A cis amide bond surrogate incorporating 1,2,4-triazole.

Article abstract of DOI:10.1021/jo010904i

A novel cis amide bond surrogate incorporating 1,2,4-triazole was designed and synthesized by the reaction of a thionotripeptide, formic hydrazide, and mercury(II) acetate. This method of surrogate formation was also applicable to a cyclic thionopeptide.

Full text of DOI:10.1021/jo010904i

3266
J . Org. Chem. 2002, 67, 3266-3271
A cis Am id e Bon d Su r r oga te In cor p or a tin g 1,2,4-Tr ia zole
Yukio Hitotsuyanagi, Shuichi Motegi, Haruhiko Fukaya, and Koichi Takeya*
School of Pharmacy, Tokyo University of Pharmacy and Life Science, 1432-1 Horinouchi,
Hachioji, Tokyo 192-0392, J apan
takeyak@ps.toyaku.ac.jp
Received September 5, 2001
A novel cis amide bond surrogate incorporating 1,2,4-triazole was designed and synthesized by the
reaction of a thionotripeptide, formic hydrazide, and mercury(II) acetate. This method of surrogate
formation was also applicable to a cyclic thionopeptide.
The peptide analogues into which a cis amide bond
surrogate has been incorporated are useful for the studies
of the active conformation and/or the topology of the
active site of original peptides. 1,5-Disubstituted tetrazole
is known as a cis amide bond surrogate (Figure 1),1,2 and
it has been incorporated into bradykinin,3 CCK-B recep-
tor ligands,4 somatostatin,5 leucine-enkephalin,6 and TRH
analogues7 for their biological activity studies. Tetrazole
is a good cis amide bond surrogate. However, it can be
formed only in dipeptides, and the elongation of the
peptide chains by addition of amino acid residues or
peptides at the N-terminus is not easy, as it readily forms
a diketopiperazine ring.2,3 We considered that 1,2,4-
triazole might make a good cis amide bond surrogate, as
it is formed via an easily accessible thionopeptide. The
present paper describes preparation of several triazole
surrogate-containing peptides via their thionopeptides.
Thionopeptides are known to be readily prepared by
the reaction of benzotriazole thioacylating agents with
amino acid esters.8 By using this method, as shown in
Scheme 1, thionotripeptides 3a -m were prepared from
benzotriazole thioacylating agents 1 and dipeptide esters
2 in moderate to excellent yields. When thionotripeptide
3a was treated with 5 equiv of formic hydrazide and 1.5
equiv of mercury(II) acetate in acetonitrile at room
temperature for 2 h, triazolotripeptide 4a was obtained
in 67% yield. The presence of the triazole ring in 4a was
confirmed by the characteristic resonances of the methine
proton (δ 8.28, br s, 1H) and the methine (δ 141.56) and
quaternary (δ 154.57) carbons of the triazole ring in the
NMR spectra. Triazolotripeptides have an advantage over
their dipeptide analogues in that they do not form
diketopiperazine during the extension reaction of the
peptide chain at the N-terminus. In the same manner,
thionotripeptides 3b-m were converted into their tria-
F igu r e 1.
Sch em e 1a
(1) Yu, K.-L.; J ohnson, R. L. J . Org. Chem. 1987, 52, 2051-2059.
(2) Zabrocki, J .; Smith, G. D.; Dunbar, J . B., J r.; Iijima, H.; Marshall,
G. R. J . Am. Chem. Soc. 1988, 110, 5875-5880.
a
R1, R2, R3: See Table 1
(3) Zabrocki, J .; Dunbar, J . B., J r.; Marshall, K. W.; Toth, M. V.;
Marshall, G. R. J . Org. Chem. 1992, 57, 202-209.
(4) Boteju, L. W.; Zalewska, T.; Yamamura, H. I.; Hruby, V. J .
Bioorg. Med. Chem. Lett. 1993, 3, 2011-2016.
zolotripeptides 4b-m (Table 1). This method was found
to be satisfactory for those thionopeptides having oxida-
tion-sensitive residues such as unprotected tryptophan
(entry 5), methionine (entry 8), and tyrosine (entry 9).
The side chains of the thionoamino acid residues in
tripeptides appear to affect the yields of triazoles. When
the thionotripeptides contain thionovaline residue, the
yields of triazoles were quite low (entries 10 and 11),
(5) Beusen, D. D.; Slomczynska, J . Z. U.; Head, R. D.; Kao, J . L.-F.;
Marshall, G. R. Biopolymers 1995, 36, 181-200.
(6) Olczak, J .; Kaczmarek, K.; Maszczynska, I.; Lisowski, M.;
Stropova, D.; Hruby, V. J .; Yamamura, H. I.; Lipkowski, A. W.;
Zabrocki, J . Lett. Pept. Sci. 1998, 5, 437-440.
(7) Tong, Y.; Olczak, J .; Zabrocki. J .; Gershengorn, M. C.; Marshall,
G. R.; Moeller, K. D. Tetrahedron 2000, 56, 9791-9800.
(8) Shalaby, M. A.; Grote, C. W.; Rapoport, H. J . Org. Chem. 1996,
61, 9045-9048.
10.1021/jo010904i CCC: $22.00 © 2002 American Chemical Society
Published on Web 04/17/2002

A cis Amide Bond Surrogate
J . Org. Chem., Vol. 67, No. 10, 2002 3267
Ta ble 1. Tr ia zoles 4a -m fr om Th ion op ep tid es 3a -m
yield (%)
of 4
entry substrate R1
R2
R3
1
2
3
4
5
3a
3b
3c
3d
3e
Me Me
Me Bn
Bn
Me
Bn
Bn
indol-3-yl-
methyl
Bn
67
69
87
61
59
Me
H
Me i-Pr
Me Me
6
7
8
3f
3g
3h
Bn Me
Bn Bn
Bn 2-(methyl-
sulfanyl)ethyl
56
75
65
Me
Bn
9
3i
Bn Me
4-hydroxy-
benzyl
Bn
Bn
Bn
65
F igu r e 2.
10
11
12
13
3j
3k
3l
i-Pr i-Pr
i-Pr Me
13
18
59
60
H
H
Me
Bn
which may be attributed to the adjacent bulky isopropyl
group that hinders formic hydrazide from approaching
the thiocarbonyl group. Under the reaction conditions
used in the present experiment, no epimeric analogues
were detected.
Elongation of the amino acid chains at the N-terminus
of triazolopeptides was feasible, although it required a
rather long reaction time of 1-5 days. Triazolopeptide
4c was deprotected with 4 M HCl in dioxane, and then
it was subjected to a coupling reaction with N-Boc-D-
alanine, using 1-ethyl-3-(3′-(dimethylamino)propyl)carbo-
diimide‚HCl (EDC‚HCl) and 1-hydroxybenzotriazole
(HOBt) in chloroform to afford tetrapeptide 5c in 86%
yield. In the same manner, 4f and 4g were converted into
the corresponding tetrapeptides 5f and 6g, in yields of
81% and 82%, respectively. The structure of peptide 5f
was confirmed by X-ray crystallography.
3m
Me
tween D-Ala-1/Ala-2, Ala-2/Tyr-3, Tyr-3/Ala-4, Ala-4/Tyr-
5, Tyr-5/Tyr-6, and Tyr-6/D-Ala-1 in the major conformer
of 10 were determined to be trans, cis, cis, trans, trans,
and trans, respectively,11 which are trans, trans, trans,
trans, cis, and trans, respectively, in the original peptide
7.12 Peptides with conformational features of this type
are not known in the natural peptides of RA-series.
This new approach provides an efficient and practical
method for preparing a cis amide bond surrogate, which
may be of great value to peptide chemistry.
Exp er im en ta l Section
Gen er a l. THF was prepared by distillation over sodium
metal. Melting points are recorded uncorrected. 1H and 13C
NMR spectra were obtained at 300 K, unless otherwise noted.
1H chemical shifts in CDCl3, methanol-d4, and DMSO-d6 were
referenced to residual CHCl3 (7.26 ppm), CD2HOD (3.31 ppm),
and CD2HSOCD3 (2.50 ppm); 13C chemical shifts were refer-
enced to the solvent (CDCl3, 77.03 ppm; methanol-d4, 49.0
ppm; DMSO-d6, 39.5 ppm).
