C-Alkylation of Peptides Containing Aminomalonate and (Amino)(cyano)acetate Residues

Article abstract of DOI:10.1002/(SICI)1522-2675(19981007)81:10<1845::AID-HLCA1845>3.0.CO;2-L

N-Acetyl-, N-[(tert-butoxy)carbonyl](Boc)-, and N-[(benzyloxy)carbonyl](Z)-protected tri-, penta-, and heptapeptide methyl esters, 1-8, with a central aminomalonate (Ama) (allyl, methyl, benzyl, or tert-butyl) or (amino)(cyano)acetate (Aca) residue have been prepared by conventional techniques (Schemes 4-6). The new peptides with acidic backbone-bound CH groups can be C-alkylated with primary alkyl, allyl, and benzyl halides, under mildly basic conditions (1 equiv. MeONa or t-BuOK in THF); also, they can be added to Michael acceptors such as acrylates, acrylonitrile, methyl vinyl ketone, or nitrostyrene (catalytic amounts of alkoxide bases in THF) (Schemes 7-16). In most cases, the products, 48-100, are formed in excellent yields (average of 77%); one of the epimeric products prevails (2:1 to > 20:1), and the epimers have been separated, isolated in pure form, and fully characterized (without configurational assignments); addition of the co-solvent 3,4,5,6-tetrahydro-1,3-dimethylpyrimidin-2(1H)-one (DMPU) or of LiBr may improve or even reverse the ratio of epimeric products formed; the heptapeptide derivative 8 had to be solubilized for alkylations in THF by the addition of 30 equiv. of LiBr. Cleavage of the Ama groups (benzyl with H₂/Pd-C, t-Bu with HCl/Et₂O) gave carboxylate derivatives which are actually peptides containing the alkylated aminomalonic acid, the lower homolog of aspartic acid, as residue in the central position. These acids are quite resistant to decarboxylation which had to be achieved by heating at reflux in THF in the presence of 2 equiv. of LiBr and of catalytic amounts of pyridine (Schemes 17 and 18). A one-step removal of the allyl aminomalonate group is possible with Pd/PPh₃/formate (Scheme 19). The resulting peptides, 101-115, were formed as separable 1:1 mixtures of two epimers. The CN group of the alkylated Aca residue can be removed reductively (Na/NH₃; Scheme 20). The value of the new method is compared with that of existing methods of peptide-backbone modification.

Full text of DOI:10.1002/(SICI)1522-2675(19981007)81:10<1845::AID-HLCA1845>3.0.CO;2-L

Helvetica Chimica Acta ± Vol. 81 (1998)
1845
1
C-Alkylation of Peptides Containing Aminomalonate ) and
(
Amino)(cyano)acetate Residues
2
by Thomas Matt ) and Dieter Seebach*
Laboratorium für Organische Chemie der Eidgenössischen Technischen Hochschule, ETH-Zentrum,
Universitätstrasse 16, CH-8092 Zürich
Dedicated to Professor Heinrich Nöth on the occasion of his 70th birthday
N-Acetyl-, N-[(tert-butoxy)carbonyl](Boc)-, and N-[(benzyloxy)carbonyl](Z)-protected tri-, penta-, and
heptapeptide methyl esters, 1 ± 8, with a central aminomalonate (Ama) (allyl, methyl, benzyl, or tert-butyl) or
(amino)(cyano)acetate (Aca) residue have been prepared by conventional techniques (Schemes 4 ± 6). The new
peptides with acidic backbone-bound CH groups can be C-alkylated with primary alkyl, allyl, and benzyl
halides, under mildly basic conditions (1 equiv. MeONa or t-BuOK in THF); also, they can be added to Michael
acceptors such as acrylates, acrylonitrile, methyl vinyl ketone, or nitrostyrene (catalytic amounts of alkoxide
bases in THF) (Schemes 7 ± 16). In most cases, the products, 48 ± 100, are formed in excellent yields (average of
77%); one of the epimeric products prevails (2 :1 to > 20 : 1), and the epimers have been separated, isolated in
pure form, and fully characterized (without configurational assignments); addition of the co-solvent 3,4,5,6-
tetrahydro-1,3-dimethylpyrimidin-2(1H)-one (DMPU) or of LiBr may improve or even reverse the ratio of
epimeric products formed; the heptapeptide derivative 8 had to be solubilized for alkylations in THF by the
2 2
addition of 30 equiv. of LiBr. Cleavage of the Ama groups (benzyl with H /Pd-C, t-Bu with HCl/Et O) gave
carboxylate derivatives which are actually peptides containing the alkylated aminomalonic acid, the lower
homolog of aspartic acid, as residue in the central position. These acids are quite resistant to decarboxylation
which had to be achieved by heating at reflux in THF in the presence of 2 equiv. of LiBr and of catalytic
amounts of pyridine (Schemes 17 and 18). A one-step removal of the allyl aminomalonate group is possible with
Pd/PPh
epimers. The CN group of the alkylated Aca residue can be removed reductively (Na/NH
value of the new method is compared with that of existing methods of peptide-backbone modification.
3
/formate (Scheme 19). The resulting peptides, 101 ± 115, were formed as separable 1 : 1 mixtures of two
3
; Scheme 20). The
1. Introduction. ± Modified natural peptides and proteins are widely used for
investigations of structure-activity correlations. Usually, these oligopeptides are
prepared by stepwise procedures [2]. In contrast, methods based on the chemical
modification of intact peptides would be more attractive and more economical for the
preparation of a multitude of derivatives, without having to repeat the peptide synthesis
for each modification.
Over the past ten years, we have developed a methodology by which new side chains
can be attached via enolates of sarcosine or glycine residues within a peptide chain
[
3 ± 5]. Analogous modifications using nucleophilic reactivity have also been reported
by other groups [6]. The generation of electrophilic glycine equivalents within peptides
using electrochemical decarboxylation [7], oxidative cleavage of serine or threonine
residues [8], or bromination with N-bromosuccinimide [9] has also been realized.
1)
2)
For a preliminary communication, see [1].
Part of the Dissertation No. 12307 of T.M., ETH-Zürich, 1997.

1846
Helvetica Chimica Acta ± Vol. 81 (1998)
In previous papers [3 ± 5] about peptide enolates, we demonstrated that linear and
cyclic oligopeptides containing up to eleven amino acids can be alkylated at glycine or
sarcosine residues via polylithiated derivatives. The glycine- or sarcosine-enolate
reactive sites were generated by deprotonation of the least acidic position in the
peptide backbone using strong bases. However, this procedure was only applicable if an
N-alkylated amino acid was incorporated adjacent to the peptide-enolate unit in the
direction of the C-terminus. Also special precautions were necessary for providing
anhydrous and oxygen-free conditions. The purpose of this paper is to describe a
project for reversing this situation [9]: the position to be substituted is now the most
acidic one in the molecule (Scheme 1). This goal should be achieved by substitution of
one a-CH proton of a glycine residue by an electron-withdrawing group, e.g., a
carboxyalkyl (CO R') or a CN group.
2
Scheme 1
In other words, the incorporation of an aminomalonic acid monoester (Ama
3
monoester) ) or an aminocyanoacetic-acid (Aca) building block into a peptide should
render the adjacent backbone CH group the most acidic position within the molecule.
Weaker bases and, therefore, milder conditions could be used for nucleophile
generation. The modification of oligopeptides, that are not N-alkylated should be
then possible. The synthetic potential of this approach (i.e., application of the classical
malonic-ester synthesis to peptides) is indicated in Scheme 2.
3)
Ama-Containing peptides are not unknown in the literature: a diketopiperazine [10], a tripeptide [11], and
some peptide isosteres [12], containing at least one Ama building block, have been reported. Ama was also
detected in alkaline hydrosylates of proteins of E. coli; a content of 0.3 Ama/1000 amino acids was found.
The origin of the Ama residues is still unclear; it has been demonstrated that Ama is not formed from any
of the 20 proteinogenic amino acids during the hydrolysis procedure [13].

Helvetica Chimica Acta ± Vol. 81 (1998)
1847
Scheme 2
R
O
R
R
O
R
H
N
H
H
N
H
N
Base
N
N
H
N
H
N
H
N
H
O
O
O
O
O
OR'
LiO
OR'
A
B
Electrophile
R
O
R
R
O
R
H
N
H
H
N
H
N
–
COOR'
N
N
H
N
H
N
N
H
H
RE
O
RE
R'O
O
O
O
O
D
C
Deprotonation of A gives the new enolate derivative B (geometry (E/Z) of the
enolate double bond is unknown). The subsequent alkylation of B leads to the
corresponding a,a-disubstituted derivative C, which is finally converted to the modified
peptide D by cleavage of the electron-withdrawing group.
2
. Ama- and Aca-Containing Peptides, the Starting Materials. ± The peptides 1 ± 8
containing three to seven amino acids were prepared. The Ama or Aca building block
was always positioned in the middle of the peptides. The other amino-acid components
were chosen according to previous work [3]. Except in 1 and 8, the ester group of the
Ama side chain was designed to be cleaved selectively.
We prepared the Ama-monoester building blocks in a straightforward manner4)
(
Scheme 3). The N-protected glycine esters were doubly deprotonated by lithium
diisopropylamide (LDA)/N,N,N',N'-tetramethylethylenediamine (TMEDA) and car-
boxylated with CO gas, yielding the corresponding N-protected Ama monoesters
2
(
9 ± 12). Treatment of 10 with CH N gave the Ama-diester derivative 13, which is
2 2
required for the preparation of 8. Using the same deprotonation-carboxylation
procedure, Boc-protected amino-acetonitrile 14 could be converted to Boc-Aca-OH
(15). The building blocks 9 ± 12 and 15 were used without further purification.
Surprisingly, these building blocks could be activated and incorporated into peptides by
conventional methods, without any ꢀdecarboxylation problemsꢁ.
The assembly of the peptides 1 ± 8 is schematically presented in Schemes 4 ± 6
(
intermediates 16 ± 47). Except for 8, all peptides were built up from C to N terminus.
The N-protected amino acids (Z- or Boc-) were activated by isobutyl chlorocarbonate
in THF)/N-methylmorpholine (NMM); dicyclohexylcarbodiimide (DCC)/1-hy-
droxy-1H-benzotriazole (HOBt) or 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide
EDC)/HOBt was employed for the coupling of the N-protected Ama building blocks.
(
(
4)
Another method for the preparation of this half ester has been described by U. Schmidt et al. [14].

1848
Helvetica Chimica Acta ± Vol. 81 (1998)
R2
O
O
O
O
O
CN
O
H
N
H
H
H
N
N
N
R1
N
H
O
Boc
N
O
H
O
O
1
2
4
1
2
3
R = Boc, R = Me
1
2
R = Boc, R = Bn
1
R = Ac, R = t-Bu
2
O
O
O
O
H
H
H
N
N
N
R1
N
H
N
O
H
H
O
O
O
R2
1
2
5
6
7
R = Z, R = t-Bu
1
2
R = Boc, R = Bn
1
2
R = Boc, R = All
O
O
O
H
H
N
N
H
H
Boc
N
N
O
N
N
N
H
H
H
O
O
O
O
O
O
8
We exclusively used sat. HCl/Et O solution for removal of the Boc protecting group,
2
and Pd/C under H for cleavage of the Z group.
2
Finally, the heptapeptide 8 was assembled by a fragment-condensation technique
(
Scheme 6): the two peptide fragments, H-Val-Ala-Leu-OMe (40) and Boc-Val-Ala-
Leu-Ama(OMe)-OH (47), were first built up using the strategy described above. The
reaction of 40 and 47 was carried out in THF at 08 in the presence of EDC/HOBt as
activating reagents (! 8, 50%).
The peptide derivatives were obtained as mixtures of two epimers which could not
be separated, with one exception: a single epimer of the tert-butyl malonate 3

Helvetica Chimica Acta ± Vol. 81 (1998)
1849
Scheme 3
R2
O
O
O
1
) 2.2 equiv. LDA,
R1
O
R1
OH
2.2 equiv. TMEDA
N
R2
N
H
H
2) CO , THF, – 78˚
2
O
Product
R1
R2
Me
9
CO2CMe3 (Boc)
10
11
12
Boc
Bn
All
Boc
CO2Bn (Z)
t-Bu
Bn
Bn
O
O
O
O
CH2N2
78 %
Boc
OH
Boc
O
N
H
N
H
O
O
10
13
O
1
) 2.2 equiv. LDA,
H
H
HCl·H2N
CN
Boc2O
6 %
O
N
CN
2.2 equiv. TMEDA
O
N
OH
9
2) CO2, THF, – 78˚
O
O
CN
14
15
(
unknown configuration) separated from the workup solution. The peptide derivatives
, 5, and 8 were rather insoluble in organic solvents. For details of the oligopeptide
syntheses, see Exper. Part and standard procedures [15].
3
3
. Deprotonation and Alkylation of the Ama-Containing Peptides 1 ± 3, 5 ± 8, and
the Aca-Containing Tripeptide 4. ± The deprotonation and subsequent alkylation were
carried out first with the Boc-tripeptide diester 1. We chose NaOMe in MeOH as base,
which was employed in slight stoichiometric exces (1.3 equiv.) for alkylation and
substoichiometrically (0.3 equiv.) for Michael additions to acrylic-acid derivatives,
methyl vinyl ketone, and nitrostyrene. The reactions were usually carried out in THF at
0
8. As can be seen from Scheme 7, the tripeptide 1 reacted with a wide range of different
electrophiles. Using these conditions, the methylated product 48 was obtained in 84%
yield. All other alkyl halides also gave good results: EtI (! 49), BuI (! 50), allyl and
benzyl bromide (! 51 and 52, resp.), and cyclohex-2-enyl bromide (! 53). This
procedure could also be successfully used for Michael additions of the enolate of 1 to
methyl acrylate (! 54), to tert-butyl acrylate (! 55), acrylonitrile (! 56), and methyl

1850
Helvetica Chimica Acta ± Vol. 81 (1998)
Scheme 4

Helvetica Chimica Acta ± Vol. 81 (1998)
1851
Scheme 5
vinyl ketone (! 57). The reaction of 1 with nitrostyrene led to the formation of adduct
8. In all cases, the products were obtained as 1 : 1 mixture of two diastereoisomers; in
5
1
the case of 53 and 58, four isomers were detected by H-NMR analysis. All attempts to
separate the diastereoisomers were unsuccessful.

1852
Helvetica Chimica Acta ± Vol. 81 (1998)
Scheme 6
Scheme 7
Electrophile
Producta)
R
Yield [%]
MeI
EtI
BuI
48
49
50
51
52
Me
Et
Bu
CH
Bn
84
61
31
85
81
79
90
86
89
70
57
CH
2
ˆCHCH
2
Br
2
CHˆCH
2
BnBr
b
Cyclohex-2-enyl bromide
Methyl acrylate
tert-Butyl acrylate
Acryl nitrile
Methyl vinyl ketone
Nitrostyrene
53 )
cyclohex-2-en-1-yl
54
55
56
57
CH
CH
CH
CH
2
2
2
2
CH
CH
CH
CH
2
2
2
2
CO
CO
CN
2
Me
Bu
t
2
COMe
b
58 )
2 2
CH(Ph)CH NO
a) 1 : 1 Mixture of two diastereoisomers. b) Four isomers were detected by H-NMR.
1

Helvetica Chimica Acta ± Vol. 81 (1998)
1853
Applying the same procedure, the benzyl malonate 2 could be readily alkylated with
MeI (! 59), EtI (! 60), allyl bromide (! 61), and BnBr (! 62), or again, added in a
Michael fashion to methyl acrylate (! 63), to tert-butyl acrylate (! 64), to acrylonitrile
(
! 65), and to methyl vinyl ketone (! 66) (Scheme 8). We noticed a pronounced effect
5
of added LiBr on the diastereoselectivity of this alkylation ). The product ratio for the
methylation of 2 increased from 1 : 1 (no LiBr) to almost 6 : 1 (3 equiv. of LiBr). An
enhancement of the diastereoselectivity by adding 3 equiv. of LiBr was also observed
for the alkylation with allyl (2 : 1) and benzyl bromide (3 : 1). In contrast, for the
Michael addition of 2 no LiBr was required to obtain products which were enriched in
one epimer. The best result was obtained using tert-butyl acrylate as electrophile (dr
2
0 : 1). The configuration of the major products formed was not determined.
Scheme 8
Electrophile
LiBr [equiv.]
Product
R
Yield [%]
dra)
1 : 1
MeI
MeI
MeI
EtI
0
3
5
3
0
3
0
3
0
0
0
0
59
59
59
60
61
61
62
62
63
64
65
66
Me
Me
Me
Et
CH
CH
Bn
88
88
79
34
72
64
70
63
84
95
92
88
5.5 : 1
5 : 1
2 : 1
1 : 1
2 : 1
1 : 1
3 : 1
5 : 1
20 : 1
2 : 1
3 : 1
CH
CH
BnBr
BnBr
2
ˆCHCH
ˆCHCH
2
Br
Br
2
2
CHˆCH
CH� CH
2
2
2
2
Bn
Methyl acrylate
tert-Butyl acrylate
Acryl nitrile
CH
CH
CH
CH
2
2
2
2
CH
CH
CH
CH
2
2
2
2
CO
CO
CN
2
2
Me
Bu
t
Methyl vinyl ketone
COMe
a) The diastereoselectivity was determined by H-NMR spectroscopy.
1
Finally, the tert-butyl malonate 3 could be used for alkylations both as a single
isomer and as a 1 :1 mixture of two isomers (Scheme 9). In this case, LiBr was necessary
6
for better solubilization ). In the methylation of 3 (single isomer), we found again that
the selectivity could be increased by the addition of LiBr. The best result was obtained
by adding 3 equiv. of LiBr (! 67; 86%, dr 12 : 1). If 3 was used as a 1 : 1 mixture of
diastereoisomers, the methylated product 67 was obtained with reduced selectivity
(
2.5 : 1). This result indicates that the deprotonation of the two epimers probably leads
to different (E)/(Z)-enolate mixtures, and that each of these enolates might give one of
5)
6)
For a general discussion of this effect, see [3a].
Peptides can be solubilized in THF and other organic solvents by addition of salts, an effect which turned
out to be especially strong with Li salts [16].

