Application of DEPBT for synthesis of N-protected peptide alcohols and its derivatives

Article abstract of DOI:10.1081/SCC-120002133

A series of N-protected peptide alcohols and one N-glycopeptide derivative were synthesized using DEPBT. We showed that the carboxyl group selectively reacted with amino group of the amino component in the presence of unprotected hydroxy groups.

Full text of DOI:10.1081/SCC-120002133

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APPLICATION OF DEPBT FOR SYNTHESIS OF N-
PROTECTED PEPTIDE ALCOHOLS AND ITS DERIVATIVES
Ping Liu a , Bin-yuan Sun a , Xiao-hua Chen a , Gui-ling Tian a & Yun-hua Ye a
a Department of Chemistry , Key Laboratory of Bioorganic Chemistry and Molecular
Engineering , Peking University , Beijing, 100871, China
Published online: 16 Aug 2006.
To cite this article: Ping Liu , Bin-yuan Sun , Xiao-hua Chen , Gui-ling Tian & Yun-hua Ye (2002) APPLICATION OF DEPBT
FOR SYNTHESIS OF N-PROTECTED PEPTIDE ALCOHOLS AND ITS DERIVATIVES, Synthetic Communications: An International
Journal for Rapid Communication of Synthetic Organic Chemistry, 32:3, 473-480
To link to this article: http://dx.doi.org/10.1081/SCC-120002133
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SYNTHETIC COMMUNICATIONS, 32(3), 473–480 (2002)
APPLICATION OF DEPBT FOR
SYNTHESIS OF N-PROTECTED PEPTIDE
ALCOHOLS AND ITS DERIVATIVES
Ping Liu, Bin-yuan Sun, Xiao-hua Chen,
Gui-ling Tian, andYun-hua Ye *
Key Laboratory of Bioorganic Chemistry and
Molecular Engineering, Department of Chemistry,
Peking University, Beijing 100871, China
ABSTRACT
A series of N-protected peptide alcohols and one N-glycopep-
tide derivative were synthesized using DEPBT. We showed
that the carboxyl group selectively reacted with amino
group of the amino component in the presence of unprotected
hydroxy groups.
Key Words: DEPBT; Coupling reagent; Peptide alcohol;
N-Glycopeptide
3-(Diethoxyphosphoryloxy)-(1,2,3)-benzotriazin-4(3H)-one(DEPBT)
is an efficient coupling reagent for peptide syntheses which was developed by
our group.1 During the coupling reaction, side reactions and racemization
are minimal.2 Moreover, the hydroxy group of amino component does not
*Corresponding author. Fax: 86-10-62751708; E-mail: yhye@pku.edu.cn
473
Copyright & 2002 by Marcel Dekker, Inc.
www.dekker.com

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LIU ET AL.
need to be protected. Thus DEPBT is useful for the synthesis of peptide
alcohols, which have attracted much attention not only as ligands3 but also
as enzyme inhibitors.4 The hydroxy group of amino alcohols has to be
protected when DCC or EDCI are used as coupling reagents for the syn-
thesis of peptide alcohols. We previously reported some of N-protected
peptide alcohols prepared by DEPBT.5
In this paper, we reported the use of DEPBT in the synthesis of a series
of peptide alcohols and a N-glycopeptide derivative from N-protected
amino acids and different amino components with one or more unprotected
hydroxy groups (scheme). The results showed that using DEPBT as coup-
ling reagent, the carboxyl group of carboxyl component selectively reacted
Scheme. Synthesis of N-protected peptide alcohols and its derivatives using
DEPBT.
with the amino group of amino component to form an amide rather than
an ester (table). Even in the case of p-amino-phenol with an active hydroxy
group, no ester was formed. Nine N-protected peptide alcohols were syn-
thesized using DEPBT (table). Two of them, compounds, 7 and 9, are
the fragments of the bioactive peptide analog, Octreotide.6 We also
showed that our coupling reagent DEPBT was useful for the synthesis of
N-glycopeptides. Typically, the carboxyl group is activated by pentafluoro-
phenol for the reaction with the amino component with unprotected
hydroxy groups (e.g. glucosamine) when DCC is used as coupling reagent.7
Pentafluorophenol activation becomes unnecessary when DCC is replaced
by DEPBT. Furthermore, DEPBT is suitable for coupling reactions in
anhydrous solvents (e.g. anhydrous THF, DMF, CH2Cl2), in two-phase
solvent systems (e.g. CH2Cl2/H2O) and water–organic mixed solvents (e.g.
THF/H2O, DMF/H2O). The yield in the two-phase solvent systems was
comparable to that in anhydrous solvents. The yield in water–organic
mixed solvents was slightly lower than in anhydrous solvents. This is
because DEPBT and the active ester formed may decompose by water in
base media. In addition, the yield also depended on the amino component.