This method of surrogate formation is also applicable
to cyclic thionopeptides. Those cyclic thionopeptides were
readily prepared by treating the cyclic peptides with a
thionating reagent. A number of such cyclic thionopep-
tides have been prepared from biologically important
cyclic peptides.9 When a triazole unit is incorporated into
cyclic peptide backbones, however, the conformational
features of the surrogate-containing cyclic peptide ana-
logues may be different from those of the original
peptides. For example, treatment of RA-VII (7), an
antitumor bicyclic hexapeptide, with Lawesson’s reagent
afforded thioamide 8 and bis(thioamide) 9 in 80% and
3% yield, respectively10 (Figure 2). When 8 was treated
with formic hydrazide under the same conditions for 72
h, triazole 10 was obtained in 48% yield, in which the
peptide bond between Tyr-3 and Ala-4 is modified to cis.
Ben zotr ia zole Th ioa cyla tin g Agen t 1 (R1 ) H). This
compound was prepared according to the general procedure
reported in ref 8 via R-N-Boc-glycine 2-amino-5-nitroanilide
and R-N-Boc-glycine 2-amino-5-nitrothioanilide. Yield 88%;
orange amorphous powder; 1H NMR (400 MHz, CDCl3) δ 9.67
(d, 1H, J ) 2.0 Hz), 8.45 (dd, 1H, J ) 8.9, 2.0 Hz), 8.32 (d, 1H,
J ) 8.9 Hz), 5.44 (br s, 1H), 5.15 (d, 2H, J ) 6.1 Hz), 1.50 (s,
9H); 13C NMR (100 MHz, CDCl3) δ 203.33, 155.76, 149.62,
148.81, 131.88, 122.18, 121.53, 112.53, 80.54, 52.80, 28.33; IR
(KBr) νmax 3364, 2981, 2924, 1698, 1531, 1349, 1274, 1262,
1175, 1053, 999, 798, 735 cm-1; negative-FABMS m/z 336 [M
- H]-.
r-N-Boc-glycin e 2-a m in o-5-n itr oa n ilid e: yield 85%; yel-
1
The H NMR spectrum of 10 showed that, in CDCl3 at
1
low crystalline powder, mp 178-179 °C (hexane-EtOAc); H
315 K, 10 exists in two stable conformers in a ratio of
83:17. In the ROESY spectrum of 10, in the major
conformer, cross-peaks were observed between D-Ala-1
HR/Ala-2 NH, Tyr-3 HR/Ala-4 HR, Ala-4 HR/Tyr-5 NMe,
Tyr-5 HR/Tyr-6 NMe, Tyr-6 NMe/Tyr-6 HR, and Tyr-6
HR/D-Ala-1 NH. Accordingly, the peptide bonds be-
NMR (400 MHz, DMSO-d6) δ 9.27 (s, 1H), 8.11 (s, 1H), 7.86
(dd, 1H, J ) 9.0, 2.4 Hz), 7.05 (m, 1H), 6.75 (d, 1H, J ) 9.0
Hz), 6.46 (s, 2H), 3.76 (d, 2H, J ) 5.6 Hz), 1.39 (s, 9H); 13C
NMR (100 MHz, DMSO-d6) δ 169.28, 156.27, 149.78, 135.63,
123.37, 122.26, 121.24, 113.73, 78.50, 43.88, 28.32; IR (KBr)
(10) (a) Hitotsuyanagi, Y.; Suzuki, J .; Matsumoto, Y.; Takeya, K.;
Itokawa, H. J . Chem. Soc., Perkin Trans. 1 1994, 1887-1890. (b)
Hitotsuyanagi, Y.; Matsumoto, Y.; Sasaki, S.; Suzuki, J .; Takeya, K.;
Yamaguchi, K.; Itokawa, H. J . Chem. Soc., Perkin Trans. 1 1996,
1749-1755.
(11) No ROESY correlation was detected between Ala-2 HR/Tyr-3
HR, because the resonance of these protons had the same chemical
shifts, but the peptide bond between Ala-2/Tyr-3 was assigned to cis.
ROESY cross-peaks observed between Tyr-3 NMe/Tyr-3 Hâ and Tyr-3
NMe/Tyr-3 Hδ, and the absence of cross-peaks between Ala-2 HR/Tyr-3
NMe, Tyr-3 NMe/Tyr-3 HR, and Ala-2 Me/Tyr-3 NMe may provide
collateral evidence for the cis amide configuration between Ala-2/Tyr-
3.
(9) (a) Sherman, D. B.; Spatola, A. F.; Wire, W. S.; Burks, T. F.;
Nguyen, T. M.-D.; Schiller, P. W. Biochem. Biophys. Res. Commun.
1989, 162, 1126-1132. (b) Bock, M. G.; DiPardo, R. M.; Williams, P.
D.; Pettibone, D. J .; Clineschmidt, B. V.; Ball, R. G.; Veber, D. F.;
Freidinger, R. M. J . Med. Chem. 1990, 33, 2321-2323. (c) Seebach,
D.; Ko, S. Y.; Kessler, H.; Ko¨ck, M.; Reggelin, M.; Schmieder, P.;
Walkinshaw, M. D.; Bo¨lsterli, J . J .; Bevec, D. Helv. Chim. Acta 1991,
74, 1953-1990. (d) Kessler, H.; Geyer, A.; Matter, H.; Ko¨ck, M. Int. J .
Pept. Protein Res. 1992, 40, 25-40. (e) Kessler, H.; Matter, H.; Geyer,
A.; Diehl, H.-J .; Ko¨ck, M.; Kurz, G.; Opperdoes, F. R.; Callens, M.;
Wierenga, R. K. Angew. Chem., Int. Ed. Engl. 1992, 31, 328-330. (f)
Morita, H.; Nagashima, S.; Takeya, K.; Itokawa, H. Bioorg. Med. Chem.
Lett. 1995, 5, 677-680.
(12) Morita, H.; Kondo, K.; Hitotsuyanagi, Y.; Takeya, K.; Itokawa,
H.; Tomioka, N.; Itai, A.; Iitaka, Y. Tetrahedron 1991, 47, 2757-2772.

3268 J . Org. Chem., Vol. 67, No. 10, 2002
Hitotsuyanagi et al.
νmax 3385, 3350, 3293, 1698, 1680, 1624, 1587, 1528, 1480,
1308, 1167 cm-1; FABMS m/z 311 [M + H]+. Anal. Calcd for
3.05 (m, 2H), 2.29 (m, 1H), 1.45 (d, 3H, J ) 6.9 Hz), 1.43 (s,
9H), 0.97 (d, 3H, J ) 6.9 Hz), 0.94 (d, 3H, J ) 6.8 Hz); 13C
NMR (100 MHz, CDCl3) δ 205.85, 171.52, 169.31, 155.28,
135.39, 129.25, 128.62, 127.13, 80.18, 63.82, 56.23, 53.23,
52.31, 37.72, 30.60, 28.24, 21.48, 18.70, 18.42; IR (film) νmax
3307, 2974, 2933, 1733, 1686, 1663, 1520, 1497, 1440, 1367,
1218, 1168, 757 cm-1; FABMS m/z 488 [M + Na]+, 466 [M +
H]+. Anal. Calcd for C23H35N3O5S: C, 59.33; H, 7.58; N, 9.02.
Found: C, 59.05; H, 7.66; N, 8.83.
C
13H18N4O5: C, 50.32; H, 5.85; N, 18.06. Found: C, 50.25; H,
5.86; N, 17.98.
r-N-Boc-Glycin e 2-a m in o-5-n itr oth ioa n ilid e: yield 81%;
1
yellow crystalline powder, mp 158-159 °C (ether); H NMR
(400 MHz, DMSO-d6) δ 10.92 (br s, 1H), 7.94 (dd, 1H, J ) 9.1,
2.6 Hz), 7.90 (d, 1H, J ) 2.6 Hz), 7.13 (br s, 1H), 6.79 (d, 1H,
J ) 9.1 Hz), 6.42 (s, 2H), 4.10 (d, 2H, J ) 5.8 Hz), 1.41 (s,
9H); 13C NMR (100 MHz, DMSO-d6) δ 202.97, 155.95, 150.72,
135.38, 124.97, 124.81, 122.48, 113.97, 78.69, 51.52, 28.19; IR
(KBr) νmax 3349, 1668, 1634, 1515, 1490, 1390, 1333, 1304,
1250, 1160 cm-1; negative-FABMS m/z 325 [M - H]-. Anal.
Calcd for C13H18N4O4S: C, 47.84; H, 5.56; N, 17.17. Found:
C, 47.66; H, 5.60; N, 16.94.