1854
Helvetica Chimica Acta ± Vol. 81 (1998)
the two possible diastereoisomers preferentially. As can be seen from Scheme 9, using
malonate 3 as a single isomer and 3 equiv. of LiBr, the alkylation products, 68 ± 73, were
obtained in excellent yields, and some of them were highly enriched in one epimer. The
selectivities range from 2 : 1 for the ethylation (! 68) up to 12 : 1 for the reaction with
methyl acrylate (! 71). Without adding LiBr, the additon of the enolate of 3 to methyl
acrylate gave a preference for one isomer of only 4.5 : 1.
Scheme 9
Entrya)
Electrophile
LiBr [equiv.]
Product
R
Yield [%]
drb)
3 : 1
2.5 : 1
5 : 1
12 : 1
9 : 1
2 : 1
4 : 1
4 : 1
4.5 : 1
12 : 1
3 : 1
1
2
3
4
5
6
7
8
9
MeI
MeI
MeI
MeI
MeI
EtI
0
3
0
3
5
3
3
3
0
3
3
3
67
67
67
67
67
68
Me
Me
Me
Me
Me
Et
CH
Bn
CH
CH
CH
CH
89
88
89
86
90
35
48
66
91
90
88
91
c
CH
BnBr
2
ˆCHCH
2
69 )
70 )
2
CHˆCH
2
c
Methyl acrylate
Methyl acrylate
Acrylonitrile
71
71
72
73
2
CH
2
CH
2
CH
2
CH
2
2
2
2
CO
CO
CN
2
Me
Me
10
11
12
2
Methyl vinyl ketone
COMe
4 : 1
a) For Entry 1 and 2, 3 was used as a 1 : 1 mixture. For Entries 3 ± 12, the educt was used as a single isomer of
b
1
c
unknown configuration. ) The diastereoselectivity was determined by H-NMR spectroscopy. ) Separated
by FC.
Because of the excellent results obtained in the tripeptide malonate cases, we next
tested the alkylation of Ama-containing pentapeptide derivative 5. In this case, t-BuOK
5
was used as base, and it was necessary to add LiBr to achieve good solubilization ) in
THF. In the methylation of 5, the selectivity could be increased in the presence of
increasing amounts of LiBr (Scheme 10); but, compared to the tripeptide cases, the
enhancement was rather poor. The best result was achieved by adding 25 equiv. of LiBr
(
!74; 88%, dr 3 : 1). A stronger effect on the diastereoselectivity was observed by
7
adding 3,4,5,6-tetrahydro-1,3-dimethylpyrimidin-2(1H)-one (DMPU) ) as a co-sol-
vent instead of LiBr. Using a 5 : 1 mixture of THF/DMPU, the methylated product 74
was obtained as a 5 : 1 mixture of two isomers. With less DMPU, the selectivity
decreased (dr 3 : 1 with THF/DMPU 7.5 : 1). The methylation of 5 in other solvents
(
except in 1,2-dimethoxyethane (DME)) in combination with DMPU gave similar
selectivities (see Scheme 10).
7)
For reviews describing the co-solvent effect of DMPU, see the corresponding chapter in [3a].

Helvetica Chimica Acta ± Vol. 81 (1998)
1855
Scheme 10
Solvent
LiBr [equiv.]
Yield [%]
dra)
1 : 1.2
2.2 : 1
3 : 1
2 : 1
3 : 1
5 : 1
4.7: 1
4.7: 1
4.3 : 1
1 : 1
THF
THF
THF
THF
THF/DMPU )
THF/DMPU
2
10
25
30
0
0
0
0
0
0
77
82
91
92
85
92
86
84
93
90
b
5 : 1
5 : 1
5 : 1
5 : 1
5 : 1
5 : 1
Et
CH
2
O/DMPU
Cl /DMPU
2
2
Toluene/DMPU
c
DME )/DMPU
a) The diastereoselectivity was determined by HPLC (LiChrosorb; hexane/i-PrOH 96 : 4). b) DMPU: 3,4,5,6-
c
Tetrahydro-1,3-dimethylpyrimidin-2(1H)-one. ) DME: 1,2-Dimethoxyethane.
As can be seen from Scheme 11, under optimized conditions (THF/DMPU 5 :1;
t-BuOK; 08), a multitude of electrophiles reacted with the enolate derivative of 5
giving yields of up to 95% (74 ± 84). Even less activated electrophiles, e.g., EtI or BuI,
could be used successfully (! 75 and 76). The products are in some cases highly
enriched in one epimer. The best results were obtained for the reaction with tert-butyl
1
acrylate: only one isomer was detected in the crude product by H-NMR spectroscopy
(
(
! 82; 87%, dr >95 : 5)! The selectivities for the other reactions ranged from 2 : 1
addition to methyl vinyl ketone) to 9 : 1 (benzylation). In this case, all product
mixtures (except 80) could be separated by chromatographic methods. For isolation
and identification of these products, see Exper. Part. The configuration of the products
at the alkylated Ama residue was not determined.
The results obtained for the alkylations of the pentapeptide 6, with the Ama benzyl
ester incorporated, are shown in Scheme 12. Using the standard reaction condition
(t-BuOK; THF; 08), the alkylation products, 85 ± 90, were isolated in 60 ± 90% yield
and were highly enriched in one epimer. No Li salt for solubilization was necessary in
this case. The product 89 derived from the addition to tert-butyl acrylate was obtained
diastereoisomerically pure. Except in the case of 87 and 88, the diastereoisomeric
products could be chromatographically separated. For isolation and full identification
8
of these products, see Exper. Part. The major product of the benzylated derivative 86a )
gave crystals from MeOH suitable for X-ray analysis (Fig. 1). According to the crystal
structure, the new stereogenic center in 86a has (S)-configuration.
8)
We use a and b throughout this paper for specifying the two epimers of peptide alkylation products.

1856
Helvetica Chimica Acta ± Vol. 81 (1998)
Scheme 11
Electrophile
Producta)
R
Yield [%]
drb)
5 : 1
4 : 1
2.3 : 1
4.8 : 1
9 : 1
2 : 1
±
MeI
EtI
BuI
74
75
76
77
78
79
Me
Et
Bu
CH
Bn
CH
85
70
37
95
89
86
74
85
87
86
91
CH
BnBr
ClCH
2
ˆCHCH
2
Br
2
CHˆCH
2
2
NHCOPh
2
NHCOPh
c
Cyclohex-2-enyl bromide
Methyl acrylate
tert-Butyl acrylate
Acrylonitrile
80 )
cyclohex-2-en-1-yl
81
82
83
84
CH
CH
CH
CH
2
CH
2
CH
2
CH
2
CH
2
2
2
2
CO
CO
CN
2
t
Me
4 : 1
> 95 : 5 )
4 : 1
d
2
Bu
Methyl vinyl ketone
COMe
2 : 1
a) The two diastereoisomers were separated using chromatographic methods. b) The diastereoselectivity was
c
d
determined by HPLC (LiChrosorb). ) Not separated. ) Only one diastereoisomer was detected in the
1
H-NMR spectrum of the crude product.
Scheme 12
Electrophile
CH
ˆCHCH
BnBr
Cyclopent-2-enyl bromide
Cyclohex-2-enyl bromide
tert-Butyl acrylate
Producta)
R
Yield [%]
drb)
2
2
Br
85
86
87 )
CH
Bn
2
CHˆCH
2
62
81
64
76
89
85
2.3 : 1
5.5 : 1
±
±
c
cyclopent-2-en-1-yl
cyclohex-2-en-1-yl
CH
CH
c
88 )
t
d
89
90
2
CH
CH
2
CO
CN
2
Bu
> 95 : 5 )
Acrylonitrile
2
2
4 : 1
a) The two diastereoisomers were separated using chromatographic methods. b) The diastereoselectivity was
c
d
determined by HPLC (LiChrosorb). ) Not separated. ) Only one diastereoisomer was detected in the
1
H-NMR spectrum of the crude product.
For the benzylation of 6, we showed that the variation of solvent and base has a
dramatic effect on the selectivity. As can be seen in Scheme 13, using the same base but
changing the solvent, the selectivity could be increased. Changing the solvent from
THF to CH Cl /DMPU, the selectivity rose from 5.3 :1 to more than 9 :1. A reversal of
2
2

Helvetica Chimica Acta ± Vol. 81 (1998)
1857
Fig. 1. X-Ray crystal structure of the pentapeptide derivative 86a. O-Atoms in red, N-atoms in blue. The
structure was determined by P. B. Rheiner.
the selectivity was observed by changing the base: using BuLi as base, the pentapeptide
6
was benzylated to give preferentially product 86b with (R)-configuration on the new
stereogenic center (up to 1:6); on the other hand, deprotonation with t-BuOK and
benzylation led preferentially to the product (9 :1) of (S)-configuration.
Scheme 13
a
Solvent
Base
Yield [%]
Ratio ) (S)/(R)
THF
THF
THF
THF/DMPU
THF/DMPU
THF/DMPU
t-BuOK
LDA
BuLi
t-BuOK
t-BuOLi
BuLi
t-BuOK
BuLi
82
73
78
72
91
77
78
90
65
90
5.3 : 1
1 : 1
1 : 2.3
4.5 : 1
4 : 1
1 : 2
4.3 : 1
1 : 6
20 : 3
20 : 3
20 : 3
20 : 3
20 : 3
20 : 3
20 : 3
Et
Et
2
O/DMPU
O/DMPU
2
CH
CH
2
Cl
Cl
2
/DMPU
/DMPU
t-BuOK
BuLi
9.2 : 1
1 : 1.5
2
2
a) The diastereoselectivity was determined by HPLC (LiChrosorb; hexane/i-PrOH 97: 3).

1858
Helvetica Chimica Acta ± Vol. 81 (1998)
The pentapeptide 7 was added, in a Michael fashion, to tert-butyl acrylate ( !91)
1
applying the same conditions mentioned above. According to H-NMR analysis of the
crude product, the derivative 91 was obtained as a single diastereoisomer of unknown
configuration (Scheme 14).
Scheme 14
For the solubilization of the heptapeptide 8 in THF, at least 30 equiv. of LiBr were
necessary. The solution thus obtained was then treated with base (t-BuOK) and
electrophile under the standard conditions. The results are summarized in Scheme 15.
The products, 92 ± 95, were isolated in high yields. The selectivities were in the same
range as found for the pentapeptide derivatives. Again, the reaction with tert-butyl
acrylate gave a single diastereoisomer (95 of unknown configuration) as determined by
HPLC analysis.
Scheme 15
Electrophile
Product
R
Yield [%]
dr
Allyl bromide
Acrylonitrile
Methyl vinyl ketone
tert-Butyl acrylate
92
93
94
95
CH
CH
CH
CH
2
2
2
2
CHˆCH
2
52
86
75
85
6.2 : 1
3 : 1
4 : 1
CH
CH
CH
2
2
2
CN
COMe
t
CO
2
Bu
> 95 : 5
Finally, the Aca-containing tripeptide 4 could be deprotonated and alkylated using
the same conditions optimized for the aminomalonate cases. As can be seen from
Scheme 16, the products, 96 ± 100, were obtained in very good yields, albeit as 1 :1
mixtures of epimers (four stereoisomers of 99). Compared to the aminomalonate
derivatives, the epimer pairs could be separated by flash chromatography much more
readily. The configuration of the products was not determined.

Helvetica Chimica Acta ± Vol. 81 (1998)
1859
Scheme 16
Electrophile
MeI
Producta)
R
Yield [%]
96
97
98
Me
CH
Bn
82
74
67
70
88
CH
BnBr
2
ˆCHCH
2
Br
2
CHˆCH
2
b
Cyclohex-2-enyl bromide
tert-Butyl acrylate
99 )
cyclohex-2-en-1-yl
CH
t
100
2
CH
2
CO
2
Bu
a) 1 : 1 Mixture of two diastereoisomers, readily separated. b) Four isomers were detected by H-NMR; not
separated.
1
4
. Removal of the Electron-Withdrawing Groups (CO R and CN). ± According to
2
Scheme 2, the last step on the way to modified peptides is the removal of the activating
group. In the classical malonic-ester syntheses, this has been traditionally effected via a
two-step procedure: cleavage of the ester group, followed by thermal decarboxyl-
9
ation of the acid formed ). For the cases at hand, we proceeded as follows: the benzyl-
ester groups of the derivatives of benzyl malonates 2 and 6 were smoothly cleaved
by hydrogenolysis (H /Pd-C/MeOH); the tert-butyl-ester groups of the tert-butyl
2
malonates derived from 3 or 5 were readily removed with HCl in Et O. No spontaneous
2
decarboxylation was observed, and the acids formed are stable and can be stored for
several days without any decomposition. Without further purification, the acids were
then decarboxylated using 2 equiv. of LiBr and catalytic amount of pyridine in THF
under reflux. Other methods such as radical decarboxylation, following Bartonꢁs [19] or
Kochiꢁs procedure [20], failed completely.
As can be seen from the data presented in Schemes 17 and 18, the tripeptide
derivatives 101 ± 106 and the pentapeptide derivatives 107 ± 115 were cleaved and
decarboxylated in high yields, using the above-mentioned two-step procedure. The new
peptide derivatives were formed as 1 :1 mixtures of epimers. No side reactions of any
functionality and no epimerization of the other stereogenic centers were detectable. In
most cases, the isomers could be separated chromatographically. The configuration of
the central amino-acid residue was determined by derivatization and gas chromatog-
raphy following Bayerꢁs procedure [21] (see Exper. Part).
The use of an allylic ester group in the Ama side chain opens an alternative route for
the removal of the activating group. Tsuji and co-workers reported a simple one-step
method for the conversion of substituted allyl malonates to monocarboxylic acids and
9)
Another method for the dealkoxycarbonylations of malonates has been reviewed by Krapcho. This
process involves the use of H O, H O with added salts, or anhydrous salts in dipolar aprotic media such as
2
2
DMSO [17]. In addition, Ho reported that malonates can be converted to carboxylic acids by treatment
with (iodo)trimethylsilane [18]. Both procedures are carried out at rather high temperatures (ꢀ 1008).

1860
Helvetica Chimica Acta ± Vol. 81 (1998)
Scheme 17
Methoda)
Educt
Productb)
PG
R
Yield [%]
A
A
A
B
B
B
60
61
62
69
70
71
101
102
103
104
105
106
Boc
Boc
Boc
Ac
Ac
Ac
Me
CH
cyclohexyl
CH
CH
CH
76
91
81
94
84
96
2
2
CH Me
2
2
2
CHˆCH
2
Ph
2 2 3
CH CO CMe
a) Method A: i) Pd/C, H
HCl/Et
products 104 ± 106 separated by FC.
, MeOH, 4 ± 10 h; ii) 2 equiv. LiBr, cat. pyridine, THF, D, 6 ± 10 h. Method B: i) sat.
O, 10 h; ii) 2 equiv. LiBr, cat. pyridine, THF, D, 6 ± 10 h. ) 1 : 1 Mixture of two diastereoisomers;
2
b
2
Scheme 18
Methoda)
Educt
PG
Productb)
R
Yield [%]
A
A
A
A
B
B
B
B
B
85
86
89
90
74
75
77
79
84
Boc
Boc
Boc
Boc
Z
Z
Z
Z
Z
107
108
109
110
111
112
113
CH
CH
CH
CH
Me
Et
2
2
2
2
CH
Ph
CH
CH
2
Me
76
74
87
74
87
79
78
74
85
2
2
CO
CN
2 3
CMe
CH
CH
CH
2
2
2
CHˆCH
NHCOPh
CH COMe
2
c
114 )
115
2
a) Method A: i) Pd/C, H
, MeOH, 4 ± 10 h; ii) 2 equiv. LiBr, cat. pyridine, THF, D, 6 ± 10 h. Method B: i) sat.
2
b
HCl/Et
2
O, 10 h; ii) 2 equiv. LiBr, cat. pyridine, THF, D, 6 ± 10 h. ) 1 : 1 Mixture of two diastereoisomers;
c
readily separated by FC. ) Not separated.
esters in the presence of a Pd catalyst under mild conditions [22]. The treatment of the
0
allylic-ester derivative 91 with tertiary amine salts of HCO H, catalyzed by Pd -
2
phosphine complex at r.t. leads to evolution of CO2 and propene, giving the

Helvetica Chimica Acta ± Vol. 81 (1998)
1861
decarboxylated peptide derivative 109 in high yield (Scheme 19). Better results were
0
II
achieved by the in situ generation of the Pd -phosphine complex starting from Pd
0
(
Method A in Scheme 19: Pd(OAc) , PPh ), as compared to the use of pre-formed Pd -
2 3
phosphine complex (Method B). Again, the peptide derivative was formed as a 1 :1
mixture of separable isomers in both cases. No further attempts were made to optimize
this reaction.
Scheme 19
91
Method A:
Method B:
5 % Pd(PPh3)4,
5
% Pd(OAc)2, 10 % PPh3
3
equiv. HCOOH, 3 equiv. Et3N
3 equiv. HCOOH, 3 equiv. Et3N
O
O
O
H
N
H
H
N
N
109 (90%; dr 1:1)
109 (75%; dr 1:1)
Boc
N
N
O
H
H
H
O
O
t
O
O Bu
Finally, the decyanation of the Aca-containing peptide derivative 97 could be
achieved, using a procedure published by Rychnovsky et al. [23] (Scheme 20): a solution
1
0
of 97 in THF was added to a solution of Na in liquid NH at � 788 ). In addition to the
3
decyanation, an amidation of the C-terminal methyl-ester group occurred under these
conditions, and the peptide amide 116 was formed, in good yield, as a 1 : 1 mixture of
diastereoisomers.
Scheme 20
10)
It was reported that the reaction of tertiary mononitriles with solvated electrons produces exclusively the
corresponding hydrocarbon. Whereas the primary and the secondary nitriles not only undergo cleavage of
the C� CN bond but also reduction to the amine, the reaction of tridecanenitrile with Li in EtNH
2
gives a
2
:1 mixture of the corresponding hydrocarbon and the amine [24].