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SYNTHESIS OF N-PROTECTED PEPTIDE ALCOHOLS
475
Table. The Yields and Methods of Synthesis of Peptide Alcohols and Its
Derivatives
As for compound 10, the yield was lower than for other amino alcohols
probably because glucosamine is not stable under the reaction conditions.
In conclusion, DEPBT is an efficient coupling reagent for amide for-
mation from carboxyl and amino components with one or more unprotected
hydroxy groups in the latter, especially for the synthesis of N-protected
peptide alcohols and N-glycopeptides.

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LIU ET AL.
EXPERIMENTAL
The melting points were determined with Yanaco micromelting point
apparatus and were uncorrected. Mass spectra were recorded on VG-ZAB-
1
HS spectrometer. H NMR was recorded on Bruker arx-400, 200 and dmx-
300. Elemental analysis was performed by Hezaeus CHN-Rapid elemental
analyzer. Optical rotation was measured by Perkin-Elmer 241 or 241 MC
polarimeter.
THF was redistilled form Na/benzophenone. CH2Cl2 was dried
by anhydrous K2CO3 and redistilled. DL-2-amino-butanol, DL-1-amino-2-
propanol, DMF and pyridine (C5H5N) were redistilled and p-amino
phenol was recrystallized prior to use. Other reagents, such as glucosamine
hydrochloride,i.e.D-2-amino-glucosehydrochloride,(½aŠ ¼ þ71ꢀÀþ72:6ꢀ),
20
D
(1s, 2s)-(þ)-2-amino-1-phenyl-1,3-propanedioletc.,werecommercialreagents
and used without further purification.
General Procedure for Preparation of N-ProtectedPeptide
Alcohol and N-Glycopeptide Derivatives
Method A
To a mixture of 0.5 mmol of the carboxyl component, 0.55 mmol
DEPBT, 5 mL THF (CH2Cl2 or DMF) and 0.55 mmol Et3N (0.077 mL),
was added 0.5 mmol of the amino component. The pH of solution was
adjusted to 8–9 by adding Et3N and the mixture stirred at room temperature
for about 10 h. The reaction was followed by TLC. At the end of the reac-
tion, the solvent was evaporated under vaccum and the oily residue dissolved
in 30 mL of ethyl acetate. The solution was successively washed with 1 M
HCl, H2O, 5% NaCO3, H2O and saturated NaCl solution. The organic
layer was dried over anhydrous MgSO4. The solvent was removed and the
crude product recyrstallized from a suitable solvent (ethyl acetate/petroleum
or chloroform/petroleum) or purified by silica gel chromatograph
(CHCl3 : MeOH ¼ 9 : 1) to afford pure product.
Method B
To a mixture of 0.5 mmol of the carboxy component, 0.55 mmol
DEPBT and 4 mL CH2Cl2, was added 0.55 mmol Et3N (0.077 mL). After
stirring for 0.5 h, 0.5 mmol of the amino component dissolved in 1 mL of
distilled water was added. The pH of solution was adjusted to 8–9 by adding