Boc-Ala Ψ[CS-NH]Ala -Tr p -OMe (3e): yield 73%; amor-
phous solid; [R]26 -64.1° (c ) 0.39, MeOH); 1H NMR (400
D
MHz, CDCl3) δ 8.39 (br d, 1H, J ) 6.6 Hz), 8.21 (s, 1H), 7.49
(d, 1H, J ) 7.8 Hz), 7.34 (d, 1H, J ) 8.0 Hz), 7.18 (t, 1H, J )
7.9 Hz), 7.11 (t, 1H, J ) 7.9 Hz), 7.00 (d, 1H, J ) 2.3 Hz), 6.48
(br d, 1H, J ) 7.1 Hz), 5.09 (br s, 1H), 4.98 (m, 1H), 4.89 (m,
1H), 4.39 (m, 1H), 3.70 (s, 3H), 3.36-3.26 (m, 2H), 1.44 (s, 9H),
1.43 (d, 3H, J ) 6.8 Hz), 1.39 (d, 3H, J ) 7.0 Hz); 13C NMR
(100 MHz, CDCl3) δ 204.71, 172.15, 170.81, 155.30, 136.12,
127.45, 123.45, 122.10, 119.62, 118.37, 111.39, 109.20, 80.52,
56.76, 53.96, 53.14, 52.55, 28.29, 27.56, 21.65, 17.26; IR (film)
νmax 3320, 2979, 2932, 1734, 1685, 1519, 1442, 1367, 1216,
1166, 756 cm-1; FABMS m/z 499 [M + Na]+, 477 [M + H]+.
Anal. Calcd for C23H32N4O5S: C, 57.96; H, 6.77; N, 11.76.
Found: C, 57.58; H, 6.76; N, 11.45.
Gen er a l P r oced u r e for Rea ction of Ben zotr ia zole
Th ioa cyla tin g Agen ts 1 w ith Dip ep tid es 2. F or m a tion of
Th ion otr ip ep tid es 3a -m . N-Boc-protected dipeptide methyl
ester (1.0 mmol) was treated with 4 M HCl in dioxane (4.0
mL) at room temperature for 1 h. The mixture was evaporated
to dryness to give a residue, which was dissolved in THF (5
mL), and triethylamine (0.14 mL, 1.01 mmol) was added to
the solution at 0 °C. This solution was added dropwise to a
cooled solution (0 °C) of thioacylating agents 1 (1.0 mmol) in
15 mL of THF, and the mixture was stirred at this tempera-
ture for 20 min. The solvent was removed under reduced
pressure, and the residue was chromatographed (silica gel,
CHCl3/hexane/MeOH, 10/10/1 then MPLC, silica gel, EtOAc/
hexane, 2/3) to provide thionotripeptides 3a -m .
Boc-P h eΨ[CS-NH]Ala -P h e-OMe (3f): yield 90%; amor-
phous solid; [R]24 -32.5° (c ) 0.78, MeOH); 1H NMR (400
D
MHz, CDCl3) δ 8.14 (br d, 1H, J ) 6.7 Hz), 7.33-7.16 (m, 8H),
7.08 (d-like, 2H, J ) 8.2 Hz), 6.21 (d, 1H, J ) 7.6 Hz), 5.17 (br
s, 1H), 4.86 (m, 1H), 4.77 (m, 1H), 4.60 (m, 1H), 3.71 (s, 3H),
3.22-3.10 (m, 2H), 3.08 (d, 2H, J ) 5.9 Hz), 1.40 (s, 9H), 1.38
(d, 3H, J ) 7.0 Hz); 13C NMR (100 MHz, CDCl3) δ 202.71,
171.67, 170.42, 155.11, 136.39, 135.52, 129.20, 129.15, 128.61,
128.51, 127.18, 126.91, 80.37, 62.08, 53.84, 53.49, 52.41, 41.63,
37.73, 28.20, 17.20; IR (film) νmax 3302, 2979, 1731, 1686, 1454,
1440, 1366, 1217, 1169, 756, 700 cm-1; FABMS m/z 536 [M +
Na]+, 514 [M + H]+. Anal. Calcd for C27H35N3O5S: C, 63.14;
H, 6.87; N, 8.18. Found: C, 63.11; H, 6.97; N, 8.03.
Boc-Ala Ψ[CS-NH]Ala -P h e-OMe (3a ): yield 91%; amor-
phous solid; [R]24 -74.1° (c ) 0.91, MeOH); 1H NMR (400
D
MHz, CDCl3) δ 8.51 (br d, 1H, J ) 6.0 Hz), 7.32-7.21 (m, 3H),
7.09 (d-like, 2H, J ) 8.1 Hz), 6.45 (br d, 1H, J ) 7.1 Hz), 5.18
(br d, 1H, J ) 6.3 Hz), 4.98 (m, 1H), 4.85 (m, 1H), 4.43 (m,
1H), 3.72 (s, 3H), 3.17-3.05 (m, 2H), 1.48-1.37 (m, 6H), 1.43
(s, 9H); 13C NMR (100 MHz, CDCl3) δ 205.21, 171.71, 170.76,
155.16, 135.47, 129.18, 128.52, 127.07, 80.13, 55.98, 53.88,
53.42, 52.37, 37.74, 28.22, 21.76, 17.13; IR (film) νmax 3306,
Boc-P h eΨ[CS-NH]P h e-Ala -OMe (3g): yield 88%; amor-
phous solid; [R]24D -4.3° (c ) 0.67, MeOH); 1H NMR (400 MHz,
CDCl3) δ 8.13 (br s, 1H), 7.33-7.18 (m, 8H), 7.17-7.09 (m,
2H), 6.06 (br s, 1H), 5.13-5.04 (m, 2H), 4.62 (m, 1H), 4.39 (m,
1H), 3.69 (s, 3H), 3.37 (dd, 1H, J ) 13.5, 4.4 Hz), 3.17 (m, 2H),
2.84 (dd, 1H, J ) 13.5, 8.3 Hz), 1.33 (s, 9H), 1.26 (d, 3H, J )
7.2 Hz); 13C NMR (100 MHz, CDCl3) δ 202.30, 172.22, 168.52,
155.09, 136.13, 135.81, 129.33, 129.14, 128.69, 127.23, 127.20,
80.57, 63.02, 59.03, 52.35, 48.31, 41.08, 36.81, 28.10, 17.93;
IR (film) νmax 3305, 2979, 1717, 1685, 1508, 1498, 1454, 1367,
1217, 1164, 756, 700 cm-1; FABMS m/z 536 [M + Na]+, 514
[M + H]+. Anal. Calcd for C27H35N3O5S: C, 63.14; H, 6.87; N,
8.18. Found: C, 62.90; H, 7.01; N, 8.05.
2979, 1734, 1685, 1518, 1444, 1367, 1218, 1168, 757 cm-1
;
FABMS m/z 460 [M + Na]+, 438 [M + H]+. Anal. Calcd for
21H31N3O5S: C, 57.65; H, 7.14; N, 9.60. Found: C, 57.48; H,
C
7.31; N, 9.38.
Boc-Ala Ψ[CS-NH]P h e-Ala -OMe (3b): yield 83%; amor-
phous solid; [R]24 -15.3° (c ) 0.75, MeOH); 1H NMR (400
D
MHz, CDCl3) δ 8.53 (br d, 1H, J ) 7.2 Hz), 7.32-7.22 (m, 5H),
6.24 (br s, 1H), 5.20 (m, 1H), 5.11 (d, 1H, J ) 6.2 Hz), 4.50-
4.41 (m, 2H), 3.70 (s, 3H), 3.35 (dd, 1H, J ) 13.8, 5.0 Hz), 3.08
(dd, 1H, J ) 13.8, 8.0 Hz), 1.42 (d, 3H, J ) 6.9 Hz), 1.39 (s,
9H), 1.30 (d, 3H, J ) 7.2 Hz); 13C NMR (100 MHz, CDCl3) δ
204.80, 172.39, 168.96, 155.18, 135.92, 129.36, 128.69, 127.23,
80.51, 59.04, 57.53, 52.42, 48.35, 36.95, 28.20, 21.56, 17.98;
IR (film) νmax 3308, 2979, 1741, 1685, 1515, 1454, 1367, 1244,
1217, 1164, 756 cm-1; FABMS m/z 460 [M + Na]+, 438 [M +
H]+. Anal. Calcd for C21H31N3O5S: C, 57.65; H, 7.14; N, 9.60.
Found: C, 57.37; H, 7.04; N, 9.35.