1862
Helvetica Chimica Acta ± Vol. 81 (1998)
5
. Structure Analysis of the Ama- and Aca-Containing Peptides. ± The structure of
the peptides with CO R and CN substituents, as shown in the Schemes 7±16, is compatible
2
with all spectroscopic data given in the Exper. Part. When possible and appropriate, the
peptides were also submitted to elemental analysis and degradation to their components,
followed by GC analysis on chiral columns [21]. As mentioned in the previous sections,
the configurations at the CO R- and CN-substituted stereogenic centers is unknown in
2
almost all cases. There was not enough time, within the present investigation, to do ex-
tensive structural work by NMR and CD spectroscopy, or by X-ray analysis (few of the
new compounds were actually crystalline!). Thus, we mention here only two examples.
The CD spectroscopy has been used successfully to investigate the secondary
structure of peptides and proteins in solution: characteristic troughs between 200 and
2
30 nm in the CD spectra of peptides are associated with b-sheet and a-helix secondary
structures, respectively [25]. An overlay of the CD spectra of the pentapeptides 86a and
6b in 2,2,2-trifluoroethanol (TFE) at 0.2 mm concentration in shown in Fig. 2,a: both
8
CD curves are typical for peptides with no defined secondary structure [25]. In
contrast, the CD spectrum of the heptapeptide derivative 95 in TFE shows two
4
characteristics: a shoulder at 220 nm ([q] ˆ� 4.0 ´ 10 ) and a strong minimum at 206 nm
4
(
[q] ˆ� 6.8 ´ 10 ); as can be seen from Fig. 2,b, the use of MeOH instead of TFE does
not change the general pattern of the CD spectrum of 95. The CD curves observed for
9
9
5 indicate the presence of a defined secondary structure. The conclusion would be that
5 has a 3 -helical structure [26][27]. This is in contrast to ꢀnormalꢁ peptides of which
1
0
distinct secondary structures are observed in solution only when they are built of
11
1
0 ± 15 amino-acid residues ). In fact, 95 contains a geminally disubstituted central
amino acid, and these are known to be helix-inducing!
Fig. 2. CD Spectra of two Ama-containing peptides. a) Overlay of the CD spectra (molar ellipticity [q] in 10 deg
2
� 1
cm mol ) of the epimeric pentapeptides 86a (Ð) and 86b (---) in 2,2,2-trifluoroethanol (TFE) at 0.2 mm
concentration. b) Overlay of the CD spectra of the heptapeptide 95 in MeOH (red) and TFE (black) at 0.2 mm
concentration.
11)
Exceptions to this rule are observed i) with peptides containing proline or other turn-inducing amino acids
28], ii) with peptides containing several or only a,a-disubstituted amino acids (e.g., Aib) [30], and iii) with
homopeptides, consisting of sequences of the same amino acid [31].
[

Helvetica Chimica Acta ± Vol. 81 (1998)
1863
An X-ray crystal-structure analysis of Boc-Val-Leu-(CO Bn)Phe-Abu-Ile-OMe
2
(
86a) was possible: this pentapeptide derivative gave crystals from MeOH suitable for
X-ray analysis (Fig. 1). The compound forms a perfect right-handed 3 -helix, stabilized
10
by two intramolecular CˆO ´´´ H� N H-bonds. As deduced from the CD spectrum
above (Fig. 2,a), there can be little of this conformation in solution.
6
. Discussion of the Results and Conclusions. ± The readily prepared N-Boc- or N-
Z-protected amino-malonic acid half-esters 9 ± 12 (PG-NH-CH(CO R)-CO HꢁPG-
2
2
Ama-OH) and the related (amino)(cyano)acetic acid 15 (Boc-NH-CH(CN)-
CO HꢁBoc-Aca-OH) can be used as building blocks in conventional peptide solution
2
synthesis (without special modifications of the usual coupling and handling proce-
dures). This was demonstrated by incorporation of the Ama and Aca residues in the
central positions of tri-, penta-, and heptapeptides 1 ± 8. There is no doubt ± in our
minds ± that these residues could be incorporated in other positions along peptide
chains (Scheme 21). The resulting Ama-containing peptides can then be alkylated
under mildly basic conditions by primary alkyl halides, by primary and secondary allyl
halides, by N-(chloromethyl) amides, and by Michael acceptors (such as acrylates,
acrylonitriles, or nitroolefins). By this peptidic backbone alkylation, a tertiary
stereogenic center is introduced, and the new side-chain may be a simple alkyl group,
or it may be functionalized (CˆC bond, ester, CN, amino, NO group); there are
2
hundreds of possible electrophiles commercially available (just skim through a fine-
chemicals catalog!). The products of alkylation are often formed with high
diastereoselectivity (Schemes 8 ± 15), and the geminally disubstituted Ama residue in
the peptide chain appears to exhibit the well-known helix-inducing effect (Figs. 1 and
2
). Depending upon the type of Ama ester group, deprotection by hydrogenation
(
CO Bn), by treatment with acid (CO (t-Bu)) or with Pd(PPh ) /formate (CO Allyl)
2
2
3
4
2
leads to the free carboxylic acids (lower homologs of a-branched aspartic-acid residues
in the peptide chain), which are remarkably resistant to loss of CO (!), or to the
2
decarboxylated peptides with the electrophilically introduced side chain at the former
Ama position (Schemes 17 ± 19). Thus, three types of modified peptides become
available: those with various branched Ama ester residues, the corresponding acids,
and conventional peptides with one non-proteinogenic residue of l- and d-config-
uration. Furthermore, we have demonstrated that peptides with geminal substitution by
a CN and an alkyl group at one of the residues (of (R)- and (S)-configuration) can be
readily prepared. Of course, it should also be possible to incorporate more than one
Ama and/or Aca residue at various positions of a peptide. Finally, we are confident that
solid-phase peptide synthesis is feasible with the Boc-Ama and Boc-Aca derivatives
described herein. Thus, a highly combinatorial approach to the synthesis of new types of
modified peptides is at hand!
A comparison of the Ama/Aca strategy (A) with our previous method (B) of
polylithiated peptide back-bone modification (Scheme 1) reveals the following
similarities and differences, and relative advantages and disadvantages. i) For both
methods, a peptide with a special amino acid (Ama, Aca for A, N-methyl-amino acid(s)
for B [4]) has to be prepared. ii) A peptide with a single side chain is formed directly in
B, and only after two additional steps, i.e., ester cleavage and decarboxylation or
decyanation in A. iii) On the other hand, in the new method A, the ester, acid, and

1864
Helvetica Chimica Acta ± Vol. 81 (1998)
Scheme 21
nitrile intermediates are interesting modified peptides of their own. iv) After removal
of the acidifying CO R or CN groups in method A, 1:1 mixtures ± albeit readily
2
separable ± of diastereoisomeric peptides are obtained, while there is usually rather
high stereoselectivity of alkylations with polylithiated peptides in B. v) The greatest
advantage of the new method are the much milder conditions and less expensive
reagents for the alkylation step: 1 equiv. or catalytic amounts of a Na or K alkoxide
base at room temperature for A vs. many equiv. of a Li base (LiNR or t-BuLi) at dry-ice
2
temperature for B!
Experimental Part
1
. Abbreviations. Abu: (R)-2-aminobutyric acid; Ama: aminomalonic acid, Aca: (amino)(cyano)acetic
acid, Boc O: di(tert-butyl)dicarbonate, DCC: dicyclohexylcarbodiimide, DIPA: diisopropylamine, EDC: 1-[3-
dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride, FC: flash chromatography, HOBt: 1-hydroxy-1H-
2
(
benzotriazole), NMM: N-methylmorpholine, TMEDA: N,N,N',N'-tetramethylenediamine; three-letter amino-
acid abbreviations are used for a-amino acids.
2
. General. THF used for carboxylation and coupling reactions was freshly distilled over K under Ar. DIPA
and TMEDA were distilled from CaH . Solvents for chromatography and for workup were distilled over P O .
2
2 5
Amino-acid derivatives were purchased from Senn, Bachem, and Degussa. BuLi was used as a 1.5m soln. in
hexane. All other chemicals for reactions were used as purchased from Fluka. TLC: Merck silica gel 60 F254 anal.
plates: detection with UV and by placing in a Cl
2
tank for 5 min, then staining with a soln. of N,N,N',N'-
tetramethyl-4,4'-methylenebis[aniline]. FC: Merck silica gel 60 (40 ± 63 mm). GC: Chirasil-Val ꢂ column
(
(
Macherey-Nagel, 25 m, 0.4 mm); Carlo-Erba-Fractovap 4160-HRGC; injector temp. 2208; detector temp. 2208
FID); carrier gas: 0.5 bar H ; temp. program: 3 min 858, 48/min until 1808. Anal. HPLC: Kontron HPLC
2
system; UV detector Uvikon LCD-75, programmer 200, integrator Shimadzu C-R 1B Chromatopak;
LiChrosorb Si-60 column (Knauer 7 mm, 250 Â 4 mm). Prep. HPLC: Knauer HPLC system; pump type 64,
programmer 50, UV detector variable-wavelength monitor, LiChrosorb Si-60 column (Knauer 7 mm, 250 Â
35 mm). Optical rotation: Perkin-Elmer-241 polarimeter (10 cm, 1 ml cell). Circular dichroism (CD): Jasco
J-710; recording from 190 to 250 nm at r.t.; 1-mm cell; average of 5 scans, corrected for the baseline; peptide
2
� 1
concentration 0.2 mm; molar ellipticity q in deg ´ cm ´ dmol (l in nm); smoothing by Jasco software. M.p.:

Helvetica Chimica Acta ± Vol. 81 (1998)
1865
Büchi 510; uncorrected. 1H-NMR: Bruker-AMX-II-500 (500 MHz), -AMX-400 (400 MHz), -AMX-300
13
(
-
300 MHz), or Varian-Gem-200 (200 MHz) spectrometer. C-NMR: Bruker-AMX-II-500 (125 MHz),
AMX-400(100 MHz), -AMX-300 (75 MHz), or Varian-Gem-200 (50 MHz) spectrometer. Signals of epimers
in italics. MS: VG ZAB2-SEQ spectrometer (FAB).
. General Procedures. 3.1. Carboxylation of Glycine Derivatives (GP 1): To a soln. of DIPA (2.2 equiv.) and
3
TMEDA (2.2 equiv.) in THF, BuLi (2.2 equiv.) was added at � 788 (dry ice). After 30 min stirring, a soln. of the
glycine derivative (1 equiv.) in THF was added slowly (Tꢂ� 708), and stirring was continued for 1 h at � 788.
2
Then, CO was bubbled into the mixture through a needle for 1 h. The cooling bath was removed after 10 min,
because the soln. became thick. The mixture was allowed to warm to r.t. and acidified to pH 1 with 1n H
soln. The two layers were separated, and the aq. layer was extracted twice with Et O. The combined org. layers
), filtered, and evaporated. The obtained Ama-acid derivatives were used without further
2 4
SO
2
were dried (MgSO
purification.
4
3
.2. Coupling with Isobutyl Chloroformate (GP 2). To a soln. of the carboxy component (1 equiv.) in dry
THF, NMM (1 equiv.) and isobutyl chloroformate (1 equiv.) were added at � 158. After 10 min, a cold (08) soln.
of the salt of the amino component (1 equiv.) and NMM (1 equiv.) in THF and DMF was added dropwise (Tꢂ
�
108). After 30 ± 60 min, the cooling bath was removed, and the soln. was warmed to r.t. Stirring was continued
for 12 h. The mixture was then diluted with AcOEt and washed with 5% citric acid, sat. aq. NaHCO
NaCl soln. All aq. layers were additionally extracted twice with AcOEt. The combined org. layers were dried
MgSO ), filtered and evaporated.
.3. Coupling with DCC (GP 3). To a soln. of the carboxy component (1 equiv.) and the salt of the amino
component (1 equiv.) in THF at 08, NMM (2 equiv.) was added. After 15 min, HOBt (1.1 equiv.) and DCC
1.1 equiv.) were added successively. After 1 h, the mixture was allowed to warm to r.t., and stirring was
continued for 12 h. Then, the white precipitate was filtered off. Workup of the filtrate according to GP 2.
.4. Coupling with EDC (GP 4). A stirred soln. of the amino-ester hydrochloride (1 equiv.) in THF under
3
, and sat. aq.
(
4
3
(
3
Ar was treated with NMM (1 equiv.) at 08 (ice bath). This mixture was added to a soln. of the carboxy
component (1 equiv.) in THF and DMF. Then, HOBt (1.2 equiv.) and EDC (1.2 equiv.) were added successively.
The mixture was allowed to warm at r.t., and stirring was continued for 12 h. Workup according to GP 2.
4
. Synthesis of the Starting Materials. 4.1. Synthesis of Boc-Leu-Ama(OMe)-Leu-OMe (1). Boc-Gly-OMe. A
colorless soln. of 20.0 g (115 mmol) of Boc-Gly-OH in 100 ml of Et O was treated with a soln. of CH , until
was destroyed by adding AcOH. Drying (MgSO ) and evaporation gave
): 1.46 (s, 9 H); 3.75 (s, 3 H); 3.92 (d, J ˆ 7, 2 H);
): 28.32 (Me); 42.30 (CH ); 52.24 (Me); 80.02 (C); 155.73 (C);
2
2 2
N
the soln. became yellow. Excess CH
2
N
2
4
1
2
5
1
1.6 g (quant.) of Boc-Gly-OMe. H-NMR (200 MHz, CDCl
.08 (m, 1 H). C-NMR (100 MHz, CDCl
70.87 (C). FAB-MS: 190 (1, [M ‡ 1] ), 134(23), 90(13), 67(100).
3
1
3
3
2
‡
Boc-Ama(OMe)-OH (9). According to GP 1, with DIPA (24.4 ml, 172 mmol), TMEDA (25.82 ml,
172 mmol), and BuLi (118.6 ml, 172 mmol) in THF (300 ml), and Boc-Gly-OMe (15.0 g, 85.7 mmol) in THF
(
100 ml). After workup 19.9 g (quant.) of 9 were obtained. Colorless oil. Used without further purifications.
1
3
H-NMR (200 MHz, CDCl ): 1.45 (s, 9 H); 3.8 (s, 3 H); 4.8, 5.0 (2 br. s, 1 H); 5.7 (br. m, 1 H); 7.7 (br. m, 1 H).
Boc-Ama(OMe)-Leu-OBn (16). According to GP 3, with 9 (19.9 g, 85.7 mmol), TsOH ´ H-Leu-OBn
(
34.48 g, 87.5 mmol), HOBt (13.41 g, 85.7 mmol), NMM (9.64 ml, 85.7 mmol), and DCC (18.97 g, 91.5 mmol)
1
in THF (250 ml) and DMF (60 ml). FC (hexane/AcOEt 3 : 2): 30.85 g (73%) of 16. White foam. H-NMR
(
(
6
(
400 MHz, CDCl
3
; 2 epimers): 0.88 ± 0.95 (m, 6 H); 1.44, 1.45 (2s, 9 H); 1.54 ± 1.69 (m, 3 H); 3.74, 3.79
2s, 3 H); 4.60 ± 4.68 (m, 1 H); 4.89 ± 4.91 (m, 1 H); 5.11 ± 5.19 (m, 2 H); 5.79 ± 5.85 (m, 1 H); 6.86, 6.91 (2d, J ˆ
1
3
.5, 8.0, 1 H); 7.29 ± 7.39 (m, 5 H). C-NMR (100 MHz, CDCl
Me); 24.77, 24.81 (CH); 28.21, 28.31 (Me); 41.12, 41.33 (CH ); 51.35 (CH); 53.17, 53.21 (Me); 57.75, 57.85
CH); 67.20 (CH ); 80.00, 80.70 (C); 126.95, 127.54 (CH); 128.24, 128.47 (CH); 128.51, 128.62 (CH); 135.23
3
; 2 epimers): 21.77, 21.79 (Me); 22.76, 22.80
2
(
(
2
C); 155.23, 155.73 (C); 164.82, 164.91 (C); 168.00, 168.11 (C); 171.97, 172.01 (C).
H-Ama(OMe)-Leu-OBn ´ HCl (17 ´ HCl). To a soln. of 16 (15.0 g, 34.37 mmol) in Et
2
O (30 ml), a sat. HCl/
Et
7 ´ HCl were obtained. Yellow foam. H-NMR (200 MHz, CDCl
m, 3 H); 3.74, 3.82 (2s, 3 H); 4.50 ± 4.63 (m, 1 H); 5.05 ± 5.25 (m, 3 H); 5.64 ± 5.78 (m, 1 H); 7.27 ± 7.43
2
O soln. (100 ml) was added, and the mixture was stirred at r.t. for 12 h. After evaporation 13.24 g (quant.) of
1
1
3
; 2 epimers): 0.81 ± 0.95 (m, 6 H); 1.55 ± 1.75
(
(
1
‡
‡
m, 5 H); 7.5, 8.0 (2d, J ˆ 8, 1 H); 9.0 (br. m, 3 H). FAB-MS: 359 (1, [M ‡ 23] ), 337 (100, [M ‡ 1] ), 201 (9),
78 (7).
Boc-Leu-Ama(OMe)-Leu-OBn (18). According to GP 2 with 17 ´ HCl (11.5 g, 34.2 mmol), Boc-Leu-OH ´
O (8.72 g, 35 mmol), HOBt (4.73 g, 35 mmol), NMM (3.85 ml, 35 mmol), and DCC (8.3 g, 40 mmol) in THF
200 ml); 2 h at 08 and 20 h at r.t. FC (hexane/AcOEt 1 : 1): 13.34 g (82%) of 18. White foam. 1H-NMR
400 MHz, CDCl ; 2 epimers): 0.88 ± 0.95 (m, 12 H); 1.45 (s, 9 H); 1.56 ± 1.72 (m, 6 H); 3.75, 3.79 (2s, 3 H);
H
(
(
2
3