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SYNTHESIS OF N-PROTECTED PEPTIDE ALCOHOLS
477
Et3N. The solution was stirred at room temperature for about 12 h and the
reaction followed by TLC. The product was isolated and purified as
described above for Method A.
Method C
To a mixture of 0.5 mmol of the carboxyl component, 0.55 mmol
DEPBT and 2 mL THF, was added 0.55 mmol Et3N (0.077 mL). The pH
of solution was adjusted to 8–9 by adding Et3N and the solution was stirred
at room temperature for about 0.5 h, then 0.5 mmol of the amino compon-
ent dissolved in a mixture of 2.1 mL THF and 0.7 mL distilled water was
quickly added under rigorously stirring. The mixture was stirred at room
temperature for about 7 h and the reaction followed by TLC. The product
was isolated and purified as described above for Method A. As for amino
component glucosamine hydrochloride, Et3N was used to neutralize hydro-
chloride before the solution of glucosamine hydrochloride was added to
react with N-protected amino acid. The corresponding product was immedi-
ately precipitated from the reaction mixture after the amino component was
added. The precipitate was filtered at the end of reaction and successively
washed with a little cold water and methanol, then the crude product recrys-
tallized from water or methanol to give pure product.
Compound1
m.p. 120–121.5ꢀC; ½aŠ ¼ À19:6ꢀ ðc ¼ 1, MeOHÞ; FAB-MS: m/z 295
20
D
(M þ H)þ; elemental analysis for C15H22O4N2 (%): found (calcd.) C 61.26
(61.22); H 7.51 (7.48); N 9.72 (9.52).
1H NMR (400 MHz, CDCl3) d: 0.91 (q, 3H, CH3), 1.39 (d, J ¼ 7.0 Hz,
3H, CH3), 1.47 (m, 1H, CH2), 1.57 (m, 1H, CH2), 2.21 (s, 1H, OH), 3.54 (m,
1H, CH), 3.67 (m, 1H, CH), 3.82 (m, 1H, CH2OH), 4.20 (m, 1H, CH2OH),
5.11 (d, J ¼ 4.0 Hz, 2H, CH2O), 5.32 (s, 1H, CONH), 6.18 (s, 1H, CONH),
7.32–7.38 (m, 5H, Ar-H) ppm.
Compound2
m.p. 113.5–115.5ꢀC; ½aŠ ¼ À4:9ꢀ ðc ¼ 1, MeOHÞ; FAB-MS: m/z 357
20
D
(M þ H)þ; elemental analysis for C20H24O4N2 (%): found (calcd.) C 67.83
(67.42); H 6.81 (6.74); N 7.96 (7.86).