Boc-P h eΨ[CS-NH]Met-P h e-OMe (3h ): yield 62%; amor-
phous solid; [R]26 -12.6° (c ) 0.47, MeOH); 1H NMR (400
D
MHz, CDCl3) δ 8.37 (br d, 1H, J ) 7.1 Hz), 7.35-7.09 (m,
10H), 6.65 (d, 1H, J ) 7.8 Hz), 5.19 (br d, 1H, J ) 6.9 Hz),
5.05, (m, 1H), 4.75 (m, 1H), 4.59 (m, 1H), 3.71 (s, 3H), 3.23-
3.02 (m, 4H), 2.53 (m, 2H), 2.15 (m, 1H), 2.03 (s, 3H), 1.98
(m, 1H), 1.39 (s, 9H); 13C NMR (100 MHz, CDCl3) δ 202.73,
171.33, 169.09, 155.11, 136.31, 135.50, 129.18, 129.14, 128.76,
128.63, 127.29, 127.03, 80.47, 62.63, 56.96, 53.50, 52.34, 41.39,
37.61, 29.61, 29.58, 28.23, 14.80; IR (film) νmax 3282, 2978,
Boc-Ala Ψ[CS-NH]Gly-P h e-OMe (3c): yield 92%; amor-
phous solid; [R]24D -6.7° (c ) 0.77, MeOH); 1H NMR (400 MHz,
CDCl3) δ 8.54 (br s, 1H), 7.33-7.21 (m, 3H), 7.09 (d-like, 2H,
J ) 8.1 Hz), 6.31 (br s, 1H), 5.13 (br s, 1H), 4.89 (m, 1H), 4.50
(m, 1H), 4.32 (dd, 1H, J ) 17.5, 4.7 Hz), 4.24 (dd, 1H, J )
17.5, 4.6 Hz), 3.74 (s, 3H), 3.15 (dd, 1H, J ) 13.9, 5.7 Hz),
3.11 (dd, 1H, J ) 13.9, 6.1 Hz), 1.46 (d, 3H, J ) 6.9 Hz), 1.44
(s, 9H); 13C NMR (100 MHz, CDCl3) δ 206.04, 171.83, 167.01,
155.26, 135.55, 129.19, 128.59, 127.15, 80.24, 56.25, 53.45,
52.49, 48.29, 37.78, 28.28, 21.88; IR (film) νmax 3310, 2979,
1741, 1685, 1509, 1497, 1438, 1366, 1217, 1167, 755, 700 cm-1
FABMS m/z 596 [M + Na]+, 574 [M + H]+. Anal. Calcd for
;
C
29H39N3O5S2‚0.25H2O: C, 60.23; H, 6.80; N, 7.27. Found C,
60.13; H, 6.88; N, 7.12.
Boc-P h eΨ[CS-NH]Ala -Tyr -OMe (3i): yield 48%; amor-
phous solid; [R]26 -21.0° (c ) 0.41, MeOH); 1H NMR (400
D
1738, 1686, 1521, 1444, 1367, 1247, 1219, 1168, 757 cm-1
FABMS m/z 446 [M + Na]+, 424 [M + H]+. Anal. Calcd for
20H29N3O5S: C, 56.72; H, 6.90; N, 9.92. Found: C, 56.54; H,
;
MHz, CDCl3) δ 8.26 (br d, 1H, J ) 6.7 Hz), 7.30-7.16 (m, 5H),
6.92 (d-like, 2H, J ) 8.4 Hz), 6.75 (d-like, 2H, J ) 8.4 Hz),
6.44 (d, 1H, J ) 7.9 Hz), 5.18 (br d, 1H, J ) 7.5 Hz), 4.88 (m,
1H), 4.74 (m, 1H), 4.64 (br m, 1H), 3.74 (s, 3H), 3.18 (d-like,
2H, J ) 6.3 Hz), 3.04-2.92 (m, 2H), 1.39 (s, 9H), 1.36 (d, 3H,
J ) 6.9 Hz); 13C NMR (100 MHz, CDCl3) δ 202.44, 172.02,
170.67, 155.40, 136.27, 130.41, 129.22, 128.64, 127.09, 126.90,
115.73, 80.85, 62.34, 54.01, 53.82, 52.59, 41.47, 37.08, 28.23,
17.29; IR (film) νmax 3309, 2979, 1732, 1684, 1516, 1442, 1367,
C
7.01; N, 9.74.
Boc-Ala Ψ[CS-NH]Va l-P h e-OMe (3d ): yield 88%; amor-
phous solid; [R]24 -96.4° (c ) 0.56, MeOH); 1H NMR (400
D
MHz, CDCl3) δ 8.39 (br d, 1H, J ) 7.6 Hz), 7.32-7.20 (m, 3H),
7.10 (d-like, 2H, J ) 8.2 Hz), 6.26 (d, 1H, J ) 7.6 Hz), 5.10 (br
s, 1H), 4.90-4.81 (m, 2H), 4.42 (m, 1H), 3.72 (s, 3H), 3.16-

A cis Amide Bond Surrogate
J . Org. Chem., Vol. 67, No. 10, 2002 3269
1219, 1170, 756 cm-1; FABMS m/z 552 [M + Na]+, 530 [M +
H]+. Anal. Calcd for C27H35N3O6S‚0.2H2O: C, 60.81; H, 6.62;
N, 7.88. Found C, 60.81; H, 6.90; N, 7.51.
) 6.7 Hz), 1.40 (s, 9H); 13C NMR (125 MHz, CDCl3) δ 171.43,
167.88, 155.64, 154.57, 141.56, 135.87, 128.92, 128.52, 126.94,
80.45, 53.61, 52.96, 52.27, 41.30, 37.66, 28.21, 19.94, 19.32;
IR (KBr) νmax 3276, 3213, 2981, 1756, 1709, 1698, 1531, 1523,
Boc-Va lΨ[CS-NH]Va l-P h e-OMe (3j): yield 91%; amor-
phous solid; [R]24 -93.9° (c ) 0.67, MeOH); 1H NMR (400
1455, 1366, 1268, 1250, 1217, 1201, 1173, 1064, 761, 705 cm-1
;
D
MHz, CDCl3) δ 8.29 (d, 1H, J ) 8.1 Hz), 7.33-7.21 (m, 3H),
7.11 (d-like, 2H, J ) 8.2 Hz), 6.31 (d, 1H, J ) 7.7 Hz), 5.18 (br
d, 1H, J ) 7.9 Hz), 4.93-4.83 (m, 2H), 4.07 (m, 1H), 3.73 (s,
3H), 3.11 (d, 2H, J ) 5.9 Hz), 2.38-2.23 (m, 2H), 1.44 (s, 9H),
1.01-0.88 (m, 12H); 13C NMR (100 MHz, CDCl3) δ 204.76,
171.49, 169.21, 155.63, 135.36, 129.23, 128.63, 127.16, 79.95,
66.81, 63.79, 53.27, 52.31, 37.74, 33.04, 30.57, 28.24, 19.58,
18.65, 18.53, 17.90; IR (film) νmax 3310, 2966, 1734, 1715,
FABMS m/z 446 [M + H]+. Anal. Calcd for C22H31N5O5: C,
59.31; H, 7.01; N, 15.72. Found: C, 59.25; H, 7.02; N, 15.64.
Da ta for 4b: colorless crystalline powder, mp 199-200 °C
1
(CHCl3-isopropyl ether); [R]25 -38.7° (c ) 1.00, MeOH); H
D
NMR (400 MHz, CDCl3) δ 8.61 (s, 1H), 7.98 (br s, 1H), 7.29-
7.19 (m, 3H), 7.01-6.92 (m, 2H), 5.88 (br s, 1H), 5.60 (br d,
1H, J ) 9.8 Hz), 4.55 (m, 1H), 4.12 (m, 1H), 3.77 (s, 3H), 3.40
(dd, 1H, J ) 14.3, 3.3 Hz), 3.20 (dd, 1H, J ) 14.3, 12.0 Hz),
1.37 (d, 3H, J ) 7.3 Hz), 1.33 (s, 9H), 0.94 (d, 3H, J ) 6.9 Hz);
13C NMR (100 MHz, CDCl3) δ 172.47, 167.41, 155.60, 155.35,
140.84, 135.36, 129.03, 128.95, 127.38, 80.38, 58.72, 52.36,
48.37, 40.27, 39.80, 28.20, 18.52, 17.53; IR (KBr) νmax 3261,
2983, 1743, 1672, 1549, 1509, 1454, 1367, 1316, 1284, 1252,
1210, 1181, 1074, 1062, 752, 702 cm-1; FABMS m/z 446 [M +
H]+. Anal. Calcd for C22H31N5O5: C, 59.31; H, 7.01; N, 15.72.