1866
Helvetica Chimica Acta ± Vol. 81 (1998)
4
.15 ± 4.20 (m, 1 H); 4.57 ± 4.66 (m, 1 H); 4.82, 4.89 (2d, J ˆ 7.5, 6.5, 1 H); 5.09 ± 5.20 (m, 3 H); 6.93, 7.04
13
(
2d, J ˆ 8.0, 7.5, 1 H); 7.23 ± 7.41 (m, 6 H). C-NMR (100 MHz, CDCl
2.75 (Me); 23.00, 23.03 (Me); 24.77 (CH); 24.81 (CH); 28.28 (Me); 40.89 (CH
CH); 53.05 (CH); 53.22, 53.33 (Me); 56.49, 56.58 (CH); 67.20 (CH ); 80.29 (C); 126.99, 127.63 (CH); 128.26,
28.31 (CH); 128.62, 128.64 (CH); 135.23, 135.32 (C); 155.57 (C); 164.25, 164.69 (C); 167.34, 167.42 (C); 171.86,
3
; 2 epimers): 21.72 (Me); 21.77 (Me);
2
(
1
1
3
2
); 41.22 (CH ); 51.43, 51.36
2
2
‡
‡
71.93 (C); 172.78, 172.90 (C). FAB-MS: 672 (39, [M ‡ 23] ), 550 (27, [M ‡ 1] ), 494(34), 451(29), 450(91),
37(92), 222(29), 176(41), 91(100).
Boc-Leu-Ama(OMe)-Leu-OH (19). A suspension of 18 (10.66 g, 19 mmol), and 10% Pd/C (0.5 g) in
MeOH (40 ml) was stirred at r.t. under H
2
(balloon) for 12 h. Filtration (Celite) and evaporation gave 8.94 g
; 2 epimers): 0.92 ± 0.96 (m, 12 H); 1.45 (s, 9 H); 1.63 ±
1
(quant.) of 19. White foam. H-NMR (500 MHz, CDCl
3
1
7
2
5
.75 (m, 6 H); 3.49 (s, 3 H); 4.13, 4.28 (2m, 1 H); 4.57 ± 4.62 (m, 1 H); 5.02 ± 5.15 (m, 1 H); 5.32 (d, J ˆ 6.0, 1 H);
13
.15, 7.22 (2d, J ˆ 7.0, 7.9, 1 H); 7.50 ± 7.55 (br. m, 1 H). C-NMR (125 MHz, CDCl
1.78 (Me); 22.85 (Me); 24.02 (Me); 24.74 (CH); 24.85 (CH); 28.28 (Me); 40.95 (CH
1.38 (CH); 53.11, 53.40 (Me); 56.56, 56.72 (CH); 164.63 (C); 167.43 (C); 173.22 (C); 174.78 (C). FAB-MS: 482
3
; 2 epimers): 21.74 (Me);
2
); 41.30 (CH ); 51.26,
2
‡
‡
(
20, [M ‡ 23] ), 460 (6, [M ‡ 1] ), 404(15), 360(35), 247(54), 132(20), 86(100).
Boc-Leu-Ama(OMe)-Leu-OMe (1). A soln. of 19 (8.94 g, 19 mmol) in Et O (150 ml) was treated with
2
CH
2
N
2
until the soln. became yellow. Excess CH
2
N
2
was destroyed by adding some drops of AcOH. Drying
1
(
(
MgSO
4
) and evaporation gave 8.97 g (quant.) of 1. H-NMR (300 MHz, CD
3
OD; 2 epimers): 0.88 ± 0.96
m, 12 H); 1.43, 1.44 (2s, 9 H); 1.48 ± 1.72 (m, 6 H); 3.70 (s, 3 H); 3.75, 3.77 (2s, 3 H); 4.13 ± 4.17 (br. m, 1 H);
.44 ± 4.49 (m, 1 H); 4.55 ± 4.9 (br. m, 1 H). 13C-NMR (75 MHz, CD
3.39 (Me); 25.80 (CH); 28.66 (Me); 41.39 (CH ); 41.73 (CH ); 52.49 (Me); 52.72 (CH); 53.49 (Me); 54.50
4
2
3
OD; 2 epimers): 21.59, 21.78 (Me); 23.22,
2
2
(CH); 57.68 (CH); 158.15 (C); 167.43 (CH); 168.86 (C); 174.07, 174.21 (C); 175.81 (C).
4
.2. Synthesis of Boc-Leu-Ama(OBn)-Leu-OMe (2). Boc-Ama(OBn)-OH (10). According to GP 1, with
DIPA (22.67 ml, 160 mmol), TMEDA (24.02 ml, 160 mmol), and BuLi (106.6 ml, 160 mmol) in THF (300 ml),
and Boc-Gly-OBn (20.7 g, 78.5 mmol) in THF (100 ml). After workup, 25.3 g (quant.) of 10 were obtained.
1
Colorless oil. Used without further purification. H-NMR (200 MHz, CDCl
3
): 1.45 (m, 9 H); 4.8 ± 4.9 (m, 1 H);
5
.05 (d, J ˆ 10, 1 H); 5.2 ± 5.46 (m, 2 H); 5.6 ± 5.7 (m, 1 H); 7.25 ± 7.4 (m, 5 H).
Boc-Ama(OBn)-Leu-OMe (20). According to GP 3, with 10 (23.4 g, 78 mmol), TsOH ´ H-Leu-OMe
(
(
25.39 g, 80 mmol). NMM (8.81 ml, 80 mmol), and DCC (17.33 g, 85 mmol) in THF (300 ml) and DMF
1
100 ml). FC (hexane/AcOEt 2 : 1): 20.31 g (60%) of 20. Colorless oil. H-NMR (400 MHz, CDCl
3
; 2 epimers):
0
.84 ± 0.96 (m, 6 H); 1.42, 1.43 (2s, 9 H); 1.47 ± 1.67 (m, 3 H); 3.69, 3.71 (2s, 3 H); 4.54 ± 4.61 (m, 1 H); 4.93 ±
.97 (m, 1 H); 5.17 ± 5.28 (m, 2 H); 5.83 (d, J ˆ 6.5, 1 H); 6.83, 6.90 (2d, J ˆ 7.9, 7.5, 1 H); 7.31 ± 7.38 (m, 5 H).
4
13
C-NMR (100 MHz, CDCl
3
; 2 epimers): 21.73, 21.78 (Me); 22.69, 22.78 (Me); 24.70, 24.74 (CH); 28.21, 28.30
); 80.60 (C);
(
Me); 41.16, 41.42 (CH ); 51.16, 51.25 (CH); 52.34, 52.38 (Me); 57.95 (CH); 68.05, 68.15 (CH
2
2
1
1
26.94, 127.48 (CH); 128.42, 128.47 (CH); 128.61, 128.65 (CH); 134.77 (C); 155.16 (C); 164.59 (C); 167.48,
67.59 (C); 172.51, 172.59 (C).
2
H-Ama(OBn)-Leu-OMe ´ HCl (21 ´ HCl). To a soln. of 20 (9.00 g, 19.15 mmol) in 30 ml of Et O, a sat. HCl/
Et
2
O soln. (125 ml) was added, and the mixture was stirred at r.t. for 12 h. After evaporation, 7.01 g (quant.) of
1
21 ´ HCl were obtained. Yellow foam. H-NMR (200 MHz, CDCl
3
): 0.80 ± 1.00 (m, 6 H); 1.50 ± 1.70 (m, 3 H);
3.60 (s, 3 H); 3.80 ± 4.00 (m, 1 H); 4.35 ± 4.50 (m, 1 H); 5.15 ± 5.35 (m, 2 H); 5.65 ± 5.85 (m, 1 H); 7.20 ± 7.45
(
m, 5 H); 8.25 ± 9.00 (br. m, 3 H).
2
Boc-Leu-Ama(OBn)-Leu-OMe (2). According to GP 2, with 20 (14.68 g, 41 mmol), Boc-Leu-OH ´ H O
(
11.03 g, 45 mmol), NMM (5.04 ml, 45 mmol), and isobutyl chloroformate (5.98 ml, 45 mmol) in THF (300 ml).
1
FC (hexane/AcOEt 3 : 1): 15.03 g (67%) of 2. H-NMR (400 MHz, CDCl
3
; 2 epimers): 0.84 ± 0.94 (m, 12 H);
1
(
.43, 1.44 (2s, 9 H); 1.45 ± 1.80 (m, 6 H); 3.69, 3.71 (2s, 3 H); 4.10 ± 4.29 (m, 1 H); 4.52 ± 4.58 (m, 1 H); 4.84, 4.93
2d, J ˆ 8.8, 8.8, 1 H); 5.11 ± 5.27 (m, 3 H); 6.80 ± 6.90 (m, 1 H); 7.15 ± 7.25 (m, 1 H); 7.28 ± 7.38 (m, 5 H).
3
1
C-NMR (100 MHz, CDCl
CH); 24.74 (CH); 28.26, 28.27 (Me); 41.07, 41.20 (CH
Me); 52.95, 53.08 (CH); 56.66, 56.74 (CH); 68.22, 68.33 (CH
28.64 (CH); 128.68 (CH); 134.62, 134.67 (C); 155.55 (C); 164.15 (C); 166.79, 166.82 (C); 172.38, 172.50 (C);
3
; 2 epimers): 21.75 (CH
3
); 21.77 (Me); 22.67, 22.75 (Me); 22.98, 23.05 (Me); 24.71
); 41.33, 41.39 (CH ); 51.25, 51.36 (CH); 52.36, 52.40
); 80.16, 80.32 (C); 128.39, 128.50 (CH); 128.54,
(
(
1
1
2
2
2
‡
‡
72.76, 172.81 (C). FAB-MS: 572 (2, [M‡ 23] ), 550 (9, [M‡ 1] ), 494(12), 450(16), 337(18), 146(32), 91(100).
t
t
4
.3. Synthesis of Ac-Leu-Ama(O Bu)-Leu-OMe (3). Z-Ama(O Bu)-OH (12). According to GP 1, with
DIPA (15.4 ml, 108 mmol), TMEDA (16.21 ml, 108 mmol), and BuLi (75 ml, 108 mmol) in THF (300 ml), and
Z-Gly-OtBu (14.4 g, 54 mmol) in THF (100 ml). After workup, 16.9 g (quant.) of 12 were obtained. Colorless
1
oil. Used without further purification. H-NMR (200 MHz, CDCl
3
; 2 epimers): 1.35 ± 1.5 (br. m, 9 H); 4.8, 4.9
(2d, J ˆ 8, 8, 1 H); 5.15 (s, 2 H); 5.85, 6.9 (2d, J ˆ 8.0, 8.0, 1 H); 7.3 ± 7.4 (m, 5 H); 7.6 ± 7.8 (br. m, 1 H).

Helvetica Chimica Acta ± Vol. 81 (1998)
1867
t
Z-Ama(O Bu)-Leu-OMe (22). According to GP 3, with 12 (16.7 g, 54 mmol), TsOH ´ H-Leu-OMe
(
(
(
5
2
17.45 g, 55 mmol), HOBt (7.35 g, 55 mmol), NMM (6 ml, 55 mmol), and DCC (12.4 g, 60 mmol) in THF
200 ml). FC (hexane/AcOEt 3 : 1): 16.27 g (69%) of 22. 1H-NMR (300 MHz, CDCl
; 2 epimers): 0.8 ± 1.0
m, 6 H); 1.47, 1.50 (2s, 9 H); 1.5 ± 1.75 (m, 3 H); 3.72, 3.73 (2s, 3 H); 4.55 ± 4.7 (m, 1 H); 4.83 (d, J ˆ 7.0, 1 H);
3
.12 (s, 2 H); 5.95 (m, 1 H); 6.7 ± 6.85 (br. m, 1 H); 7.3 ± 7.45 (m, 5 H). 13C-NMR (75 MHz, CDCl
1.69, 21.81 (Me); 22.69 (Me); 24.67, 24.71 (CH); 27.70 (Me); 41.44, 41.52 (CH ); 51.09 (Me); 52.28, 52.39
3
; 2 epimers):
2
(
(
(
CH); 58.57, 58.72 (CH); 67.11 (CH
2
); 83.89, 84.22 (C); 127.87, 127.97 (CH); 128.09 (CH); 128.42 (CH); 136.05
‡
C); 155.84 (C); 161.43 (C); 165.84, 166.13 (C); 172.53, 172.57 (C). FAB-MS: 873 (3, [2M ‡ 1] ), 739(4), 459
‡
‡
5, [M ‡ 23] ), 437 (15, [M ‡ 1] ), 381(100), 336(11).
t
H-Ama(O Bu)-Leu-OMe (23). A suspension of 22 (16.0 g, 36.8 mmol) and 10% Pd/C (0.4 g) in MeOH
(
60 ml) was stirred under H
2
for 12 h at r.t. After filtration (Celite) and evaporation, 10.9 g (quant.) of 23 were
; 2 epimers): 0.85 ± 0.95 (m, 6 H); 1.46 (s, 9 H); 1.5 ± 1.7 (m, 3 H); 2.20
1
obtained. H-NMR (200 MHz, CDCl
3
(
s, 2 H); 3.71, 3.72 (2s, 3 H); 4.04, 4.11 (2s, 1 H); 4.53 ± 4.70 (m, 1 H); 7.35 ± 7.5 (m, 1 H). FAB-MS: 605 (34,
‡
‡
[2M ‡ 1] ), 303 (38, [M ‡ 1] ), 247(100), 185(31), 146(60), 86(71), 67.1(61).
t
Ac-Leu-Ama(O Bu)-Leu-OMe (3). According to GP 2, with Ac-Leu-OH (6.58 g, 38 mmol), 23 (10.9 g,
3
6 mmol), NMM (4.18 ml, 38 mmol), and isobutyl chloroformate (4.96 ml, 38 mmol) in THF (170 ml). After
workup, the combined org. layers were evaporated without further drying. The residue was stirred for 30 min in
0 ml of hot AcOEt. After cooling to r.t., the white precipitate was collected by filtration and then dried for 4 h
5
under h.v.: 8.80 g (50%) of 3. The filtrate was then cooled to � 208 (ice-NaCl bath), and additional 5.3 g (29%)
of 3 could be isolated. The first fraction contained only one epimer, whereas the second fraction was a 1 : 1
r:t:
). 1H-NMR (300 MHz,
mixture of the two possible epimers. Major isomer: [a]
CDCl
5
(
D
ˆ� 42.6 (c ˆ 1.0, CHCl
3
3
): 0.92 ± 0.94 (m, 12 H); 1.53 (s, 9 H); 1.48 ± 1.7 (m, 6 H); 2.02 (s, 3 H); 3.72 (s, 3 H); 4.56 ± 4.66 (m, 2 H);
.01 ± 5.03 (m, 1 H); 6.21 (br. s, 1 H); 7.01 (br. s, 1 H); 7.29 (br. s, 1 H). 13C-NMR (75 MHz, CDCl
): 21.94
Me); 22.07 (Me); 22.76 (Me); 22.96 (Me); 23.14 (Me); 24.82 (CH); 27.80 (Me); 41.52 (CH ); 51.24 (CH);
1.46 (CH); 52.32 (Me); 57.29 (CH); 84.29 (C); 164.50 (C); 165.45 (C); 170.04 (C); 172.18 (C); 172.60 (C).
FAB-MS: 915 (10, [2M ‡ 1] ), 457 (33, [M ‡ 1] ), 401(54), 306(10), 246(27), 202(18), 155(55), 153(52),
27(68), 85(100).
.4. Synthesis of Boc-Leu-Aca-Leu-OMe (4). N-Boc-Aminoacetonitrile (14). To a soln. of aminoacetonitrile
hydrochloride (4.58 g, 50 mmol) in dioxane (100 ml), H O (50 ml), and 1n NaOH soln. (50 ml), Boc O (12.0 g,
5 mmol) was added at 08. After 24 h stirring at r.t., the mixture was diluted with CH Cl . The aq. layer was
3
2
5
‡
‡
1
4
2
2
5
2
2
extracted twice with 100 ml of CH
dried (MgSO
.06 (d, J ˆ 5.7, 2 H); 5.11 (s, 1 H). C-NMR (50 MHz, CDCl
C); 155.08 (C).
Boc-Aca-OH (15). According to GP 1, with DIPA (3.63 ml, 25.6 mmol), TMEDA (3.84 ml, 25.6 mmol),
2
Cl
2
. The combined org. layers were washed twice with aq. sat. NaCl soln.,
1
4
), and evaporated: 7.50 g (96%) of 14. Colorless oil. H-NMR (200 MHz, CDCl
3
): 1.45 (s, 9 H);
1
3
4
(
3
): 28.06 (Me); 28.94 (CH
2
); 81.15 (C); 116.61
and BuLi (18.2 ml, 25.6 mmol) in THF (20 ml), and Boc-aminoacetonitrile (2.0 g, 12 mmol) in THF (10 ml).
1
After workup, 2.32 g (90%) of 15 were obtained. Colorless oil. Used without purification. H-NMR (200 MHz,
3
CDCl ): 1.45 (s, 9 H); 5.00 (s, 0.5 H); 5.25 (d, 0.5 H); 5.80 (d, 0.5 H); 7.10 (s, 0.5 H); 10.1 (br. s, 1 H).
Boc-Aca-Leu-OMe (24). According to GP 3, with 15 (2.30 g, 11.0 mmol), TsOH ´ H-Leu-OMe (3.80 g,
12 mmol), HOBt (1.62 g, 12 mmol), NMM (1.32 ml, 12 mmol), and DCC (2.72 g, 13 mmol) in THF (20 ml; 16 h
at r.t.). After workup and purification with FC (hexane/AcOEt 3 : 1), 1.92 g (51%) of 24 were obtained.
1
3
H-NMR (300 MHz, CDCl ; 2 epimers): 0.92 ± 0.94 (m, 6 H); 1.33 (s, 9 H); 1.58 ± 1.88 (m, 3 H); 3.75 (s, 3 H);
13
4
(
5
[
.58 ± 4.65 (m, 1 H); 5.24 (br. s, 1 H); 5.79, 5.91 (2 br. s, 1 H); 7.00, 7.16 (2d, J ˆ 7.8, 8.1, 1 H). C-NMR
75 MHz, CDCl
3
): 21.57 (Me); 22.59 (Me); 24.64 (CH); 28.01 (Me); 40.92 (CH
2
); 45.76 (CH); 51.60 (CH);
‡
2.58 (CH
2
); 82.07 (C); 115.24 (C); 154.58 (C); 162.40 (C); 172.87 (C). FAB-MS: 655 (12, [2M ‡ 1] ), 328 (21,
‡
M ‡ 1] ), 272(100), 240(6), 212(49).
2 2
H-Aca-Leu-OMe ´ HCl (25 ´ HCl). To a soln. of 24 (0.240 g, 0.73 mmol) in Et O (10 ml), a sat. HCl/Et O
soln. (30 ml) was added, and the mixture was stirred at r.t. for 5 h. After evaporation, 0.19 g (98%) of 25 ´ HCl
1
were obtained. White foam. H-NMR (300 MHz, CD
3
(
3
OD; 2 epimers): 0.89 ± 0.99 (m, 6 H); 1.64 ± 1.76 (m, 3 H);
OD; 2 epimers): 21.54
); 52.71, 52.89 (CH); 52.90, 53.06 (CH); 56.66,
.732, 3.738 (2s, 3 H); 4.50 ± 4.59 (m, 1 H); 4.65, 4.68 (2s, 1 H). 13C-NMR (75 MHz, CD
Me); 23.16, 23.22 (Me); 25.92, 25.98 (CH); 40.93, 41.38 (CH
6.64 (CH); 111.37 (C); 165.33 (C); 174.09, 174.57 (C).
3
2
5
2
Boc-Leu-Aca-Leu-OMe (4). According to GP 2, with Boc-Leu-OH ´ H O (0.180 g, 0.72 mmol), 25 ´ HCl
(
(
0.190 g, 0.72 mmol), NMM (0.16 ml, 1.44 mmol), and isobutyl chloroformate (0.10 ml, 0.72 mmol) in THF
5 ml) and DMF (5 ml). FC (hexane/AcOEt 1 : 1): 0.20 g (63%) of 4. Light-yellow foam. H-NMR (400 MHz,
1
3
CDCl ; 2 epimers): 0.91 ± 0.96 (m, 12 H); 1.45 (s, 9 H); 1.50 ± 1.74 (m, 6 H); 3.75, 3.78 (2s, 3 H); 4.21, 4.33