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LIU ET AL.
1H NMR (200 MHz, CDCl3) d: 1.07 (d, J ¼ 6.4 Hz, 3H, CH3), 1.93 (s,
1H, OH), 3.01 (m, 3H, CH2), 3.35 (m, 1H, CH2), 3.72 (m, 1H, CH), 4.37 (q,
1H, CH), 5.07 (s, 2H, CH2O), 5.40 (s, 1H, CONH), 6.12 (d, 1H, CONH),
7.12–7.33 (m, 10H, Ar-H) ppm.
Compound3
m.p. 140.5–142.5ꢀC; ½aŠ ¼ þ5:9ꢀ ðc ¼ 1, MeOHÞ; FAB-MS: m/z 357
20
D
(M þ H)þ; elemental analysis for C20H24O4N2 (%): found (calcd.) C 67.79
(67.42); H 6.67 (6.74); N 7.92 (7.86).
1H NMR (200 MHz, CDCl3) d: 0.93 (d, J ¼ 6.8 Hz, CH3), 2.04 (s, 1H,
OH), 3.05 (m, 2H, CH2), 3.39 (m, 1H, CH), 3.57 (m, 1H, CH), 3.93 (m, 1H,
CH2OH), 4.32 (m, 1H, CH2OH), 5.06 (s, 2H, CH2O), 5.47 (s, 1H, CONH),
5.78 (s, 1H, CONH), 7.17–7.33 (m, 10H, Ar-H) ppm.
Compound4
m.p. 180–182.5ꢀC; ½aŠ ¼ À43:7ꢀ ðc ¼ 0:5, MeOHÞ; FAB-MS: m/z 315
20
D
(M þ H)þ; elemental analysis for C17H18O4N2 (%): found (calcd.) C 64.67
(64.97); H 5.63 (5.73); N 8.76 (8.92).
1H NMR (200 MHz, DMSO-d6) d: 1.27 (d, J ¼ 7.0 Hz, 3H, CH3), 4.14
(m, 1H, CH), 5.02 (s, 2H, CH2O), 6.68 (d, 2H, Ar-H), 7.35–7.56 (m, 8H, Ar-
H, CONH), 9.19 (1H, s, CONH), 9.72 (1H, s, OH) ppm.
Compound5
m.p. 51.0–53.0ꢀC; ½aŠ ¼ À2:8ꢀ ðc ¼ 1, MeOHÞ; FAB-MS: m/z 373
20
D
(M þ H)þ; elemental analysis for C20H24O5N2ꢁH2O (%): found (calcd.) C
61.59 (61.53); H 6.59 (6.66); N 6.91 (7.18).
1H NMR (200 MHz, CDCl3) d: 1.18 (d, J ¼ 6.8 Hz, 3H, CH3),
2.75–4.05 (br, 2H, OH), 3.80 (m, 2H, CH), 4.10 (m, 3H, CH2, CH), 5.06
(s, 2H, CH2O), 5.44 (s, 1H, CONH), 6.75 (s, 1H, CONH), 7.26–7.32 (m,
10H, Ar-H) ppm.
Compound6
m.p. 126.0–129.0ꢀC; ½aŠ ¼ À14:4ꢀ ðc ¼ 0:97, DMFÞ; FAB-MS: m/z
20
D
493 (M þ H)þ; elemental analysis for C28H32O5N2 (%): found (calcd.) C
68.41 (68.28); H 6.47 (6.55); N 5.67 (5.69).