Found: C, 59.13; H, 6.94; N, 15.68.
1687, 1665, 1497, 1367, 1218, 1170, 1012, 757, 700 cm-1
FABMS m/z 516 [M + Na]+, 494 [M + H]+. Anal. Calcd for
25H39N3O5S: C, 60.83; H, 7.96; N, 8.51. Found: C, 60.54; H,
;
C
7.99; N, 8.35.
Boc-Va lΨ[CS-NH]Ala -P h e-OMe (3k ): yield 91%; amor-
phous solid; [R]26 -70.6° (c ) 0.57, MeOH); 1H NMR (400
D
MHz, CDCl3) δ 8.29 (d, 1H, J ) 6.9 Hz), 7.32-7.21 (m, 3H),
7.09 (d-like, 2H, J ) 8.2 Hz), 6.33 (d, 1H, J ) 8.6 Hz), 5.18 (br
s, 1H), 4.99 (m, 1H), 4.84 (m, 1H), 4.07 (m, 1H), 3.73 (s, 3H),
3.17-3.06 (m, 2H), 2.28 (m, 1H), 1.46 (d, 3H, J ) 7.0 Hz), 1.44
Da ta for 4c: amorphous solid; [R]24 +17.4° (c ) 1.99,
D
MeOH); 1H NMR (500 MHz, CDCl3) δ 8.17 (s, 1H), 7.84 (br d,
1H, J ) 5.5 Hz), 7.29-7.18 (m, 3H), 7.11 (d-like, 2H, J ) 8.3
Hz), 5.70 (br d, 1H, J ) 7.5 Hz), 5.01 (m, 1H), 4.90-4.68 (m,
3H), 3.70 (s, 3H), 3.18 (dd, 1H, J ) 13.9, 5.5 Hz), 3.05 (dd, 1H,
J ) 13.9, 8.1 Hz), 1.62 (d, 3H, J ) 6.9 Hz), 1.39 (s, 9H); 13C
NMR (125 MHz, CDCl3) δ 171.61, 165.48, 155.76, 155.54,
144.44, 136.02, 129.09, 128.48, 126.97, 80.10, 53.92, 52.31,
46.63, 41.24, 37.45, 28.22, 19.74; IR (film) νmax 3222, 2980,
1745, 1692, 1512, 1497, 1455, 1367, 1250, 1215, 1166, 755, 701
cm-1; FABMS m/z 432 [M + H]+; HRFABMS calcd for
(s, 9H), 0.92 (d, 3H, J ) 6.4 Hz), 0.91 (d, 3H, J ) 6.6 Hz); 13
C
NMR (100 MHz, CDCl3) δ 203.88, 171.74, 170.69, 155.62,
135.44, 129.22, 128.58, 127.14, 80.00, 66.13, 53.85, 53.51,
52.42, 37.81, 33.58, 28.29, 19.56, 17.75, 17.27; IR (film) νmax
3304, 2976, 1733, 1686, 1499, 1446, 1390, 1367, 1218, 1170,
757, 701 cm-1; FABMS m/z 488 [M + Na]+, 466 [M + H]+.
Anal. Calcd for C23H35N3O5S: C, 59.33; H, 7.58; N, 9.02.
Found: C, 59.11; H, 7.59; N, 8.84.
Boc-GlyΨ[CS-NH]Ala -P h e-OMe (3l): yield 71%; amor-
phous solid; [R]24 -62.4° (c ) 0.44, MeOH); 1H NMR (400
D
C
21H30N5O5 432.2247, found 432.2273.
MHz, CDCl3) δ 8.49 (br s, 1H), 7.33-7.21 (m, 3H), 7.10 (d-
like, 2H, J ) 8.2 Hz), 6.43 (br d, 1H, J ) 7.8 Hz), 5.12 (br s,
1H), 5.00 (m, 1H), 4.86 (m, 1H), 4.17 (dd, 1H, J ) 17.2, 6.2
Hz), 4.11 (dd, 1H, J ) 17.2, 6.2 Hz), 3.74 (s, 3H), 3.14 (dd, 1H,
J ) 14.0, 5.6 Hz), 3.09 (dd, 1H, J ) 14.0, 6.4 Hz), 1.46 (s, 9H),
1.45 (d, 3H, J ) 7.1 Hz); 13C NMR (100 MHz, CDCl3) δ 199.56,
171.62, 170.60, 156.09, 135.53, 129.27, 128.61, 127.17, 80.76,
53.82, 53.38, 52.45, 51.88, 37.81, 28.23, 17.08; IR (film) νmax
3315, 2979, 1682, 1523, 1444, 1367, 1276, 1248, 1217, 1167,
757, 702 cm-1; FABMS m/z 446 [M + Na]+, 424 [M + H]+.
Anal. Calcd for C20H29N3O5S: C, 56.72; H, 6.90; N, 9.92.
Found: C, 56.36; H, 7.01; N, 9.72.
Boc-GlyΨ[CS-NH]P h e-Ala -OMe (3m ): yield 67%; amor-
phous solid; [R]24D +6.9° (c ) 0.42, MeOH); 1H NMR (400 MHz,
CDCl3) δ 8.63 (br d, 1H, J ) 6.6 Hz), 7.34-7.23 (m, 5H), 6.05
(br s, 1H), 5.19 (m, 1H), 5.13 (br s, 1H), 4.46 (m, 1H), 4.24-
4.12 (m, 2H), 3.71 (s, 3H), 3.36 (dd, 1H, J ) 13.7, 5.0 Hz), 3.05
(dd, 1H, J ) 13.7, 8.4 Hz), 1.44 (s, 9H), 1.31 (d, 3H, J ) 7.2
Hz); 13C NMR (100 MHz, CDCl3) δ 199.65, 172.41, 168.95,
156.06, 135.83, 129.33, 128.70, 127.21, 80.73, 59.34, 52.44,
52.07, 48.33, 37.14, 28.21, 18.06; IR (film) νmax 3317, 2979,
1741, 1723, 1668, 1520, 1454, 1367, 1275, 1247, 1217, 1163,
756, 701 cm-1; FABMS m/z 446, [M + Na]+, 424 [M + H]+.
Anal. Calcd for C20H29N3O5S: C, 56.72; H, 6.90; N, 9.92.
Found: C, 56.44; H, 7.07; N, 9.68.