1868
Helvetica Chimica Acta ± Vol. 81 (1998)
(
7
(
2 br. m, 1 H); 4.56 ± 4.64 (m, 1 H); 5.12, 5.31 (2 br. s, 1 H); 5.46, 5.52 (2d, J ˆ 5.7, 7.6, 1 H); 7.73 (br. s, 1 H);
13
.80 (d, J ˆ 7.2, 1 H). C-NMR (100 MHz, CDCl
3
; 2 epimers): 21.65, 21.80 (Me); 22.69, 22.77 (Me); 22.95
); 40.90, 41.02 (CH ); 43.88
Me); 23.00 (Me); 24.71, 24.76 (CH); 24.83 (CH); 28.31 (Me); 40.71, 40.79 (CH
2
2
(
1
7
CH); 44.39 (CH); 51.51, 51.77 (CH); 52.58, 52.71 (Me); 80.82 (C); 114.72, 115.04 (C); 155.97, 155.38 (C);
‡
‡
61.85, 162.03 (C); 172.48 (C); 173.32, 173.46 (C). FAB-MS: 1322 (2, [3M ‡ 1] ), 881 (26, [2M ‡ 1] ), 781(15),
‡
25(14), 441 (29, [M ‡ 1] ), 385(61), 341(100).
t
4
.5. Synthesis of Z-Val-Leu-Ama(O Bu)-Abu-Ile-OMe (5). Boc-Abu-Ile-OH. A suspension of Boc-Abu-
2
Ile-OBn (40.63 g, 0.1 mmol) and 10% Pd/C (0.54 g) in MeOH (200 ml) was stirred for 12 h under H (balloon)
r:t:
at r.t. Filtration (Celite) and evaporation gave 31.56g (99.7%) of Boc-Abu-Ile-OH. [a]
D
ˆ‡ 33.9 (c ˆ 1.0,
1
CHCl
3
). H-NMR (300 MHz, CDCl
3
): 0.89 ± 0.94 (m, 9 H); 1.16 ± 1.26 (m, 1 H); 1.39 ± 1.53 (m, 1 H); 1.43
(
8
1
(
(
s, 9 H); 1.61 ± 1.68 (m, 1 H); 1.78 ± 1.85 (m, 1 H); 1.92 ± 1.99 (m, 1 H); 4.09 ± 4.11 (br. m, 1 H); 4.59 (dd, J ˆ 4.9,
.5, 1 H); 5.29 ± 5.30 (br. m, 1 H); 6.91 ± 7.00 (br. m, 1 H). 13C-NMR (75 MHz, CDCl
): 9.91 (Me); 11.54 (Me);
); 55.73 (CH); 56.51 (CH); 80.26 (C); 156.02
3
5.32 (Me); 24.84 (CH
2
); 25.44 (CH
2
); 27.91 (Me); 37.64 (CH
2
‡
‡
‡
C); 172.48 (C); 174.75 (C). FAB-MS: 1290 (0.3, [M ‡ 23] ), 993 (2, [3M ‡ 23] ), 655 (28, [2M ‡ 23] ), 339
‡
‡
82, [M ‡ 23] ), 317 (58, [M ‡ 1] ), 261(100), 217(64).
2
Boc-Abu-Ile-OMe. A soln. of Boc-Abu-Ile-OH (31.00 g, 97.9 mmol) in Et O (150 ml) was treated with
CH
2
N
2
, until a yellow color appeared. Excess CH
2
N
2
was destroyed by adding a few drops of AcOH. Drying
1
(
(
(
(
MgSO
4
) and evaporation gave 32.36 g (quant.) of Boc-Abu-Ile-OMe. H-NMR (300 MHz, CDCl
3
): 0.83 ± 0.93
m, 9 H); 1.05 ± 1.21 (m, 1 H); 1.40 (s, 9 H); 1.36 ± 1.45 (m, 1 H); 1.54 ± 1.70 (m, 1 H); 1.75 ± 1.92 (m, 2 H); 3.68
13
s, 3 H); 4.00 ± 4.10 (m, 1 H); 4.53 (dd, J ˆ 5.0, 8.5, 1 H); 5.18 (d, J ˆ 7.5, 1 H); 6.65 (d, J ˆ 7.5, 1 H). C-NMR
75 MHz, CDCl ): 9.87 (Me); 11.29 (Me); 15.29 (Me); 24.91 (CH ); 25.39 (CH ); 28.15 (Me); 37.68 (CH);
3
2
2
5
1
1.92 (Me); 55.62 (CH); 56.29 (CH); 79.75 (C); 155.59 (C); 171.84 (C); 172.10 (C). FAB-MS: 330 (0.4, [M ‡
‡
] ), 197(7.9), 158(11), 102(37), 86(16), 58(100).
2
HCl ´ H-Abu-Ile-OMe (26 ´ HCl). To a soln. of Boc-Abu-Ile-OMe (32.0 g, 99 mmol) in Et O (100 ml), a sat.
HCl/Et
quant.) of 26 ´ HCl were obtained. White foam. H-NMR (300 MHz, CDCl
.55 (br. m, 2 H); 1.85 ± 2.15 (br. m, 3 H); 3.67 (s, 3 H); 4.35 ± 4.55 (br. m, 2 H); 8.15 ± 8.30 (br. m, 3 H).
2
O soln. (300 ml) was added, and the mixture was stirred at r.t. for 12 h. After evaporation, 25.73 g
1
(
3
): 0.80 ± 1.00 (br. m, 9 H); 1.20 ±
1
1
3
C-NMR (75 MHz, CDCl
3
): 8.94 (Me); 11.49 (Me); 15.44 (Me); 24.95 (CH
2
); 25.28 (CH
2
); 36.65 (CH); 51.91
‡
‡
(
(
Me); 54.28 (CH); 57.72 (CH); 169.27 (C); 171.73 (C). FAB-MS: 691 (1, [3M ‡ 1] ), 461 (23, [2M ‡ 1] ), 231
‡
100, [M ‡ 1] ), 154(26), 146(24), 137(20), 136(20).
t
Z-Ama(O Bu)-Abu-Ile-OMe (27). According to GP 3, with 12 (15.70 g, 50 mmol), 26 ´ HCl (14.67 g,
5
0 mmol), HOBt (7.43 g, 55 mmol), NMM (12.12 ml, 100 mmol), and DCC (11.35 g, 65 mmol) in THF
1
(
(
1
(
(
2
500 ml); 48 h at r.t. FC (AcOEt/hexane 1 : 2): 25.34 g (69%) of 27. White foam. M.p. 125.4 ± 127.6. H-NMR
300 MHz, CDCl
.60 ± 1.78 (m, 1 H); 1.80 ± 2.00 (m, 2 H); 3.70 (s, 3 H); 4.35 ± 4.45 (m, 1 H); 4.52 ± 4.60 (m, 1 H); 4.78 ± 4.88
m, 1 H); 5.13 (s, 2 H); 6.00 ± 6.10 (m, 1 H); 6.40 ± 6.55 (m, 1 H); 6.92, 7.02 (2d, J ˆ 7.5, 7.5, 1 H); 7.28 ± 7.40
3
; 2 epimers): 0.85 ± 0.95 (m, 9 H); 1.17 ± 1.20 (m, 1 H); 1.30 ± 1.50 (m, 1 H); 1.46 (s, 9 H);
1
3
m, 5 H). C-NMR (75 MHz, CDCl
6.03, 26.27 (CH ); 27.72, 27.85 (Me); 37.87 (CH); 52.13 (Me); 54.58 (CH); 56.47, 56.54 (CH); 58.67, 58.81
CH); 67.18 (CH ); 83.90, 84.17 (C); 128.07 (CH); 128.46 (CH); 136.15 (C); 155.82, 155,88 (C); 164.7 (C);
3 2
; 2 epimers): 9.57 (Me); 11.57 (Me); 15.41 (Me); 25.02, 25.14 (CH );
2
(
2
‡
‡
1
4
65.75, 166.04 (C); 170.52, 170.55 (C); 172.14 (C). FAB-MS: 1043 (19, [2M ‡ 1] ), 522 (66, [M ‡ 1] ),
66(100), 146(26).
t
H-Ama(O Bu)-Abu-Ile-OMe (28). A suspension of 27 (24.66 g, 47.3 mmol), and 10% Pd/C (0.5 g) in
MeOH (200 ml) was stirred under H
2
(balloon) at r.t. for 18 h. Filtration (Celite) and evaporation yielded 18.32 g
; 2 epimers): 0.85 ± 0.93 (m, 9 H); 1.10 ± 1.25 (m, 1 H); 1.30 ± 1.5
1
(
(
(
(
quant.) of 28. H-NMR (300 MHz, CDCl
m, 1 H); 1.47, 1.48 (2s, 9 H); 1.62 ± 1.72 (m, 1 H); 1.80 ± 1.91 (m, 2 H); 2.01 (br. m, 2 H); 3.71 (s, 3 H); 4.01, 4.02
3
13
2s, 1 H); 4.38 ± 4.43 (m, 1 H); 4.52 ± 4.56 (m, 1 H); 6.60 ± 6.67 (m, 1 H); 7.44, 7.53 (2d, J ˆ 8, 8, 1 H). C-NMR
75 MHz, CDCl
3
: 2 epimers): 9.58 (Me); 11.41 (Me); 15.33 (Me); 24.96 (CH
2
); 25.62; 25.95 (CH
2
); 27.70 (Me);
3
7.49 (CH); 51.90, 52.09 (CH
2
); 54.06, 54.28 (CH); 56.39 (CH); 59.13 (CH); 82.81, 82.96 (C); 168.33, 168.40
‡
‡
(
1
C); 169.24, 169.37 (C); 170.98 (C); 172.04 (C). FAB-MS: 775 (100, [2M ‡ 1] ), 756(88), 388 (23, [M ‡ 1] ),
46(82).
Z-Leu-Ama(O Bu)-Abu-Ile-OMe (29). According to GP 2, with Z-Leu-OH (13.26 g, 50 mmol), 28
18.32 g, 47.3 mmol), NMM (11.0 ml, 100 mmol), and isobutyl chloroformate (6.53 ml, 50 mmol) in THF
t
(
(
400 ml) and DMF (20 ml). After workup and evaporation, the residue was stirred for 2 h in refluxing Et
2
O.
1
Filtration and drying of the solid gave 29.36 g (96%) of 29. White amorpous solid. M.p. > 1608 (dec.). H-NMR
(
(
300 MHz, (D
6
)DMSO; 2 epimers): 0.80 ± 0.90 (m, 15 H); 1.12 ± 1.24 (m, 1 H); 1.37, 1.37 (2s, 9 H); 1.41 ± 1.89
m, 7 H); 3.61, 3.61 (2s, 3 H); 4.11 ± 4.24 (m, 1 H); 4.33 ± 4.40 (m, 1 H); 4.97 ± 5.10 (m, 3 H); 7.28 ± 7.39

Helvetica Chimica Acta ± Vol. 81 (1998)
1869
(
m, 5 H); 7.48, 7.69 (2d, J ˆ 8.5, 8.5, 1 H); 8.10 (d, J ˆ 7.5, 0.3 H); 8.23 ± 8.34 (m, 2 H); 8.51 (d, J ˆ 8, 0.7 H).
1
3
C-NMR (75 MHz, (D
3.04 (Me); 24.12 (CH); 24.66, 24.79 (CH
Me); 52.79, 53.08 (CH); 53.47, 53.56 (CH); 56.28, 56.42 (CH); 56.81 (CH); 65.27 (CH
6
)DMSO; 2 epimers): 9.67, 9.83 (Me); 11.01, 11.10 (Me); 15.31 (Me); 21.13 (Me); 22.91,
); 25.52 (CH ); 27.31, 27.41 (Me); 36.06 (CH); 40.45 (CH ); 51.44
); 81.54, 81.76 (C);
2
(
2
2
2
2
1
1
2
27.42, 127.51 (CH); 127.63 (CH); 128.22 (CH); 136.98 (C); 155.83 (C); 164.80, 165.09 (C); 166.32, 166.48 (C);
‡
70.95, 171.27 (C); 171.69 (C); 172.30, 172.50 (C). FAB-MS: 1269 (16, [2M ‡ 1] ), 1135(9), 657 (21, [M ‡
‡
‡
3] ), 635 (100, [M ‡ 1] ), 579(60), 305(29), 231(24), 176( 22), 154(49), 146(49).
t
H-Leu-Ama(O Bu)-Abu-Ile-OMe (30). A suspension of 29 (29.0 g, 44.8 mmol), and 10% Pd/C (1.5 g) in
MeOH (400 ml) and DMF (100 ml) was stirred under H
evaporation, 23.06 g (quant.) of 30 were obtained. White powder. H-NMR (300 MHz, CDCl
2
(balloon) at r.t. for 12 h. After filtration (Celite) and
1
3
; 2 epimers):
0
3
.81 ± 1.00 (m, 15 H); 1.09 ± 1.28 (m, 1 H); 1.34 ± 1.48 (m, 3 H); 1.48, 1.50 (2s, 9 H); 1.62 ± 2.03 (m, 6 H); 3.42 ±
.48 (m, 1 H); 3.73 (s, 3 H); 4.40 ± 4.47 (m, 1 H); 4.54 ± 4.60 (m, 1 H); 4.99, 5.06 (2d, J ˆ 7, 7.3, 1 H); 6.64, 6.67
13
(
2d, J ˆ 6.6, 8.4, 1 H); 7.16, 7.21 (2d, J ˆ 7.9, 7.9, 1 H); 8.19, 8.26 (2d, J ˆ 7, 7.3, 1 H). C-NMR (85 MHz,
CDCl ; 2 epimers): 9.69 (Me); 11.56 (Me); 15.50 (Me); 21.36 (Me); 23.40 (Me); 24.81 (CH); 25.08, 25.20
); 25.70, 25.86 (CH ); 27.80, 27.90 (Me); 37.75 (CH); 43.81, 43.92 (CH ); 52.14 (Me); 53.41 (CH); 54.83
CH); 56.58 (CH); 57.04, 57.32 (CH); 83.87, 84.03 (C); 165.35 (C); 165.91 (C); 170.63 (C); 172.18 (C); 176.11,
3
(
(
CH
2
2
2
‡
‡
176.26 (C). FAB-MS: 1001 (89, [2M ‡ 1] ), 501 (100, [M ‡ 1] ), 445(67), 231(33), 146(81).
t
Z-Val-Leu-Ama(O Bu)-Abu-Ile-OMe (5). According to GP 2, with Z-Val-OH (12.54 g, 50 mmol), 30
(
(
23.00 g, 44.8 mmol), NMM (11.0 ml, 50 mmol), and isobutyl chloroformate (6.53 ml, 50 mmol) in THF
350 ml) and DMF (100 ml). During the washing and extraction steps, a white precipitate appeared in the org.
layers: 18.78 g (55%) of 5. The aq. layers were extracted twice with 200 ml of AcOEt. The combined org. layers
were dried (MgSO ) and evaporated. The residue was stirred in 100 ml of AcOEt for 1 h at 608. After cooling to
r.t., 9.43 g (26%) of 5 were obtained. Total yield: 28.21 g (81%) of 5. White powder. 1H-NMR (300 MHz,
)DMSO; 2 epimers): 0.80 ± 0.89 (m, 21 H); 1.11 ± 1.24 (m, 1 H); 1.35, 1.37 (2s, 9 H); 1.41 ± 1.78 (m, 7 H);
.92 ± 1.98 (m, 1 H); 3.61, 3.61 (2s, 3 H); 3.84 ± 3.89 (m, 1 H); 4.15 ± 4.22 (m, 1 H); 4.32 ± 4.53 (m, 2 H); 4.98 ±
4
(
D
6
1
5
.10 (m, 3 H); 7.28 ± 7.36 (m, 6 H); 7.97, 8.07 (2d, J ˆ 8, 8, 1 H); 8.23 ± 8.32 (m, 1.5 H); 8.50 (d, J ˆ 8, 0.5 H).
13
C-NMR (75 MHz, (D
Me); 21.21 (Me); 22.69, 23.11 (Me); 23.95 (CH); 24.66, 24.79 (CH
0.20 (CH); 36.05 (CH); 40.59, 40.68 (CH ); 50.46, 50.79 (CH); 51.46 (Me); 53.41, 53.53 (CH); 56.22, 56.42
); 81.47, 81.67 (C); 127.50 (CH); 127.63 (CH); 127.79 (CH); 128.22
CH); 137.04 (C); 155.95 (C); 164.76, 164.99 (C); 166.27, 166.41 (C); 170.91, 170.98 (C); 171.27 (C); 171.67 (C);
6
)DMSO; 2 epimers): 9.67, 9.80 (Me); 11.00, 11.10 (Me); 15.31 (Me); 18.00 (Me); 19.19
(
3
(
(
2
); 25.54 (CH ); 27.30, 27.41 (Me); 30.13,
2
2
CH); 56.81 (CH); 60.13 (CH); 65.25 (CH
2
‡
‡
‡
1
1
71.95, 172.05 (C). FAB-MS: 1490 (9, [2M ‡ 23] ), 1468 (10, [2M ‡ 1] ), 756 (100, [M ‡ 23] ), 734 (55, [M ‡
‡
] ), 678(48), 656(30), 600(21), 404(48), 347(22), 231(28), 176(28), 146(49).
4
.6. Synthesis of Boc-Val-Leu-Ama(OBn)-Abu-Ile-OMe (6). Boc-Ama(OBn)-Abu-Ile-OMe (31). Accord-
ing to GP 3, with 10 (24.68 g, 80 mmol), 26 ´ HCl (24.20 g, 81 mmol), HOBt (11.4 g, 80 mmol), NMM (17.6 ml,
1
60 mmol), and DCC (18.5 g, 90 mmol) in THF (300 ml) and DMF (60 ml). FC (hexane/AcOEt 3 : 1): 28.07 g
1
(
67%) of 31. White foam. H-NMR (300 MHz, CDCl
3
; 2 epimers): 0.73 ± 0.90 (m, 9 H); 1.05 ± 1.20 (m, 1 H);
1
5
7
2
.40 (s, 9 H); 1.33 ± 1.58 (m, 1 H); 1.60 ± 1.75 (m, 1 H); 1.80 ± 1.91 (m, 2 H); 3.70 (s, 1 H); 4.46 ± 4.57 (m, 2 H);
.00 (d, J ˆ 7, 1 H); 5.10 ± 5.26 (m, 2 H); 5.96 (d, J ˆ 8, 1 H); 6.88 ± 6.93 (m, 1 H); 7.22 ± 7.26 (m, 1 H); 7.30 ±
1
3
.35 (m, 5 H). C-NMR (75 MHz, CDCl
5.58 (CH ); 28.09 (Me); 37.57 (CH); 51.99 (Me); 54.43, 54.58 (CH); 56.42 (CH); 57.89 (CH); 67.86, 67.96
); 80.34, 80.41 (C); 128.13 (CH); 128.37 (CH); 128.43 (CH); 134.66 (C); 155.04 (C); 164.74, 164.98 (C);
3 2
; 2 epimers): 9.31, 9.43 (Me); 11.42 (Me); 15.27 (Me); 24.98 (CH );
2
(CH
2
‡
‡
1
1
67.41 (C); 170.47, 170.55 (C); 172.04 (C). FAB-MS: 1565 (2, [3M ‡ 1] ), 1043 (52, [2M ‡ 1] ), 522 (95, [M ‡
‡
] ), 466(100), 146(83).
HCl ´ H-Ama(OBn)-Abu-Ile-OMe (32 ´ HCl). To a soln. of 31 (19.70 g, 37.0 mmol) in Et
2
O (30 ml), a sat.
HCl/Et O soln. (300 ml) was added, and the mixture was stirred at r.t. for 12 h. After evaporation, 16.76 g
2
1
(
3
quant.) of 32 ´ HCl were obtained. White foam. H-NMR (300 MHz, CDCl ; 2 epimers): 0.64 ± 0.69 (m, 2 H);
0
4
.77 ± 0.88 (m, 7 H); 1.16 ± 1.29 (m, 1 H); 1.30 ± 1.45 (m, 1 H); 1.55 ± 1.95 (m, 3 H); 3.59, 3.62 (2s, 3 H); 4.36 ±
.60 (m, 2 H); 5.09 ± 5.28 (m, 2 H); 5.43, 5.55 (2 br. s, 1 H); 7.21 ± 7.37 (m, 5.5 H); 7.65 (br. d, 0.5 H); 8.60 ± 8.84
1
3
(
br. m, 4 H). C-NMR (75 MHz, CDCl
3
; 2 epimers): 9.67, 9.81 (Me); 11.25, 11.39 (Me); 15.32, 15.38 (Me);
); 36.70, 37.11 (CH); 51.99 (Me); 55.75, 55.93 (CH); 56.69, 56.99 (CH);
); 128.07 (CH); 128.32 (CH); 128.46 (CH); 134.09, 134.23 (C); 162.23, 162.45 (C); 164.43, 164.60
2
6
5.13, 25.31 (CH
9.02 (CH
2 2
); 25.50, 25.73 (CH
2
‡
‡
(
1
C); 170.91, 171.53 (C); 172.24, 172.57 (C). FAB-MS: 843 (36, [2M ‡ 1] ), 422 (100, [M ‡ 1] ), 231(32),
46(65).
Boc-Leu-Ama(OBn)-Abu-Ile-OMe (33). According to GP 2, with Boc-Leu-OH ´ H
2 (16.71 g, 37 mmol), NMM (8.8 ml, 80 mmol), and isobutyl chloroformate (5.3 ml, 40 mmol) in THF
2
O (9.97 g, 40 mmol),
3