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SYNTHESIS OF N-PROTECTED PEPTIDE ALCOHOLS
479
1H NMR (CDCl3, 400 Hz) d: 1.07 (d, J ¼ 6.8 Hz, 3H, CH3); 1.28–3.15
(br, 2-OH); 2.97 (q, 1H, CH2); 3.02 (m, 1H, CH2); 3.65 (m, 3H, CH); 4.05
(m, 1H, CH2OH); 4.34 (q, 1H, CH2OH); 5.03 (s, 2H, CH2O); 5.08 (s, 2H,
CH2O); 5.39 (d, J ¼ 7.3 Hz, 1H, CONH); 6.38 (d, J ¼ 7.9 Hz, 1H, CONH);
6.90 (d, J ¼ 8.6 Hz, 2H, Ar-H); 7.12 (d, J ¼ 8.4 Hz, 2H, Ar-H); 7.26–7.42 (m,
10H, Ar-H) ppm.
Compound7
m.p. 112.0–115.0ꢀC; ½aŠ ¼ À10:9ꢀ ðc ¼ 0:99, DMFÞ; FAB-MS: m/z
20
D
502 (M þ H)þ; elemental analysis for C15H31O6N3S (%): found (calcd.) C
59.56 (59.89); H 6.15 (6.18); N 8.15 (8.38).
1H NMR (300 MHz, DMSO-d6) d: 0.98 (d, J ¼ 6.3 Hz, 3H, CH3); 1.84
(s, 3H, CH3); 2.67 (m, 1H, CH2S); 2.88 (m, 1H, CH2S); 3.27–3.35 (m, 3H,
2OH, CH), 3.42 (m, 1H, CH); 3.60 (m, 1H, CH); 3.86 (m, 1H, CH2OH);
4.12–4.35 (m, 6H, CH2O, CH2OH, CH2N, CH); 7.29–7.35 (m, 3H, 2Ar-H,
CONH); 7.40 (d, J ¼ 7.4 Hz, 2H, Ar-H); 7.63 (d, J ¼ 8.6 Hz, 1H, CONH);
7.72 (d, J ¼ 7.4 Hz, 2H, Ar-H); 7.88 (d, J ¼ 7.4 Hz, 2H, Ar-H); 8.52 (t, 1H,
CONH) ppm.
Compound8
m.p. 147.0–149.0ꢀC; ½aŠ ¼ À11:8ꢀ ðc ¼ 1, DMFÞ; FAB-MS: m/z 479
20
D
(M þ H)þ; elemental analysis for C27H30O6N2 (%): found (calcd.) C 67.60
(67.77); H 6.34 (6.32); N 5.78 (5.85).
1H NMR (300 MHz, DMSO-d6) d: 2.66 (t, 1H, CH2); 2.91 (dd,
J1 ¼ 3.6 Hz, J2 ¼ 13.5 Hz, 1H, CH2); 3.37–3.43 (m, 5H, 2OH, 2CH,
CH2OH); 3.70 (m, 1H, CH2OH); 4.21 (m, 1H, CH2OH); 4.66 (m, 1H,
CH2OH); 4.93 (s, 2H, CH2O); 5.04 (s, 2H, CH2O); 6.89 (d, J ¼ 8.1 Hz,
2H, Ar-H); 7.18–7.44 (m, 13H, 12Ar-H, CONH); 7.69 (d, J ¼ 8.0 Hz, 1H,
CONH) ppm.
Compound9
m.p. 142.0–144.0ꢀC; ½aŠ ¼ À10:5ꢀ ðc ¼ 1:05, DMFÞ; FAB-MS: m/z
20
D
831 (M þ H)þ; elemental analysis for C40H58O11N6S (%): found (calcd.) C
57.42 (57.85); H 7.21 (6.98); N 10.02 (10.11).

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LIU ET AL.
Compound10
m.p. 193–196ꢀC (partly decomposed); ½aŠ ¼ þ62:2ꢀ ðc ¼ 1, MeOHÞ;
20
D
FAB-MS: m/z 385 (M þ H)þ; elemental analysis for C17H24O8N2 (%):
found (calcd.) C 53.12 (53.12); H 6.32 (6.15); N 7.49 (7.29).
1H NMR (400 MHz, DMSO-d6) d: 1.20 (d, J ¼ 7.1 Hz, 3H, CH3), 3.11
(m, 1H, CH2), 3.35 (s, 4OH), 3.35–3.69 (m, 5H, 3CH, CH2OH), 4.12 (dd,
J ¼ 7.5 Hz, 1H, CH), 4.48 (d, J ¼ 7.5 Hz, 0.18H, CH1 (b form)), 4.92
(d, J ¼ 3.3 Hz, 0.82H, CH1 (a form)), 5.01 (d, J ¼ 6.4 Hz, 2H, CH2O), 6.48
(d, J ¼ 3.9 Hz, CONH), 7.26–7.39 (m, 5H, Ar-H), 7.56 (d, J ¼ 8.1 Hz, 0.82H,
CONH (a form)), 7.74 (d, J ¼ 7.9 Hz, 0.18H, CONH (b form)) ppm.
ACKNOWLEDGMENT
This work was supported by National Natural Science Foundation of
China (No. 29872002)
REFERENCES
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5. Sun, B.-Y.; Tian, G.-L.; Wang, W.; Jin, N.; Ye, Y.-H. Acta scientiarum
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Received in the USA March 19, 2001

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