Da ta for 4d : colorless crystalline powder, mp 214-215 °C
1
(CHCl3-isopropyl ether); [R]24 -11.8° (c ) 1.00, CHCl3); H
D
NMR (500 MHz, CDCl3) δ 8.37 (br s, 1H), 8.02 (br s, 1H), 7.22-
7.13 (m, 3H), 7.05-6.95 (m, 2H), 6.44 (br s, 1H), 5.13-4.91
(m, 2H), 4.78 (m, 1H), 3.71 (s, 3H), 3.16 (dd, 1H, J ) 13.5, 5.5
Hz), 2.93 (m, 1H), 2.39 (m, 1H), 1.74 (br s, 3H), 1.40, (s, 9H),
1.11 (d, 3H, J ) 6.5 Hz), 0.74 (d, 3H, J ) 6.5 Hz); 13C NMR
(125 MHz, CDCl3) δ 171.26, 167.37, 155.72, 155.23, 141.59,
135.82, 128.87, 128.50, 126.95, 80.56, 63.51, 53.80, 52.20,
41.06, 37.72, 32.07, 28.25, 19.88, 19.16, 18.25; IR (KBr) νmax
3259, 2978, 1753, 1714, 1689, 1574, 1533, 1520, 1367, 1300,
1268, 1252, 1216, 1202, 1171, 1061, 703 cm-1; FABMS m/z 474
[M + H]+. Anal. Calcd for C24H35N5O5: C, 60.87; H, 7.45; N,
14.79. Found: C, 60.69; H, 7.42; N, 14.64.
Da ta for 4e: colorless crystalline powder, mp 223-224 °C
(CHCl3-isopropyl ether); [R]26 -8.2° (c ) 0.45, MeOH); 1H
D
NMR (400 MHz, CDCl3) δ 8.88 (s, 1H), 8.05 (br s, 1H), 7.47
(d-like, 2H, J ) 7.8 Hz), 7.35 (d, 1H, J ) 8.0 Hz), 7.14 (t, 1H,
J ) 7.9 Hz), 7.06 (t, 1H, J ) 7.9 Hz), 6.69 (br s, 1H), 5.97 (br
s, 1H), 5.38 (br s, 1H), 4.99-4.81 (m, 2H), 3.74 (s, 3H), 3.35
(dd, 1H, J ) 14.7, 4.7 Hz), 3.09 (m, 1H), 1.62-1.52 (m, 6H),
1.36 (s, 9H); 13C NMR (100 MHz, DMSO-d6) δ 172.02, 169.14,
155.05, 154.39, 143.29, 136.28, 127.13, 123.87, 121.20, 118.61,
118.04, 111.64, 108.97, 78.62, 53.65, 52.42, 52.05, 41.85, 28.24,
27.33, 19.75, 19.40; IR (KBr) νmax 3284, 2979, 1747, 1712, 1680,
1524, 1251, 1219, 1201, 1169, 1063, 741 cm-1; FABMS m/z 485
[M + H]+. Anal. Calcd for C24H32N6O5: C, 59.49; H, 6.66; N,
17.34. Found: C, 59.37; H, 6.64; N, 17.29.
Gen er a l P r oced u r e for P r ep a r a tion of Tr ia zoles 4a-m
fr om Th ion otr ip ep tid es 3a -m . To a suspension of thiono-
tripeptides 3a -m (0.16 mmol) and formic hydrazide (48.0 mg,
0.80 mmol) in MeCN (0.5 mL) was added mercury(II) acetate
(76.5 mg, 0.24 mmol), and the mixture was stirred at room
temperature for 2 h. Water (10 mL) was added to the mixture,
and the mixture was extracted with CHCl3 (3 × 10 mL). The
CHCl3 extract was washed with brine (5 mL), dried over
Na2SO4, and filtered, and the solvent was removed in vacuo.
The residue was chromatographed (MPLC, silica gel, hexane/
CHCl3/MeOH, 15:15:1) to provide triazoles 4a -m .
Da ta for 4f: colorless crystalline powder, mp 209-210 °C
1
(CHCl3-isopropyl ether); [R]24 +18.0° (c ) 0.41, MeOH); H
D
NMR (400 MHz, CDCl3) δ 7.74 (s, 1H), 7.69 (d, 1H, J ) 8.4
Hz), 7.24-7.15 (m, 6H), 7.09-7.02 (m, 2H), 6.93-6.86 (m, 2H),
6.22 (br s, 1H), 4.92 (m, 1H), 4.83-4.72 (m, 2H), 3.70 (s, 3H),
3.59 (m, 1H), 3.37 (dd, 1H, J ) 12.7, 5.1 Hz), 3.10 (dd, 1H, J
) 13.7, 5.2 Hz), 2.79 (dd, 1H, J ) 13.7, 9.7 Hz), 1.39 (s, 9H),
0.77 (br d, 3H, J ) 6.6 Hz); 13C NMR (100 MHz, CDCl3) δ
171.30, 167.49, 155.81, 153.57, 140.59, 135.89, 129.25, 128.73,
128.65, 128.51, 127.10, 126.78, 80.65, 68.17, 53.72, 52.55,
52.13, 47.75, 40.52, 37.59, 28.13, 22.72, 17.58; IR (KBr) νmax
3279, 3222, 3032, 2981, 1759, 1738, 1710, 1694, 1570, 1520,
1498, 1455, 1391, 1366, 1290, 1249, 1196, 1170, 1010, 751, 698
Da ta for 4a : colorless crystalline powder, mp 191-192 °C
(CHCl3-isopropyl ether); [R]24 -7.5° (c ) 0.56, MeOH); 1H
D
NMR (500 MHz, CDCl3) δ 8.28 (br s, 1H), 7.98 (br s, 1H), 7.23-
7.16 (m, 3H), 7.10-6.97 (m, 2H), 6.44 (br s, 1H), 5.63 (br m,
1H), 5.03 (br m, 1H), 4.82 (m, 1H), 3.72 (s, 3H), 3.19 (dd, 1H,
J ) 13.8, 5.4 Hz), 2.92 (m, 1H), 1.73 (br s, 3H), 1.64 (d, 3H, J

3270 J . Org. Chem., Vol. 67, No. 10, 2002
Hitotsuyanagi et al.
cm-1; FABMS m/z 522 [M + H]+. Anal. Calcd for C28H35N5O5:
Da ta for 4l: amorphous solid; [R]24D -1.7° (c ) 0.34, MeOH);
1H NMR (400 MHz, CDCl3) δ 8.47 (br s, 1H), 7.99 (br s, 1H),
7.23-7.16 (m, 3H), 7.13-7.06 (m, 2H), 6.40 (br s, 1H), 5.65 (q,
1H, J ) 6.9 Hz), 4.82 (m, 1H), 4.62-4.49 (m, 2H), 3.74 (s, 3H),
3.23 (dd, 1H, J ) 14.0, 5.5 Hz), 3.02 (dd, 1H, J ) 14.0, 8.8
Hz), 1.68 (d, 3H, J ) 6.9 Hz), 1.42 (s, 9H); 13C NMR (100 MHz,
CDCl3) δ 171.54, 168.36, 156.43, 151.22, 142.25, 135.93, 129.07,
128.56, 127.11, 80.61, 53.67, 53.45, 52.30, 37.68, 34.82, 28.34,
18.99; IR (film) νmax 3224, 2980, 1745, 1692, 1525, 1500, 1366,
1277, 1251, 1216, 1170, 861, 755, 701 cm-1; FABMS m/z 432
[M + H]+; HRFABMS calcd for C21H30N5O5 432.2247, found
432.2249.
C, 64.47; H, 6.76; N, 13.43. Found: C, 64.24; H, 6.80; N, 13.29.
Da ta for 4g: amorphous solid; [R]24 +1.6° (c ) 0.74,
D
MeOH); 1H NMR (500 MHz, CDCl3) δ 8.53 (s, 1H), 7.71 (br s,
1H), 7.29-7.15 (m, 6H), 7.02-6.94 (m, 4H), 5.55 (br s, 1H),
5.34 (br m, 1H), 4.54-4.43 (m, 2H), 3.72 (s, 3H), 3.32 (dd, 1H,
J ) 14.0, 5.5 Hz), 3.14 (dd, 1H, J ) 14.0, 9.8 Hz), 2.79 (dd,
1H, J ) 14.0, 9.8 Hz), 2.41 (dd, 1H, J ) 14.0, 5.6 Hz), 1.31 (d,
3H, J ) 7.2 Hz), 1.27 (s, 9H); 13C NMR (125 MHz, CDCl3) δ
172.31, 167.07, 155.84, 154.33, 141.12, 136.25, 135.31, 129.05,
128.92, 128.53, 127.39, 126.91, 80.51, 58.70, 52.31, 48.37,
45.83, 39.53, 38.63, 28.07, 17.49; IR (film) νmax 3317, 2981,
1746, 1679, 1549, 1523, 1454, 1367, 1253, 1217, 1168, 753, 700
cm-1; FABMS m/z 522 [M + H]+; HRFABMS calcd for
Da ta for 4m : colorless crystalline powder, mp 172 °C
(CHCl3-isopropyl ether); [R]25 -8.6° (c ) 1.01, MeOH); 1H
D
C
28H36N5O5 522.2716, found 522.2700.