1870
Helvetica Chimica Acta ± Vol. 81 (1998)
(
300 ml). After workup, 24.42 g (95%) of 33 were obtained. For anal. purposes, 33 was purified by FC (hexane/
1
AcOEt 2 : 1). H-NMR (300 MHz, CDCl
3
; 2 epimers): 0.75 ± 0.80 (m, 2 H); 0.84 ± 0.92 (m, 13 H); 1.09 ± 1.20
(
(
(
9
(
(
1
1
1
m, 1 H); 1.30 ± 1.55 (m, 2 H); 1.42 (s, 9 H); 1.55 ± 1.75 (m, 3 H); 1.75 ± 1.95 (m, 2 H); 3.72 (s, 3 H); 4.15 ± 4.30
m, 1 H); 4.35 ± 4.50 (m, 1 H); 4.55 ± 4.60 (m, 1 H); 5.10 ± 5.28 (m, 3 H); 6.78, 6.83 (2d, J ˆ 7.5, 7.5, 1 H); 7.10
13
d, J ˆ 7.5, 0.5 H); 7.28 ± 7.36 (m, 5.5 H); 7.45 ± 7.55 (br. m, 1 H). C-NMR (75 MHz, CDCl
.89 (Me); 11.52 (Me); 15.40 (Me); 21.69, 21.84 (Me); 22.58 (Me); 24.66, 24.95 (CH); 25.12, 25.28 (CH
CH ); 28.26 (Me); 37.66, 37.80 (CH); 41.25, 41.36 (CH ); 52.10, 52.18 (Me); 52.91, 53.39 (CH); 55.03, 55.25
CH); 56.42, 56.53 (CH); 56.74, 57.04 (CH); 68.14, 68.29 (CH ); 80.01, 80.37 (C); 128.31 (CH); 128.54 (CH);
28.63 (CH); 134.66 (C); 155.72 (C); 164.41, 164.75 (C); 166.67, 166.80 (C); 170.62 (C); 172.14, 172.59 (C);
3
; 2 epimers): 9.67,
2
); 25.45
2
2
2
‡
‡
72.88, 173.02 (C). FAB-MS: 1269 (4, [2M ‡ 1] ), 635 (22, [M ‡ 1] ), 534(52), 433(26), 348(23), 230(37),
45(79), 90(100).
HCl ´ H-Leu-Ama(OBn)-Abu-Ile-OMe (34 ´ HCl). A soln. of 33 (24.0 g, 37 mmol) in sat. HCl/Et
2
O soln.
(
300 ml) was stirred at r.t. for 12 h and then evaporated to yield 21.11 g (quant.) of 34 ´ HCl. Yellow foam.
1
H-NMR (300 MHz, CDCl
3
; 2 epimers): 0.71 ± 0.96 (m, 15 H); 1.12 ± 1.27 (m, 1 H); 1.33 ± 1.43 (m, 1 H); 1.60 ±
1
.84 (m, 7 H); 3.69 (s, 9 H); 4.34 ± 4.70 (m, 4 H); 5.03 ± 5.23 (m, 2 H); 5.65 ± 5.68 (br. m, 1 H); 7.24 ± 7.37
1
3
(
(
(
(
[
m, 5 H); 8.19 ± 8.47 (br. m, 4 H). C-NMR (85 MHz, CDCl
Me); 22.31 (Me); 22.49 (CH); 24.27 (CH); 25.22, 25.38 (CH
CH ); 52.08, 52,57 (Me); 55.16 (CH); 56.68 (CH); 56.90, 56.98 (CH); 68.14, 68.36 (CH
CH); 134.69 (C); 164.73 (C); 166.81 (C); 169.87, 170.07 (C); 171.23, 171.85 (C); 172.50 (C). FAB-MS: 1604 (2,
3M ‡ 1] ), 1069 (29, [2M ‡ 1] ), 535 (100, [M ‡ 1] ), 390(7), 305(9), 231(15), 176(22), 146(26), 90(89),
6(88).
Boc-Val-Leu-Ama(OBn)-Abu-Ile-OMe (6). According to GP 2, with Boc-Val-OH (8.69 g, 40 mmol), 34 ´
3
; 2 epimers): 9.65, 9.94 (Me); 11.57 (Me); 15.51
); 25.73, 26.13 (CH ); 37.20, 37.45 (CH); 40.35
); 128.38 (CH); 128.63
2
2
2
2
‡
‡
‡
8
HCl (21.11 g, 37 mmol), NMM (8.8 ml, 80 mmol), and isobutyl chloroformate (5.3 ml, 40 mmol) in THF
1
(
300 ml). FC (hexane/AcOEt 2 : 1): 23.95 g (85%) of 6. Yellowish foam. H-NMR (300 MHz, (D
6
)DMSO; 2
epimers): 0.73 ± 0.88 (m, 21 H); 1.14 ± 1.19 (m, 1 H); 1.36 (s, 9 H); 1.40 ± 1.82 (m, 7 H); 1.84 ± 1.97 (m, 1 H); 3.60
(
(
(
8
1
2
5
1
1
s, 3 H); 3.70 ± 3.80 (m, 1 H); 4.15 ± 4.22 (m, 1 H); 4.32 ± 4.40 (m, 1 H); 4.40 ± 4.58 (m, 1 H); 5.07 ± 5.19
m, 2 H); 5.25, 5.35 (2d, J ˆ 7.6, 8.0, 1 H); 6.70, 6.74 (2d, J ˆ 9.2, 9.3, 1 H); 7.28 ± 7.38 (m, 5 H); 7.85, 7.96
2d, J ˆ 8.3, 8.4, 1 H); 8.16, 8.22 (2d, J ˆ 7.7, 7.7, 1 H); 8.33, 8.52 (2d, J ˆ 7.7, 8.0, 1 H); 8.47, 8.62 (2d, J ˆ 8.0,
1
3
3
.3, 1 H). C-NMR (75 MHz, CDCl ; 2 epimers): 9.26, 9.66 (Me); 11.42, 11.53 (Me); 15.16, 15.21 (Me); 18.04,
8.30 (Me); 19.12, 19.27 (Me); 22.12, 22.33 (Me); 22.77, 23.00 (Me); 24.45 (CH); 24.81, 25.03 (CH
6.57 (CH ); 28.30 (Me); 31.31, 31.82 (CH); 37.59, 38.04 (CH); 42.30 (CH ); 51.08 (CH); 52.01, 52.11 (Me);
4.01, 54.44 (CH); 56.02, 56.30 (CH); 56.35, 56.58 (CH); 59.5, 59.57 (CH); 67.06, 67.79 (CH ); 78.90, 79.09 (C);
2
); 26.31,
2
2
2
27.29, 127.88 (CH); 128.37, 128.47 (CH); 134.81, 134.09 (C); 155.78, 155.96 (C); 164.16, 165.17 (C); 166.50,
66.85 (C); 170.76, 171.12 (C); 171.66, 171.79 (C); 172.47, 172.63 (C); 172.76, 172.93 (C). FAB-MS: 1468 (15,
‡
‡
[
2M ‡ 1] ), 1368(2), 734 (31, [M ‡ 1] ), 533(17), 422(15), 231(15), 146(28), 116(16).
.7. Synthesis of Boc-Val-Leu-Ama(OAll)-Abu-Ile-OMe (7). Boc-Gly-OAll. To a cold (08) soln. of Boc-Gly-
OH (8.75 g, 50 mmol) and allylic alcohol (3.8 ml, 55 mmol) in CH Cl (100 ml), DMAP (0.610 g, 5 mmol) and
DCC (11.34 g, 55 mmol) were added. A white precipitate appeared. After 3 h, the solid was filtered off. The org.
soln. was washed with 50 ml of aq. sat. NaHCO and sat. NaCl soln. The org. phase was dried (MgSO ) and
O 3 :1), Boc-Gly-OAll (10.34 g, 96%) was obtained.
4
2
2
3
4
evaporated. After purification with FC (pentane/Et
2
1
Colorless oil. H-NMR (200 MHz, CDCl
(
(
3
): 1.37 (s, 9 H); 3.74 (d, J ˆ 5.8, 2 H); 4.46 ± 4.50 (m, 2 H); 5.06 ± 5.26
m, 2 H); 5.45 (br. s, 1 H); 5.72 ± 5.92 (m, 1 H). 13C-NMR (50 MHz, CDCl
CH ); 81.73 (C); 117.34 (CH ); 132.58 (CH); 156.07 (C); 169.03 (C).
Boc-Ama(OAll)-OH (11). According to GP 1, with DIPA (2.9 ml, 20 mmol), TMEDA (3.06 ml, 20 mmol),
): 27.76 (Me); 43.12 (CH ); 65.47
3
2
2
2
and BuLi (14.61 ml, 20 mmol) in THF (60 ml), and Boc-Gly-OAll (2.0 g, 9.29 mmol) in THF (20 ml). After
workup, 2.26 g (quant.) of 11 were obtained. Colorless oil. Used without further purification. 1H-NMR
(
(
3
200 MHz, CDCl ): 1.44 (s, 9 H); 4.60 ± 4.85 (m, 2 H); 5.05 (m, 0.5 H); 5.23 ± 5.45 (m, 2 H); 5.60 ± 5.70
br. d, 0.5 H); 5.90 ± 6.05 (m, 1 H); 7.50 (br. s, 1 H); 10.25 (br. s, 1 H).
Boc-Ama(OAll)-Abu-Ile-OMe (35). According to GP 4, with 11 (0.58 g, 2.3 mmol), 26 ´ HCl (0.508 g,
2
.3 mmol), NMM (2.04 ml, 4.6 mmol), HOBt (0.76 g, 5 mmol), and EDC (0.955 g, 5 mmol) in THF (20 ml).
1
FC (hexane/AcOEt 2 : 1): 0.688 g (65%) of 35. White foam. R
CDCl
.75 (m, 1 H); 1.85 ± 1.96 (m, 2 H); 3.73, 3.74 (2s, 3 H); 4.37 ± 4.44 (m, 1 H); 4.56, 4.57 (2dd, J
.6, 1 H); 4.64 ± 4.74 (m, 2 H); 4.92 (br. m 1 H); 5.24 ± 5.28 (m, 1 H); 5.32 ± 5.38 (m, 1 H); 5.80 ± 5.82
f
(AcOEt/hexane 1 : 1) 0.58. H-NMR (400 MHz,
3
: 2 epimers): 0.87 ± 0.94 (m, 9 H); 1.08 ± 1.21 (m, 1 H); 1.35 ± 1.44 (m, 1 H); 1.443, 1.449 (2s, 9 H); 1.64 ±
ˆ 4.9, 8.5, J ˆ 4.9,
1
8
1
2
13
(
br. m, 1 H); 5.85 ± 5.96 (m, 1 H); 6.50 ± 6.52 (br. m, 1 H); 7.00 ± 7.03 (br. m, 1 H). C-NMR (100 MHz,
CDCl : 2 epimers): 9.46, 9.56 (Me); 11.50 (Me); 15.40 (Me); 25.04, 15.10 (CH ); 25.53 (Me); 28.19 (Me);
3
2

