.51 (3H, CH3CH);
trans isomer (38%) 6.79 (1H, NH), 5.2 (1H, CHCH3), 4.4 (1H,
CHNH), 3.80 and 3.35 (2H, NCH2CH2), 2.99 (6H, N(CH3)2),
(52) Valerio, R. M.; Alewood, P. E.; Hohns, R. B. Synthesis 1988,
786.

2534 J . Org. Chem., Vol. 62, No. 8, 1997
Weitz et al.
Calcd for C32H38N2O6: C, 70.31; H, 7.01; N, 5.12. Found: C,
70.23; H, 6.90; N, 5.20.
(100 mL), washed with saturated solution of NaHCO3 (3 ×
100 mL) and brine (30 mL), and dried over MgSO4 and the
solvent removed in vacuo. Purification by semipreparative RP-
HPLC on Vydac C-18, 300 Å (0-10% (v/v) in 20 min followed
by 10-40% in 90 min) afforded 49 mg of white powder (40%
ter t-Bu tyl 2(S)-a m in o-4-[[2-p h en yl-1(S)-ca r boxyeth yl]-
a m in o]bu tyr a te Tr iflu or oa ceta te (9). A nitrogen-flushed
solution of 8 (1.42 g, 2.6 mmol) in MeOH (12 mL)/AcOH (2
mL)/H2O (1 mL) was treated with 10% Pd/C (0.56 g) and
ammonium formate (0.66 g, 10.4 mmol). The reaction was
monitored by HPLC. Upon completion, the reaction mixture
yield): k′ ) 9.0 (5-50% (v/v) A in B); mp 73 °C; [R]25 ) +7.6
D
(c ) 0.275, methanol); 1H NMR (400 MHz, CDCl3) δ 7.30-
7.22 (5H, m, Ar), 6.80 (1H, d J ) 5.2 Hz, NHCO), 4.30 (1H,
ddd J ) 4.8, 4.8, 9.6 Hz, CH2CH2CH), 4.21 (1H, t J ) 6.8 Hz,
CHCH2Ph), 3.40-3.18 (3H overlapping CHCH2Ph CH2CH2-
CH), 3.03 (1H, m, CH2CH2CH), 2.38 (1H, m, CH2CH2CH), 2.08
(1H, m, CH2CH2CH),1.48 (9H, s, (CH3)3C). 13C NMR (300
MHz, CDCl3) δ 169.4 (CO), 169.2 (CO), 135.2 (C-Ar), 130.0
(CH-Ar), 129.6 (CH-Ar), 128.3 (CH-Ar), 85.0 (C t-Bu), 63.7
(CH2CH2CH), 51.9 (CHCH2Ph), 43.7 (CH2CH2CH), 36.6 (CH2-
Ph), 30.1 (CH2CH2CH), 20.5 (CH3 t-Bu). FAB-MS calcd for
was filtered through
a Celite bed, and the filtrate was
concentrated in vacuo. The residue obtained was lyophilized
three times from TFA/H2O to afford a white powder (1.39 g)
1
of the TFA salt (97% yield): k′ ) 5.1 (5-50% (v/v) A in B); H
NMR (400 MHz, D2O) δ 7.46-7.33 (5H, m, Ar), 4.25(1H, t J )
6.4 Hz, CHCH2Ph), 4.04 (1H, dd J ) 4.8, 7.6 Hz, CHCH2CH2),
3.40-3.27 (4H, m, CHCH2CH2, CHCH2Ph), 2,29 (2H, m,
CHCH2CH2), 1.26 (9H, s, CH3 t-Bu; FAB-MS calcd for
C17H26N2O4: 322.405, found: m/z ) 323 (M + H)+.
C
17H24N2O3: 304.39, found: m/z ) 305 (M + H)+. Anal. Calcd
H exa h yd r o-1H -3-oxo-2(S)-b en zyl-5(S)-ter t-b u t yloxy-
ca r bon yl)-1,4-d ia zep in e Tr iflu or oa ceta te (10). A solution
of the TFA salt 9 (0.16 g. 0.29 mmol) in DMF (150 mL) was
treated with DIPEA (0.1 mL, 0.58 mmol) and O-7-aza-1-
hydroxybenzotriazolyl-N,N,N′,N′-tetramethyluronium hexaflu-
orophosphate (HATU) (0.22 g, 0.58 mmol). The mixture was
stirred at rt under nitrogen overnight (complete disappearance
of the characteristic yellow color and the starting material as
monitored by analytical RP-HPLC). The residue obtained
following concentration in vacuo was dissolved with EtOAc
for C17H24N2O3·3/2TFA: C, 50.53; H, 5.41; N, 5.89. Found: C,
50.86; H, 5.64; N, 6.36.
This research was supported, in part, by grant No. 89-00248
from the United States-Israel Binational Science Foundation
(BSF), J erusalem, Israel (M.C.). D.F.M. would like to thank
the Research Corporation for partial support of this research
in the form of a Cottrell Scholar Award.
J O962257E