NMR (400 MHz, CDCl3) δ 8.69 (s, 1H), 8.28 (br d, 1H, J ) 5.5
Hz), 7.23-7.10 (m, 3H), 6.95-6.85 (m, 2H), 6.16 (br m, 1H),
5.61 (dd, 1H, J ) 10.7, 4.5 Hz), 4.54 (m, 1H), 3.94-3.67 (m,
2H), 3.75 (s, 3H), 3.38 (dd, 1H, J ) 14.0, 4.5 Hz), 3.16 (dd, 1H,
J ) 14.0, 10.7 Hz), 1.37 (d, 3H, J ) 7.2 Hz), 1.36 (s, 9H); 13C
NMR (100 MHz, CDCl3) δ 172.50, 167.71, 156.18, 151.62,
142.46, 134.96, 128.83, 128.55, 127.20, 79.89, 58.76, 52.23,
48.31, 40.39, 34.11, 28.16, 17.35; IR (KBr) νmax 3422, 3209,
3144, 2984, 1740, 1684, 1570, 1511, 1278, 1163, 1061, 747, 702
cm-1; FABMS m/z 432 [M + H]+; HRFABMS calcd for
Da ta for 4h : colorless fine needles, mp 164-166 °C
1
(MeOH-H2O); [R]25 +10.0° (c ) 0.66, MeOH); H NMR (400
D
MHz, CDCl3) δ 8.05 (br s, 1H), 7.86 (br d, 1H, J ) 6.5 Hz),
7.27-7.12 (m, 8H), 6.97 (br s, 2H), 6.27 (br s, 1H), 5.27 (br s,
1H), 5.09 (m, 1H), 4.75 (m, 1H), 3.70 (s, 3H), 3.57 (br m, 1H),
3.41 (dd, 1H, J ) 13.1, 6.8 Hz), 3.11 (dd, 1H, J ) 13.7, 5.5
Hz), 2.88 (dd, 1H, J ) 13.7, 8.8 Hz), 2.27-2.11 (m, 4H), 1.99
(s, 3H), 1.37 (s, 9H); 13C NMR (100 MHz, CDCl3) δ 171.09,
166.80, 155.80, 153.73, 141.05, 135.99, 135.73, 129.29, 128.79,
128.66, 128.57, 127.15, 126.94, 80.75, 55.50, 53.81, 52.20,
47.09, 40.09, 37.64, 31.92, 29.49, 28.16, 15.35; IR (KBr) νmax
3231, 3028, 1734, 1708, 1696, 1523, 1282, 1254, 1170, 1015,
697 cm-1; FABMS m/z 582 [M + H]+. Anal. Calcd for
C
21H30N5O5 432.2247, found 432.2239.
Tr ia zolotetr a p ep tid e 5c. Compound 4c was added to 4
M HCl in dioxane (1.0 mL) at room temperature and stirred
for 1 h, and then the solvent was removed in vacuo. The
residue was dissolved in CHCl3 (0.5 mL), and N-Boc-D-alanine
(138 mg, 0.073 mmol) and HOBt (9.9 mg, 0.073 mmol) were
added to the solution. After dropwise addition of triethylamine
(10.2 µL, 0.073 mmol), EDC‚HCl (14.0 mg, 0.073 mmol) was
added to the solution, and the mixture was stirred at room
temperature for 1 day. Water (10 mL) was added to the
solution, and the mixture was extracted with CHCl3 (3 × 10
mL). The CHCl3 layer was washed with brine (5 mL), dried
over Na2SO4, and filtered, and the solvent was removed in
vacuo. The residue was chromatographed (MPLC, silica gel,
CHCl3/EtOAc/MeOH, 15/2/1) to provide 5c (27.2 mg, 86%) as
C
30H39N5O5S: C, 61.94; H, 6.76; N, 12.04. Found C, 61.84; H,
6.73; N, 11.97.
Data for 4i: colorless fine needles, mp 182-183 °C (MeOH-
H2O); [R]25 +23.3° (c ) 0.50, MeOH); 1H NMR (400 MHz,
D
CD3OD) δ 8.22 (br s, 1H), 7.29-7.18 (m, 3H), 7.10 (br d, 2H,
J ) 6.5 Hz), 6.83 (br d, 2H, J ) 8.5 Hz), 6.64 (d-like, 2H, J )
8.5 Hz), 5.03 (dd, 1H, J ) 10.1, 6.0 Hz), 4.88 (m, 1H), 4.56
(dd, 1H, J ) 8.7, 5.8 Hz), 3.69 (s, 3H), 3.33 (dd, 1H, 12.9, 6.0
Hz), 3.21 (dd, 1H, J ) 12.9, 10.1 Hz), 3.00 (dd, 1H, J ) 13.8,
5.8 Hz), 2.89 (dd, 1H, J ) 13.8, 8.7 Hz), 1.40 (s, 9H), 0.95 (br
d, 3H, J ) 5.7 Hz); 13C NMR (100 MHz, CD3OD) δ 173.17,
170.13, 157.53, 157.36, 156.14, 143.00, 137.66, 131.06, 130.62,
129.72, 128.40, 128.13, 116.39, 81.02, 55.87, 54.12, 52.71,
48.86, 41.44, 37.56, 28.69, 18.45; IR (KBr) νmax 3388, 3359,
3327, 2979, 1745, 1692, 1671, 1517, 1455, 1443, 1368, 1270,
1246, 1208, 1172, 704 cm-1; FABMS m/z 538 [M + H]+. Anal.
Calcd for C28H35N5O6: C, 62.55; H, 6.56; N, 13.03. Found C,
62.32; H, 6.61; N, 12.80.
an amorphous solid; [R]24 +18.8° (c ) 0.88, MeOH); 1H NMR
D
(400 MHz, CDCl3) δ 8.34 (s, 1H), 8.08 (d, 1H, J ) 7.7 Hz),
7.89 (d, 1H, J ) 8.0 Hz), 7.30-7.19 (m, 3H), 7.16 (d-like, 2H,
J ) 8.2 Hz), 5.44 (br s, 1H), 5.26 (m, 1H), 4.94-4.80 (m, 2H),
4.77 (m, 1H), 4.13 (m, 1H), 3.71 (s, 3H), 3.20 (dd, 1H, J ) 14.0,
5.5 Hz), 3.08 (dd, 1H, J ) 14.0, 8.3 Hz), 1.66 (d, 3H, J ) 7.0
Hz), 1.40 (s, 9H), 1.31 (d, 3H, J ) 7.1 Hz); 13C NMR (100 MHz,
CDCl3) δ 173.45, 171.62, 165.65, 155.41, 154.78, 144.63, 136.07,
129.04, 128.44, 126.93, 79.74, 54.03, 52.28, 50.30, 46.57, 39.73,
37.33, 28.19, 19.07, 18.28; IR (film) νmax 3286, 2981, 1744, 1691,
1523, 1454, 1367, 1249, 1218, 1168, 756, 701 cm-1; FABMS
m/z 503 [M + H]+; HRFABMS calcd for C24H35N6O6 503.2618,
found 503.2603.
Da ta for 4j: amorphous solid; [R]25D -7.0° (c ) 0.34, MeOH);
1H NMR (400 MHz, CDCl3) δ 8.45 (s, 1H), 7.85 (br s, 1H), 7.23-
7.11 (m, 3H), 7.08-6.94 (m, 2H), 6.19 (br s, 1H), 4.95 (br s,
1H), 4.69 (m, 1H), 4.52 (br t, 1H, J ) 8.4 Hz), 3.68 (s, 3H),
3.13 (dd, 1H, J ) 13.7, 6.1 Hz), 2.96 (dd, 1H, J ) 13.7, 8.1
Hz), 2.60 (m, 1H), 2.40 (m, 1H), 1.40, (s, 9H), 1.15 (d, 3H, J )
6.2 Hz), 1.10 (d, 3H, J ) 6.3 Hz), 0.86-0.74 (m, 6H); 13C
NMR (100 MHz, CDCl3) δ 171.17, 167.59, 156.46, 154.17,
141.84, 135.90, 128.90, 128.52, 127.02, 80.55, 63.66, 54.12,
52.23, 51.42, 37.81, 32.41, 31.81, 28.34, 20.37, 19.15, 19.05,
18.79; IR (film) νmax 3220, 2968, 1748, 1712, 1685, 1518,
1366, 1281, 1173, 1008, 757, 699 cm-1; FABMS m/z 502
[M + H]+; HRFABMS calcd for C26H40N5O5 502.3029, found
502.3036.