Helvetica Chimica Acta ± Vol. 81 (1998)
1871
37.73 (CH); 52.10 (Me); 54.70, 54.80 (CH); 56.48, 56.54 (CH); 57.93 (CH); 66.90, 66.96 (CH
2
); 80.67 (C);
1
2
19.26, 119.51 (CH ); 130.92, 131.01 (CH); 155.15 (C); 164.87, 165.07 (C); 167.22 (C); 170.38, 170.44 (C); 172.03
‡
‡
‡
(C). FAB-MS: 1414 (4, [3M ‡ 1] ), 943 (100, [2M ‡ 1] ), 472 (50, [M ‡ 1] ), 416(32).
HCl ´ H-Ama(OAll)-Abu-Ile-OMe (36 ´ HCl). In sat. HCl/Et O soln. (30 ml), 35 (0.650 g, 1.3 mmol) was
2
disolved, and the mixture was stirred at r.t. for 4 h. After evaporation, 0.58 g (quant.) of 36 ´ HCl were obtained.
1
White foam. H-NMR (300 MHz, CD
3
OD; 2 epimers): 0.87 ± 1.03 (m, 9 H); 1.14 ± 1.40 (m, 2 H); 1.40 ± 1.60
(
5
CD
(
m, 1 H); 1.63 ± 1.95 (m, 3 H); 3.71 (s, 3 H); 4.34 ± 4.51 (m, 2 H); 4.70 ± 4.95 (m, 3 H); 5.24 ± 5.44 (m, 2 H);
13
.88 ± 6.08 (m, 1 H); 8.28, 8.50 (2d, J ˆ 8.7, 7.9, 1 H); 8.64, 8.78 (2d, J ˆ 7.9, 7.4, 1 H). C-NMR (300 MHz,
OD; 2 epimers): 10.35, 10.61 (Me); 11.79 (Me); 16.06 (Me); 26.43 (CH ); 26.82, 26.89 (CH ); 38.39, 38.42
CH); 52.58 (Me); 56.43, 56.57 (CH); 58.42 (CH); 58.55 (CH); 68.96, 69.08 (CH ); 120.17, 120.46 (CH );
3
2
2
2
2
1
1
32.48, 132.59 (CH); 163.57, 163.86 (C); 165.90 (C); 173.51, 173.75 (C); 174.30 (C). FAB-MS: 745 (26, [2M ‡
‡
‡
] ), 373 (100, [M ‡ 1] ), 199(13).
2
Boc-Leu-Ama(OAll)-Abu-Ile-OMe (37). According to GP 4, with Boc-Leu-OH ´ H O (0.947 g, 3.8 mmol),
3
3
6 ´ HCl (1.50 g, 3.67 mmol), HOBt (0.518 g, 3.87 mmol), NMM (0.83 ml, 7.6 mmol), and EDC (0.747 g,
.87 mmol) in THF (30 ml). FC (hexane/AcOEt 2 : 1): 1.37 g (66%) of 37. White foam. H-NMR (400 MHz,
1
CD
(
(
3
OD; 2 epimers): 0.87 ± 0.98 (m, 15 H); 1.20 ± 1.33 (m, 1 H); 1.44 (s, 9 H); 1.44 ± 1.63 (m, 3 H); 1.65 ± 1.74
m, 2 H); 1.83 ± 1.94 (m, 2 H); 3.696, 3.698 (2s, 3 H); 4.15 ± 4.18 (br. m, 1 H); 4.31 ± 4.38 (m, 2 H); 4.62 ± 4.72
m, 2 H); 5.19 ± 5.24 (m, 2 H); 5.30 ± 5.36 (m, 1 H); 5.87 ± 5.97 (m, 1 H). 13C-NMR (100 MHz, CD
OD; 2
3
epimers): 10.50, 10.64 (Me); 11.73, 11.76 (Me); 14.45 (Me); 16.03, 16.05 (Me); 21.86, 21.94 (Me); 23.48 (Me);
2
4
1
1
5
3.71 (CH
1.95 (CH
18.94, 119.14 (CH
2
); 25.93 (CH); 26.34 (CH
); 52.42 (Me); 54.45, 54.60 (CH); 56.23, 56.38 (CH); 58.25 (CH); 58.41 (CH); 80.74, 80.81 (C);
); 12.82, 132.89 (CH); 157.94 (C); 167.02, 167.54 (C); 167.96, 168.18 (C); 173.37, 173.45 (C);
2 2 2
); 26.43, 26.46 (CH ); 28.75 (Me); 32.76 (CH ); 38.16, 38.35 (CH); 41.81,
2
2
‡
‡
‡
73.53, 173.92 (C); 175.61, 175.67 (C). FAB-MS: 1169 (8, [2M ‡ 1] ), 607 (17, [M ‡ 23] ), 585 (75, [M ‡ 1] ),
29(24), 485(100), 384(34), 372(16), 299(46), 231(24), 199(23), 146(56).
2
HCl ´ H-Leu-Ama(OAll)-Abu-Ile-OMe (38 ´ HCl). In sat. HCl/Et O soln. (30 ml), 37 (1.351 g, 2.3 mmol)
was dissolved, and the mixture was stirred at r.t. for 10 h. After evaporation, 1.166 g (quant.) of 38 ´ HCl were
1
obtained. White foam. H-NMR (400 MHz, CD
3
OD; 2 epimers): 0.89 ± 1.03 (m, 15 H); 1.21 ± 1.28 (m, 1 H);
1
4
8
2
3
5
1
.44 ± 1.51 (m, 1 H); 1.65 ± 1.82 (m, 4 H); 1.84 ± 1.91 (m, 1 H); 3.70, 3.70 (2s, 3 H); 4.04 ± 4.10 (m, 1 H); 4.33 ±
.40 (m, 2 H); 4.63 ± 4.74 (m, 2 H); 5.20 ± 5.38 (m, 3 H); 5.88 ± 5.98 (m, 1 H); 8.17 (d, J ˆ 8.2, 1 H); 8.27 (d, J ˆ
1
3
.0, 1 H). C-NMR (100 MHz, CD
3
OD; 2 epimers): 10.41, 10.61 (Me); 11.70, 11.76 (Me); 16.00, 16.03 (Me);
); 26.61, 26.67 (CH ); 38.27, 38.30 (CH);
); 52.44, 52.48 (Me); 52.82 (CH); 56.16, 56.20 (CH); 56.37, 56.41 (CH);
); 119.09, 119.33 (CH ); 132.77, 132.85 (CH); 166.85, 167.05 (C); 167.71,
2.19, 22.25 (Me); 23.06, 23.12 (Me); 25.40 (CH); 26.37, 26.44 (CH
8.35, 38.37 (CH); 41.62, 41.71 (CH
8.28, 58.37 (CH); 67.80, 67.93 (CH
2
2
2
2
2
68.09 (C); 170.84, 170.86 (C); 173.37, 173.39 (C); 173.59, 173.61 (C); 173.96, 174.05 (C). FAB-MS: 970 (54,
‡
‡
[2M ‡ 1] ), 485 (100, [M ‡ 1] ), 372(7), 255(11), 199(19).
Boc-Val-Leu-Ama(OAll)-Abu-Ile-OMe (7). According to GP 4, with Boc-Val-OH (0.543 g, 2.5 mmol),
3
2
(
8 ´ HCl (1.14 g, 2.26 mmol), NMM (0.6 ml, 5.5 mmol), HOBt (0.421 g, 2.75 mmol), and EDC (0.527 g,
.75 mmol) in THF (30 ml). FC (hexane/AcOEt 3 : 2): 1.49 g (97%) of 7. White foam. H-NMR (400MHz,
D )DMSO; 2 epimers): 0.78 ± 0.87 (m, 21 H); 1.09 ± 1.28 (m, 1 H); 1.37 (s, 9 H); 1.37 ± 1.51 (m, 4 H); 1.53 ± 1.72
6
1
(
(
(
(
(
(
4
m, 2 H); 1.74 ± 1.80 (m, 1 H); 1.88 ± 1.98 (m, 1 H); 3.614, 3.616 (2s, 3 H); 3.74 ± 3.78 (br. m, 1 H); 4.15 ± 4.22
m, 1 H); 4.32 ± 4.44 (m, 1 H); 4.46 ± 4.62 (m, 4 H); 5.14 ± 5.21 (m, 1 H); 5.26 ± 5.33 (m, 2 H); 5.79 ± 5.89
m, 1 H); 6.68, 6.71 (2d, J ˆ 9.3, 9.4, 1 H); 7,85, 7.94 (2d, J ˆ 8.1, 8.2, 1 H); 8.12, 8.20 (2d, J ˆ 7.9, 7.7, 1 H); 8.31
13
d, J ˆ 7.7, 0.5 H); 8.41 ± 8.44 (m, 1 H); 8.59 (d, J ˆ 8.3, 1 H). C-NMR (D
6
)DMSO; 2 epimers): 9.62, 9.73
Me); 11.04, 11.12 (Me); 15.28, 15.31 (Me); 18.12, 19.18 (Me); 21.22, 21.29 (Me); 21.96, 22.29 (Me); 22.98, 23.13
Me); 23.84 (CH); 24.67, 24.79 (CH ); 25.61, 25.48 (CH ); 28.05 (Me); 30.00, 30.10 (CH); 36.04, 36.09 (CH);
0.76 (CH ); 50.32, 50.61 (CH); 51.46, 51.49 (Me); 53.50 (CH); 56.02, 56.24 (CH); 56.40 (CH); 59.64, 59.72
CH); 65.23 (CH ); 77.87 (C); 117.33, 117.47 (CH ); 131.81 (CH); 155.25 (C); 164.58, 164.63 (C); 166.98, 167.17
C); 170.84, 171.09 (CH); 171.17, 171.23 (C); 171.64 (C); 171.71 (C); 172.21, 172.31 (C). FAB-MS: 1367 (11,
2
2
2
(
(
2
2
‡
‡
[2M ‡ 1] ), 684 (39, [M ‡ 1] ), 584(100), 539(10), 483(26), 398(37), 372(38), 354(20).
4
.8. Synthesis of Boc-Val-Ala-Leu-Ama(OMe)-Val-Ala-Leu-OMe (8). Boc-Ala-Leu-OBn. According to
GP 2, with Boc-Ala-OH (5.29 g, 28 mmol), TsOH ´ H-Leu-OBn (11.02 g, 28 mmol), NMM (6.17 ml, 56 mmol),
and isobutyl chloroformate (3.66 ml, 28 mmol) in THF (60 ml), and DMF (20 ml). After workup, 11.03 g
r:t:
1
(
quant.) of Boc-Ala-Leu-OBn were obtained. Colorless oil. [a]
D
ˆ� 46.6 (c ˆ 1.05, CHCl
3
). H-NMR (300 MHz,
CDCl
4
(
3
): 0.88 (d, J ˆ 6.2, 6 H); 1.30 (d, J ˆ 7, 3 H); 1.41 (s, 9 H); 1.51 ± 1.66 (m, 3 H); 4.18 ± 4.25 (m, 1 H); 4.60 ±
.66 (m, 1 H); 5.19, 5.15 (2AB, JAB ˆ 12.0, 2 H); 5.25 (br. d, J ˆ 6.5, 1 H); 6.82 (br. d, J ˆ 6.4, 1 H); 7.30 ± 7.36
13
3
m, 5 H). C-NMR (75 MHz, CDCl ): 18.06 (Me); 21.64 (Me); 22.67 (CH); 24.56 (Me); 28.15 (Me); 41.07

1872
Helvetica Chimica Acta ± Vol. 81 (1998)
(
CH
2
); 50.65 (CH); 66.82 (CH
2
); 70.83 (C); 128.02 (CH); 128.18 (CH); 128.40 (CH); 135.25 (C); 155.35 (C);
‡
‡
1
72.45 (C). FAB-MS: 785 (9, [2M ‡ 1] ), 393 (50, [M ‡ 1] ), 337(87), 293(43), 229(13), 201(10), 91(100).
HCl ´ H-Ala-Leu-OBn. To a soln. of Boc-Ala-Leu-OBn (11.03 g, 28 mmol) in Et O (20 ml), sat. HCl/Et
soln. (150 ml) was added, and the mixture was stirred at r.t. for 12 h. After evaporation, 13 g (quant.) of HCl ´ H-
Ala-Leu-OBn were obtained. Colorless oil. 1H-NMR (300 MHz, CDCl
): 0.75 ± 1.00 (br. m, 6 H); 1.45 ± 1.80
br. m, 6 H); 4.30 ± 4.55 (br. m, 2 H); 5.00 ± 5.20 (br. m, 2 H); 7.20 ± 7.35 (br. m, 5 H); 8.00 ± 8.35 (br. m, 4 H).
2
2
O
3
(
13
C-NMR (75 MHz, CDCl
3 2
): 17.85 (Me); 21.88 (Me); 22.67 (Me); 24.68 (CH); 39.96 (CH ); 49.72 (CH); 51.94
(
CH); 67.09 (CH ); 128.23 (CH); 128.52 (CH); 135.30 (C); 170.10 (C); 172.28 (C).
2
Boc-Val-Ala-Leu-OBn. According to GP 2, with Boc-Val-OH (6.08 g, 28 mmol), HCl ´ H-Ala-Leu-OBn
(
9.13 g, 28 mmol) NMM (6.17 ml, 56 mmol), and isobutyl chloroformate (3.66 ml, 28 mmol) in THF (80 ml).
r:t:
FC (hexane/AcOEt 2 : 1): 11.11 g (87%) of Boc-Val-Ala-Leu-OBn. White solid. M.p. 136.9 ± 138.08. [a]
D
ˆ
1
�
54.7 (c ˆ 1.05, CHCl
3
). H-NMR (300 MHz, CDCl
3
): 0.88 ± 0.95 (m, 12 H); 1.35 (d, J ˆ 6.5, 3 H); 1.44
(
(
(
4
s, 9 H); 1.50 ± 1.65 (m, 3 H); 2.05 ± 2.17 (m, 1 H); 3.90 ± 3.98 (m, 1 H); 4.50 ± 4.65 (m, 2 H); 5.10 ± 5.21
13
m, 3 H); 6.70 (d, J ˆ 7.3, 1 H); 6.79 (d, J ˆ 7.0, 1 H); 7.30 ± 7.40 (m, 5 H). C-NMR (75 MHz, CDCl
3
): 17.66
Me); 18.29 (Me); 19.15 (Me); 21.71 (Me); 22.68 (Me); 24.63 (CH); 28.24 (Me); 31.03 (CH); 41.00 (CH );
8.59 (CH); 50.83 (CH); 59.62 (CH); 66.90 (CH ); 79.71 (C); 128.13 (CH); 128.25 (CH); 128.45 (CH); 135.34
2
2
‡
‡
(
(
C); 155.82 (C); 171.51 (C); 171.94 (C); 172.45 (C). FAB-MS: 1475 (0.7, [3M ‡ 1] ), 983 (20, [2M ‡ 1] ), 492
‡
74, [M ‡ 1] ), 436(51), 392(15), 293(23), 222(75), 91(100).
Boc-Val-Ala-Leu-OH. A suspension of Boc-Val-Ala-Leu-OBn (2.50 g, 5.1 mmol) and 10% Pd/C (0.1 g) in
MeOH (60 ml) was stirred under H
quant.) of Boc-Val-Ala-Leu-OH. Anal. data in agreement with those reported in [32].
Boc-Val-Ala-Leu-OMe (39). To a soln. of Boc-Val-Ala-Leu-OH (2.01 g, 5.1 mmol) in Et
was added, until the color of the soln. became yellow. Excess CH was destroyed by adding a few drops of
2
(balloon) at r.t. for 12 h. Filtration (Celite) and evaporation gave 2.01 g
(
2
2 2
O (60 ml), CH N
2
N
2
AcOH. Drying (MgSO
those reported in [32]. M.p. 159.5 ± 1628. [a]
4
) and evaporation gave 2.10 g (quant.) of 39. White solid. Anal. data in agreement with
r:t:
D
ˆ� 47.2 (c ˆ 1.9, CHCl
3
).
2 2
HCl ´ H-Val-Ala-Leu-OMe (40 ´ HCl). To a soln. of 39 (2.74 g, 6.59 mmol) in Et O (20 ml), sat. HCl/Et O
soln. (60 ml) was added and the mixture was stirred at r.t. for 12 h. After evaporation, 2.08 g (quant.) of 40 ´ HCl
were obtained. White foam. Anal. data in agreement with those reported in [32].
Boc-Ama(OBn)-OMe (13). According to GP 1, with DIPA (7.0 ml, 50 mmol), TMEDA (7.5 ml, 50 mmol),
BuLi (33.3 ml, 25.6 mmol) in THF (80 ml), and Boc-Gly-OBn (5.3 g, 20 mmol) in THF (60 ml). After workup,
the org. layer was treated with CH
2
N
2
, until the soln. became yellow. Excess CH
), evaporation, and purification by FC (hexane/AcOEt 3 :1) gave 5.04 g
): 1.43 (s, 9 H); 3.74 (s, 3 H); 5.03 (d, J ˆ 7.5, 1 H); 5.17 (AB, JAB
2 2
N was destroyed by adding
some drops of AcOH. Drying (MgSO
4
1
(
78%) of 13. H-NMR (300 MHz, CDCl
3
ˆ
13
1
2.4, 1 H); 5.27 (AB, JAB ˆ 12.2, 1 H); 5.55 (d, J ˆ 7, 1 H); 7.33 ± 7.35 (m, 5 H). C-NMR (75 MHz, CDCl
3
):
28.14 (Me); 53.17 (Me); 57.39 (CH); 67.90 (CH ); 80.70 (C); 128.05 (CH); 128.23 (CH); 128.52 (CH); 134.76
2
(C); 154.65 (C); 166.36 (C); 166.91 (C).
H-Ama(OMe)-OBn ´ HCl (41 ´ HCl). To a soln. of 13 (4.90 g, 15.1 mmol) in Et
2
2
O (10 ml), sat. HCl/Et O
soln. (50 ml) was added, and the mixture was stirred at r.t. for 12 h. After evaporation, 3.89 g (quant.) of 41 ´
1
HCl were obtained. White oil. H-NMR (300 MHz, CDCl
3
): 3.74 (s, 3 H); 5.16 (m, 3 H); 7.25 ± 7.33 (m, 5 H);
1
3
8
.40 ± 9.50 (br. s, 3 H). C-NMR (75 MHz, CDCl
CH); 134.38 (C); 163.42 (C); 163.79 (C).
Boc-Leu-Ama(OMe)-OBn (42). According to GP 4, with Boc-Leu-OH ´ H
3
): 54.18 (Me); 55.82 (CH); 69.03 (CH ); 128.29 (CH); 128.49
2
(
2
O (3.98 g, 16 mmol), 41 ´ HCl
(
(
(
5
2
3.70 g, 14.2 mmol), NMM (3.5 ml, 32 mmol), HOBt (2.16 g, 16 mmol), and EDC (3.45 g, 18 mmol) in THF
1
100 ml). FC (hexane/AcOEt 1 : 1): 6.44 g (97%) of 42. H-NMR (300 MHz, CDCl
3
): 0.90 ± 0.94 (m, 6 H); 1.43
s, 9 H); 1.43 ± 1.51 (m, 1 H); 1.61 ± 1.75 (m, 2 H); 3.74 (s, 3 H); 4.15 ± 4.30 (br. m, 1 H); 4.85 ± 4.93 (br. m, 1 H);
.16 ± 5.28 (m, 3 H); 7.15 ± 7.21 (br. m, 1 H); 7.30 ± 7.38 (m, 5 H). 13C-NMR (75 MHz, CDCl
2.93 (Me); 24.61 (CH); 28.22 (Me); 40.99 (CH ); 52.68 (CH); 53.27 (Me); 56.21 (CH); 68.04 (CH
): 21.77 (Me);
); 80.25
3
2
2
(
C); 128.10 (CH); 128.52 (CH); 128.55 (CH); 134.69 (C); 165.76 (C); 165.81 (C); 166.32 (C); 172.46 (C). FAB-
‡
‡
MS: 873 (11, [2M ‡ 1] ), 773(3), 437 (58, [M ‡ 1] ), 381(100), 337(80), 224(30), 175(21).
HCl ´ H-Leu-Ama(OMe)-OBn (43 ´ HCl). A soln. of 42 (2.0 g, 4.56 mmol) in sat. HCl/Et
2
O (30 ml) was
; 2
1
stirred at r.t. for 12 h and then evaporated to yield 1.70 g (quant.) of 43 ´ HCl. H-NMR (300 MHz, CDCl
3
epimers): 0.89 ± 0.99 (m, 6 H); 1.65 ± 1.90 (m, 3 H); 3.69, 3.71 (2s, 3 H); 4.40 ± 4.55 (br. m, 1 H); 5.10 ± 5.36
(
(
1
m, 3 H); 7.31 (m, 5 H); 8.25 ± 8.45 (m, 4 H). 13C-NMR (75 MHz, CD
3
OD; 2 epimers): 22.22 (Me); 23.19
Me); 25.39 (CH); 41.80 (CH
2
); 52.88 (CH); 53.92 (Me); 57.80 (CH); 69.24 (CH
2
); 129.64 (CH); 129.71 (CH);
‡
29.94 (CH); 136.91 (C); 167.47, 167.53 (C); 168.03 (C); 171.24 (C). FAB-MS: 674 (5, [2M ‡ 1] ), 338 (100,
‡
[
M ‡ 1] ), 306(26), 288(12), 154(32).