Tr ia zolotetr a p ep tid e 5f. As described for 5c, 4f provided
5f (81%) as colorless fine needles, mp 201-202 °C (CHCl3-
isopropyl ether); [R]26D +13.6° (c ) 0.59, MeOH); 1H NMR (400
MHz, CDCl3) δ 8.29 (br s, 1H), 8.03 (br s, 1H), 7.99 (s, 1H),
7.24-7.03 (m, 8H), 6.88-6.80 (m, 2H), 5.40 (br s, 1H), 5.14
(m, 1H), 4.96 (m, 1H), 4.68 (m, 1H), 4.24 (br m, 1H), 3.69 (s,
3H), 3.50 (dd, 1H, J ) 12.9, 10.1 Hz), 3.40 (dd, 1H, J ) 12.9,
6.0 Hz), 3.07 (dd, 1H, J ) 13.8, 5.5 Hz), 2.89 (dd, 1H, J ) 13.8,
8.5 Hz), 1.41 (s, 9H), 1.19 (d, 3H, J ) 7.0 Hz), 0.97 (d, 3H, J
) 6.9 Hz); 13C NMR (100 MHz, CDCl3) δ 173.94, 171.52,
167.68, 155.46, 153.01, 140.99, 136.08, 135.95, 129.33, 128.78,
128.49, 127.24, 126.78, 80.21, 53.97, 52.84, 52.35, 49.86, 46.67,
39.82, 37.34, 28.32, 18.49, 18.19; IR (KBr) νmax 3267, 2979,
1745, 1722, 1687, 1657, 1558, 1507, 1455, 1366, 1244, 1221,
1171, 702 cm-1; FABMS m/z 593 [M + H]+. Anal. Calcd for
Da ta for 4k : colorless crystalline powder, mp 207 °C
(CHCl3-isopropyl ether); [R]24 -7.9° (c ) 0.32, MeOH); 1H
D
NMR (400 MHz, CDCl3) δ 7.99 (s, 1H), 7.92 (br d, 1H, J ) 5.4
Hz), 7.25-7.18 (m, 3H), 7.00-6.92 (m, 2H), 6.34 (br s, 1H),
5.41 (m, 1H), 4.82 (m, 1H), 4.41 (br t, 1H, J ) 8.9 Hz), 3.72 (s,
3H), 3.15 (dd, 1H, J ) 13.7, 5.2 Hz), 2.83 (dd, 1H, J ) 13.7,
9.6 Hz), 2.63 (br m, 1H), 1.59 (d, 3H, J ) 6.9 Hz), 1.40 (s, 9H),
1.17 (d, 3H, J ) 6.5 Hz), 0.77 (d, 3H, J ) 6.6 Hz); 13C NMR
(100 MHz, CDCl3) δ 171.36, 167.55, 156.42, 154.06, 140.83,
135.97, 128.86, 128.62, 126.93, 80.58, 53.87, 52.71, 52.26,
51.72, 37.80, 32.07, 28.24, 19.66, 19.58, 18.97; IR (KBr) νmax
3239, 2974, 1740, 1714, 1695, 1536, 1519, 1365, 1280, 1247,
1227, 1199, 1169, 1011, 754, 701 cm-1; FABMS m/z 474 [M +
H]+. Anal. Calcd for C24H35N5O5: C, 60.87; H, 7.45; N, 14.79.
Found: C, 60.69; H, 7.27; N, 14.54.
C
31H40N6O6: C, 62.82; H, 6.80; N, 14.18. Found: C, 63.03; H,
6.85; N, 14.04. Crystal data for 5f: C31H40N6O6, M ) 592.70,
0.4 × 0.2 × 0.1 mm3, monoclinic, P21, a ) 13.992 (3), b ) 10.865
(4), c ) 10.575 (2) Å, â ) 90.55 (2)°, V ) 1607.6 (7) Å3, T )
298 K, Z ) 2, µ(Cu KR) ) 6.705 mm-1, 3507 reflections
measured, 3067 unique reflections (Rint ) 0.027), R ) 0.048,
Rw ) 0.072. The structure was solved by direct methods and
expanded using Fourier techniques.

A cis Amide Bond Surrogate
J . Org. Chem., Vol. 67, No. 10, 2002 3271
Tr ia zolotetr a p ep tid e 6g. As described for 5c, 4g provided
7.48 (d, 1H, J ) 9.2 Hz), 7.24 (dd, 1H, J ) 8.3, 2.1 Hz), 7.21
(dd, 1H, J ) 8.3, 2.1 Hz), 7.10 (d-like, 2H, J ) 8.6 Hz), 7.03
(dd, 1H, J ) 8.6, 2.1 Hz), 6.82 (d-like, 2H, J ) 8.6 Hz), 6.74 (d,
1H, J ) 8.2 Hz), 6.62 (dd, 1H, J ) 8.2, 1.9 Hz), 6.16 (d, 1H, J
) 6.8 Hz), 5.99 (dd, 1H, J ) 12.2, 4.4 Hz), 5.77 (q, 1H, J ) 6.6
Hz), 5.30-5.23 (m, 2H), 4.63 (d, 1H, J ) 1.9 Hz), 4.50 (m, 1H),
3.91 (s, 3H), 3.76 (s, 3H), 3.71 (dd, 1H, J ) 13.8, 7.6 Hz), 3.39-
3.31 (m, 2H), 3.07-3.00 (m, 3H), 2.99 (s, 3H), 2.91 (dd, 1H, J
) 14.4, 3.9 Hz), 2.81 (m, 1H), 2.75 (s, 3H), 2.33 (s, 3H), 1.42
(d, 3H, J ) 6.6 Hz), 1.31 (d, 3H, J ) 6.7 Hz), 0.99 (d, 3H, J )
6.8 Hz); 13C NMR (125 MHz, 315 K, CDCl3, major conformers)
δ 172.94, 172.86, 168.44, 167.97, 167.94, 159.25, 158.23,
152.24, 149.79, 146.84, 141.25, 133.84, 131.95, 131.15, 130.51,
130.42, 128.21, 127.44, 124.01, 121.83, 119.62, 114.73, 112.48,
68.79, 56.30, 55.37, 54.34, 53.74, 51.39, 49.23, 43.43, 41.12,
38.01, 34.70, 32.12, 29.31, 29.22, 20.23, 20.10, 19.07; IR (KBr)
νmax 3377, 3308, 2979, 2935, 1656, 1630, 1515, 1499, 1443,
1412, 1267, 1251, 1215, 1129, 1091 cm-1; FABMS m/z 795 [M
+ H]+; HRFABMS calcd for C42H51N8O8 795.3830, found
795.3814.
6g (82%) by using N-Boc-glycine as an amorphous solid; [R]24
D
1
-14.6° (c ) 0.77, MeOH); H NMR (400 MHz, CDCl3) δ 8.58
(s, 1H), 7.99 (br s, 1H), 7.93 (br d, 1H, J ) 6.1 Hz), 7.32-7.14
(m, 6H), 7.01 (d-like, 2H, J ) 7.0 Hz), 6.96 (d-like, 2H, J ) 6.8
Hz), 5.44 (br s, 1H), 5.37 (m, 1H), 4.73 (m, 1H), 4.42 (m, 1H),
3.71 (s, 3H), 3.69 (m, 1H), 3.57 (dd, 1H, J ) 17.2, 5.1 Hz), 3.34
(dd, 1H, J ) 13.9, 5.3 Hz), 3.26 (dd, 1H, J ) 13.9, 9.7 Hz),
2.85 (dd, 1H, J ) 13.9, 9.9 Hz), 2.62 (m, 1H), 1.36 (s, 9H), 1.33
(d, 3H, J ) 7.2 Hz); 13C NMR (100 MHz, CDCl3) δ 172.51,
170.73, 167.05, 155.88, 153.99, 141.45, 136.30, 135.34, 129.06,
128.96, 128.55, 127.48, 127.00, 79.89, 58.99, 52.36, 48.57,
45.08, 43.39, 39.63, 38.21, 28.22, 17.11; IR (film) νmax 3286,
2980, 1745, 1685, 1540, 1499, 1455, 1367, 1281, 1247, 1217,
1171, 754, 701 cm-1; FABMS m/z 579 [M + H]+; HRFABMS
calcd for C30H39N6O6 579.2931, found 579.2917.
Tr ia zole An a logu e of RA-VII 10. To a suspension of
thioamide 8 (40.3 mg, 0.0512 mmol) and formic hydrazide (15.4
mg, 0.256 mmol) in MeCN (0.25 mL) was added mercury(II)
acetate (24.5 mg, 0.0769 mmol), and the mixture was stirred
at room temperature for 72 h. Water (10 mL) was added to
the mixture, and the mixture was extracted with CHCl3 (2 ×
10 mL). The CHCl3 extract was washed with brine (5 mL),
dried over Na2SO4, and filtered, and the solvent was removed
in vacuo. The residue was chromatographed (MPLC, silica gel,
CHCl3/EtOAc/MeOH, 20:2:1) to provide triazole 10 (19.4 mg,
Su p p or tin g In for m a tion Ava ila ble: 1H NMR spectra of
1 (R1 ) H), precursors of 1, 3a -m , 4a -m , 5c,f, 6g, and 10,
and X-ray data and an ORTEP diagram of 5f. This ma-
terial is available free of charge via the Internet at http://
pubs.acs.org.
48%) as a crystalline powder, mp > 300 °C (MeOH); [R]23
D
1
-124° (c ) 0.16, CHCl3); H NMR (500 MHz, 315 K, CDCl3,
major conformer) δ 8.13 (s), 7.51 (dd, 1H, J ) 8.6, 2.1 Hz),
J O010904I