Helvetica Chimica Acta ± Vol. 81 (1998)
1873
Boc-Ala-Leu-Ama(OMe)-OBn (44). According to GP 2, with Boc-Ala-OH (0.87 g, 4.6 mmol), 43 ´ HCl
(
1.70 g, 4.56 mmol), NMM (1.01 ml, 9.2 mmol), and isobutyl chloroformate (0.6 ml, 4.6 mmol) in THF (80 ml),
1
and DMF (10 ml). After workup, 2.25 g (97%) of 44 were obtained. H-NMR (300 MHz, CDCl
3
; 2 epimers):
0
4
7
(
.87 ± 0.93 (m, 6 H); 1.32, 1.33 (2d, J ˆ 6.8, 6.8, 3 H); 1.42 (s, 9 H); 1.51 ± 1.69 (m, 3 H); 3.744, 3.749 (2s, 3 H);
.10 ± 4.20 (m, 1 H); 4.50 ± 4.57 (m, 1 H); 5.00 (d, J ˆ 6.5, 1 H); 5.15 ± 5.28 (m, 3 H); 6.63 (d, J ˆ 6.8, 1 H); 7.17 ±
1
3
.19 (br. m 1 H); 7.31 ± 7.39 (m, 5 H). C-NMR (75 MHz, CDCl
Me); 24.54 (CH); 28.22 (Me); 40.56, 40.63 (CH ); 49.95 (CH); 51.25 (CH); 53.27 (Me); 56.23 (CH); 68.04
); 80.24 (C); 128.13 (CH); 128.53 (CH); 134.69 (C); 155.56 (C); 165.68 (C); 166.25 (C); 171.72 (C); 172.86
3
; 2 epimers): 17.88 (Me); 21.75 (Me); 22.92
2
(
(
CH
2
‡
‡
‡
C). FAB-MS: 1523 (1, [3M ‡ 1] ), 1015 (67, [2M ‡ 1] ), 508 (100, [M ‡ 1] ), 452(98), 408(12), 229(52),
2
24(59), 201(33).
H-Ala-Leu-Ama(OMe)-OBn ´ HCl (45 ´ HCl). A soln. of 44 (2.20 g, 4.34 mmol) in sat. HCl/Et
was stirred at r.t. for 10 h and then evaporated to yield 1.92 g (quant.) of 45 ´ HCl. H-NMR (300 MHz, CD
2
O (100 ml)
OD;
1
3
2
(
epimers): 0.90 ± 0.97 (m, 6 H); 1.50 (d, J ˆ 7.1, 3 H); 1.52 ± 1.73 (m, 3 H); 3.73, 3.74 (2s, 3 H); 3.96 ± 4.05
m, 1 H); 4.53 ± 4.59 (m, 1 H); 5.15 ± 5.28 (m, 3 H); 7.31 ± 7.36 (m, 5 H). 13C-NMR (75 MHz, CD
OD; 2
); 50.03, 50.26 (CH); 53.07 (Me);
3
epimers): 17.82 (Me); 22.03 (Me); 23.50 (Me); 25.90 (CH); 41.86, 41.90 (CH
2
5
1
2
3.80 (CH); 57.77, 57.80 (CH); 69.11 (CH ); 129.63 (CH); 129.85 (CH); 129.92 (CH); 136.97 (C); 167.65,
‡
‡
67.76 (C); 168.20, 168.31 (C); 171.43 (C); 174.68 (C). FAB-MS: 1222 (5, [3M ‡ 1] ), 815 (60, [2M ‡ 1] ), 408
‡
(
100, [M ‡ 1] ), 337(10), 224(19), 185(47).
Boc-Val-Ala-Leu-Ama(OMe)-OBn (46). According to GP 2, with Boc-Val-OH (0.956 g, 4.4 mmol), 45 ´
HCl (1.90 g, 4.3 mmol), NMM (0.96 ml, 8.8 mmol), isobutyl chloroformate (4.5 ml, 4.4 mmol), and THF
(
(
1
70 ml). After workup, 2.45 g (94%) 46 were obtained. The residue was stirred in AcOEt for 1 h at 608. 1.97 g
1
77%) of 46. White solid. H-NMR (300 MHz, CDCl
3
; 2 epimers): 0.85 ± 0.93 (m, 12 H); 1.34 (d, J ˆ 7, 3 H);
.42 (s, 9 H); 1.50 ± 1.70 (m, 3 H); 2.04 ± 2.13 (m, 1 H); 3.71, 3.74 (2s, 3 H); 4.00 ± 4.10 (m, 1 H); 4.57 ± 4.64
(
(
2
5
m, 1 H); 4.68 ± 4.73 (m, 1 H); 5.10 ± 5.35 (m, 4 H); 6.97 ± 7.06 (m, 2 H); 7.29 ± 7.37 (m, 5 H); 7.52 ± 7.61
1
3
m, 1 H). C-NMR (75 MHz, CDCl
3
; 2 epimers): 17.73 (Me); 18.50 (Me); 19.26 (Me); 22.02 (Me); 22.86,
2.89 (Me); 24.63, 24.65 (CH); 28.33 (Me); 30.98, 31.03 (CH); 41.05, 41.11 (CH ); 48.78, 48.83 (CH); 51.36,
1.39 (CH); 53.22 (Me); 56.22, 56.26 (CH); 59.84 (CH); 67.99, 68.03 (CH ); 79.89 (C); 128.09 (CH); 128.17
2
2
(
(
3
CH); 128.52, 128.58 (CH); 134.86 (C); 156.05 (C); 165.86, 165.96 (C); 166.38, 166.49 (C); 171.70 (C); 172.02
‡
‡
‡
C); 172.28 (C). FAB-MS: 1820 (0.9, [3M ‡ 1] ), 1213 (28, [2M ‡ 1] ), 607 (100, [M ‡ 1] ), 507(25), 384(16),
37(31), 328(44), 215(26).
Boc-Val-Ala-Leu-Ama(OMe)-OH (47). A mixture of 46 (1.012 g, 2.0 mmol), 10% Pd/C (50 mg), and
MeOH (50 ml) was stirred under a H
2
(balloon) at r.t for 12 h. Filtration (Celite) and evaporation gave 1.04 g
)DMSO; 2 epimers): 0.78 ± 0.88 (m, 12 H); 1.17 ± 1.23 (m, 3 H); 1.37
1
(
(
quant.) of 47. H-NMR (300 MHz, (D
s, 9 H); 1.42 ± 1.47 (m, 2 H); 1.54 ± 1.65 (m, 1 H); 1.90 ± 1.96 (m, 1 H); 3.61, 3.62 (2s, 3 H); 3.70 ± 3.92 (m, 3 H);
6
4
0
1
.30 ± 4.42 (m, 2.5 H); 4.65 ± 4.70 (br. m, 0.5 H); 6.73 (d, J ˆ 8.9, 0.5 H); 7.85 ± 7.99 (br. m, 1 H); 7.97 (d, J ˆ 8.4,
13
.5 H); 8.07 ± 8.34 (m, 1.5 H). C-NMR (75 MHz, (D
9.10 (Me); 21.32, 21.54 (Me); 22.92 (Me); 23.02 (Me); 23.99 (CH); 28.10 (Me); 30.33 (CH); 40.59, 40.99
); 47.73 (CH); 50.41, 50.56 (CH); 50.66, 51.57 (CH); 52.28, 52.36 (Me); 56.41 (CH); 58.95, 59.41 (CH);
7.96 (C); 155.38 (C); 166.81 (C); 167.67, 167.80 (C); 170.10, 170.76 (C); 171.76, 171.86 (C); 171.95, 172.23 (C).
6
)DMSO; 2 epimers): 17.85 (Me); 18.14, 18.30 (Me);
(CH
2
7
‡
‡
‡
FAB-MS: 1638(22), 1616(25), 1077(49), 1055 (46, [2M ‡ 23] ), 539 (100, [M ‡ 23] ), 517 (43, [M ‡ 1] ),
4
43(21), 417(21), 395(35), 328(25), 247(35), 215(27), 117(45), 116(30).
Boc-Val-Ala-Leu-Ama(OMe)-Val-Ala-Leu-OMe (8). According to GP 4, with 47 (1.188 g, 2.3 mmol), 40 ´
HCl (0.809 g, 2.3 mmol), HOBt (0.31 g, 2.3 mmol), NMM (2.5 ml, 2.3 mmol), EDC (0.55 g, 2.8 mmol), and
THF (100 ml); 1 h at 08 and 24 h at r.t. The mixture was concentrated under h.v., and the residue was stirred for
2
h in H
2
O. The white precipitate was filtered off and washed with H
2
O. The solid was then stirred for 2 h in
1
AcOEt at 608. Drying under h.v.: 0.973 g (50%) of 8. White powder. H-NMR (300 MHz, (D
6
)DMSO; 2
epimers): 0.74 ± 0.85 (m, 24 H); 1.14 (d, J ˆ 6.8, 3 H); 1.16 (d, J ˆ 7.1, 3 H); 1.34 (s, 9 H); 1.38 ± 1.58 (m, 6 H);
1.87 ± 1.95 (m, 2 H); 3.57 (s, 3 H); 3.59, 3.62 (2s, 3 H); 3.73 ± 3.78 (m, 1 H); 4.15 ± 4.44 (m, 5 H); 5.21, 5.33
(
2d, J ˆ 7.7, 8.1, 1 H); 6.69 (d, J ˆ 8.7, 1 H); 7.81, 7.83 (2d, J ˆ 7.7, 7.7, 1 H); 7.97, 7.99 (2d, J ˆ 5.9, 7.4, 1 H);
8
1
(
.06, 8.15 (2d, J ˆ 8.4, 7.1, 1 H); 8.16 (d, J ˆ 7.7, 1 H); 8.20, 8.27 (2d, J ˆ 7.4, 8.4, 1 H); 8.35, 8.53 (2d, J ˆ 7.8, 9.3,
1
3
6
H). C-NMR (75 MHz, (D )DMSO; 2 epimers): 17.55, 17.76 (Me); 17.85, 17.95 (Me); 18.19 (Me); 18.89
Me); 19.10 (Me); 21.14 (Me); 21.30 (Me); 21.37 (Me); 22.72 (Me); 22.97 (Me); 23.11 (Me); 23.99 (CH); 24.05
); 47.74 (CH); 50.11 (CH); 50.71 (CH); 51.81
(
CH); 28.11 (Me); 30.33 (CH); 30.80, 31.06 (CH); 40.68 (CH
2
(
1
4
Me); 52.46 (Me); 56.15 (CH); 57.46 (CH); 59.45 (CH); 78.05 (C); 155.63, 155.66 (C); 165.28 (C); 168.20,
68.42 (C); 169.86 (C); 170.25, 171.04 (C); 172.14 (C); 172.40 (C); 172.52 (C); 173.11 (C). GC: 3.28 (l-Ala);
.55 (l-Val); 5.16 (Gly); 7.75 (l-Leu).

1874
Helvetica Chimica Acta ± Vol. 81 (1998)
5
. Alkylations. General Procedure (GP 5). Dried LiBr (if used) and the peptide were dissolved in THF and
cosolvent (if used). The soln. was cooled to 08 (ice bath) under Ar. Then, the base (NaOMe, as a soln in MeOH,
or solid t-BuOK) was added. After 10 min, the appropriate electrophile (3 equiv.) was added. The mixture was
worked up by addition of 1n HCl and AcOEt. The org. phases were washed twice with sat. aq. NaCl soln. All aq.
layers were extracted twice with AcOEt. The combined org. phases were dried (MgSO
.1. Alkylation 1. Boc-Leu-(CO Me)Ala-Leu-OMe (48a/b). According to GP 5, with 1 (1.50 g, 3.27 mmol),
MeI (0.62 ml, 9.81 mol), NaOMe soln. (3.5 ml, 3.5 mmol), and THF (40 ml); 2.5 h. FC (hexane/AcOEt 1 :1):
.34 g (84%) of 48a/b as a 1:1 mixture of epimers. 1H-NMR (400 MHz, CDCl
; 2 epimers): 0.84 ± 0.96
m, 12 H); 1.45 (s, 9 H); 1.48 ± 1.72 (m, 6 H); 1.80 (s, 3 H); 3.71, 3.73 (2s, 3 H); 3.75, 3.77 (2s, 3 H); 4.04 ± 4.13
4
) and evaporated.
5
2
1
3
(
(
(
(
(
1
3
1
3
m, 1 H); 4.53 ± 4.59 (m, 1 H); 4.88 (m, 1 H); 6.77, 6.84 (2d, J ˆ 7, 7, 1 H); 7.46, 7.53 (2s, 1 H). C-NMR
100 MHz, CDCl ; 2 epimers): 21.65, 21.68 (Me); 21.84, 21.95 (Me); 22.70, 22.79 (Me); 22.84 (Me); 22.97, 22.99
Me); 24.66, 24.76 (CH); 24.85, 24.90 (CH); 28.26 (Me); 40.87 (CH ); 51.29, 51.36 (CH); 52.36 (Me); 52.96
Me); 53.35, 53.46 (CH); 62.75, 63.00 (C); 80.15, 80.32 (C); 155.57, 155.78 (C); 167.39, 167.63 (C); 170.87,
3
2
‡
‡
70.95 (C); 171.74 (C); 172.49, 172.58 (C). FAB-MS: 510 (67, [M ‡ 23] ), 488 (68, [M ‡ 1] ), 432(41),
88(25), 275(83), 146(55), 86(100).
2
Boc-Leu-(CO Me)Abu-Leu-OMe (49a/b). According to GP 5, with 1 (0.473 g, 1 mmol), EtI (0.25 ml,
3
mmol), NaOMe soln. (1.2 ml, 1.2 mmol), and THF (15 ml); 16 h. FC (hexane/AcOEt 2 :1): 0.317 g (61%) of
1
49a/b as a 1:1 mixture of epimers. H-NMR (200 MHz, CDCl
3
; 2 epimers): 0.7 ± 0.85 (m, 3 H); 1.4 (s, 9 H); 1.4 ±
1
4
.8 (m, 6 H); 2.15 ± 2.3 (m, 1 H); 2.4 ± 2.6 (m, 1 H); 3.67, 3.69 (s, 3 H); 3.71, 3.74 (s, 3 H); 4.00 ± 4.17 (m, 1 H);
.45 ± 4.60 (m, 1 H); 4.8 ± 5.0 (br. m, 1 H); 6.65 ± 6.85 (br. m, 1 H); 7.45, 7.55 (2s, 1 H). 13C-NMR (50 MHz,
CDCl ; 2 epimers): 7.38, 7.51 (Me); 21.36, 21.60 (Me); 21.66, 21.80 (Me); 22.69 (Me); 22.82 (Me); 24.52, 24.66
CH); 24.74 (CH); 26.23, 26.59 (CH ); 28.12 (Me); 40.47, 40.61 (CH ); 40.73 (CH ); 51.17 (CH); 52.23, 52.97
Me); 53.07, 53.25 (Me); 66.84, 67.17 (C); 166.63, 166.89 (C); 170.68, 170.82 (C); 171.65, 171.70 (C); 172.52 (C);
3
(
(
2
2
2
‡
‡
‡
1
2
72.65 (C). FAB-MS: 1003 (8, [2M ‡ 1] ), 524 (14, [M ‡ 23] ), 502 (100, [M ‡ 1] ), 446(40), 402(12),
89(22), 115(12).
Boc-Leu-(Bu)Ama(OMe)-Leu-OMe (50a/b). According to GP 5, with 1 (0.473 g, 1 mmol), BuI (0.34 ml,
3
mmol), 1.2 ml of NaOMe soln. (1m in MeOH), and THF (15 ml); 10 h. FC (hexane/AcOEt 3 :1): 0.164 g
1
(
31%) of 50a/b as a 1:1 mixture of epimers. H-NMR (200 MHz, CDCl
3
; 2 epimers): 0.75 ± 0.90 (m, 15 H);
0.90 ± 1.65 (m, 10 H); 1.38, 1.39 (2s, 9 H); 2.05 ± 2.25 (m, 1 H); 2.25 ± 2.55 (m, 1 H); 3.64, 3.65, 3.67, 3.70
(
(
2
(
6
(
4s, 6 H); 3.95 ± 4.15 (m, 1 H); 4.45 ± 4.55 (m, 1 H); 4.85 ± 5.00 (m, 1 H); 6.70 ± 6.95 (m, 1 H); 7.40 ± 7.55
1
3
m, 1 H). C-NMR (75 MHz, CDCl
3
; 2 epimers): 13.62 (Me); 21.25 (Me); 21.59 (Me); 21.75 (Me); 22.12 (Me);
); 22.74 (Me); 24.44, 24.51 (CH); 24.62, 24.68 (CH); 25.11 (CH ); 25.25 (CH ); 25.37 (Me); 28.06
Me); 32.87 (CH ); 40.41, 40.57 (CH ); 40.75 (CH ); 51.09 (CH); 52.00, 52.15 (CH); 52.99 (Me); 53.15 (Me);
6.24, 66.59 (CH ); 80.11, 80.38 (C); 155.51 (C); 166.67, 166.83, 166.96 (C); 170.66, 170.80 (C); 171.60, 171.69
2.65 (CH
2
2
2
2
2
2
2
‡
‡
C); 172.45, 172.51 (C). FAB-MS: 1059 (2, [2M ‡ 1] ), 530 (75, [M ‡ 1] ), 474(35), 430(14), 317(59),
2
57(26), 144(100), 86(79).
Boc-Leu-(All)Ama(OMe)-Leu-OMe (51a/b). According to GP 5, with 1 (0.473 g, 1 mmol), allyl bromide
(
(
(
0.25 ml, 3 mmol), NaOMe soln. (1.2 ml, 1.2 mmol), and THF (15 ml); 3 h. FC (hexane/AcOEt 2 :1): 0.417 g
1
81%) of 51a/b as a 1:1 mixture of epimers. H-NMR (400 MHz, CDCl
3
; 2 epimers): 0.89 ± 0.96 (m, 12 H); 1.45
s, 9 H); 1.52 ± 1.73 (m, 6 H); 3.00 ± 3.09 (m, 1 H); 3.14 ± 3.22 (m, 1 H); 3.71, 3.72 (2s, 3 H); 3.76, 3.78 (2s, 3 H);
4
6
2
.10 ± 4.13 (m, 1 H); 4.53 ± 4.59 (m, 1 H); 4.85 (d, J ˆ 7, 1 H); 5.09 ± 5.14 (m, 2 H); 5.51 ± 5.62 (m, 1 H); 6.83,
13
.96 (2d, J ˆ 9, 9, 1 H); 7.39, 7.45 (s, 1 H). C-NMR (100 MHz, CDCl
1.88 (Me); 22.80, 22.82 (Me); 22.97 (Me); 24.68 (CH); 24.81 (CH); 28.26 (Me); 37.43, 37.77 (CH
); 40.92 (CH ); 5.28 (CH); 52.32 (Me); 53.36 (Me); 53.47 (CH); 65.95 (C); 120.08, 120.40 (Me); 130.79,
3
; 2 epimers): 21.50, 21.64 (Me); 21.76,
2
); 40.88
(CH
2
2
‡
1
5
31.11 (CH); 166.01, 166.40 (C); 170.06, 170.20 (C); 171.66 (C); 172.48 (C). FAB-MS: 536 (100, [M ‡ 23] ),
‡
14 (60, [M ‡ 1] ), 458(33), 414(15), 313(27).
2
Boc-Leu-(CO Me)Phe-Leu-OMe (52a/b). According to GP 5, with 1 (0.473 g, 1 mmol), BnBr (0.35 ml,
3
5
mmol), NaOMe soln. (1.2 ml, 1.2 mmol), and THF (15 ml); 4 h. FC (hexane/AcOEt 1:1): 0.486 g (86%) of
1
2a/b as a 1 :1 mixture of epimers. H-NMR (400 MHz, CDCl
3
; 2 epimers): 0.90 ± 0.87 (m, 12 H); 1.42 (s, 3 H);
1.55 ± 1.71 (m, 6 H); 3.71 ± 3.72 (m, 2 H); 3.73, 3.75 (2s, 3 H); 3.79, 3.81 (2s, 3 H); 4.02 ± 4.06 (m, 1 H); 4.53 ±
4
.60 (m, 1 H); 4.79 ± 4.80 (m, 1 H); 6.83, 7.17 (2d, J ˆ 8, 8, 1 H); 7.00 ± 7.05, 7.20 ± 7.24 (2m, 5 H); 7.27, 7.34
1
3
(2s, 1 H). C-NMR (100 MHz, CDCl
(Me); 24.67 (CH); 24.84 (CH); 28.22, 28.24 (Me); 37.65 (CH
52.25, 52.35 (Me); 53.30, 53.45 (Me); 54.00 (CH); 67.59 (C); 80.65 (C); 127.14, 127.25 (CH); 128.29, 128.30
3
; 2 epimers): 21.38, 21.45 (Me); 21.60, 21.66 (Me); 22.86 (Me); 23.07
2
); 40.63 (CH ); 41.67 (CH ); 51.30, 51.36 (CH);
2
2
(
1
CH); 129.89, 130.00 (CH); 135.36 (C); 155.97 (C); 166.51 (C); 170.03, 170.18 (C); 171.16, 171.58 (C); 172.45,
72.65 (C). FAB-MS: 586 (36, [M ‡ 23] ), 564 (40, [M ‡ 1] ), 508(23), 363(25), 291(25), 178(100).
‡
‡