Improved procedure for the synthesis of DAMGO

Article abstract of DOI:10.1080/00397910701411044

A short and straightforward synthesis of DAMGO is described. Copyright Taylor & Francis Group, LLC.

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Improved Procedure for the Synthesis of
DAMGO
P. Anantha Reddy a , Anita H. Lewin a & F. Ivy Carroll a
a Organic and Medicinal Chemistry , Science and Engineering Group, RTI
International , Research Triangle Park, North Cardina, USA
Published online: 11 Jul 2007.
To cite this article: P. Anantha Reddy , Anita H. Lewin & F. Ivy Carroll (2007) Improved Procedure for the
Synthesis of DAMGO, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 37:14, 2345-2348, DOI: 10.1080/00397910701411044
To link to this article: http://dx.doi.org/10.1080/00397910701411044
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Synthetic Communicationsw, 37: 2345–2348, 2007
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910701411044
Improved Procedure for the Synthesis
of DAMGO
P. Anantha Reddy, Anita H. Lewin, and F. Ivy Carroll
Organic and Medicinal Chemistry, Science and Engineering Group,
RTI International, Research Triangle Park, North Cardina, USA
Abstract: A short and straightforward synthesis of DAMGO is described.
Keywords: DAMGO trifluoroacetate, m-opioid receptor ligand, peptide synthesis
As a selective opioid m-receptor-specific ligand, DAMGO (Tyr-D-Ala-
Gly-Na-Me-Phe-Gly-ol) is a widely used peptide in investigations of m-
receptor-mediated pharmacology.[1,2] As part of our program on opioid
peptides, we had developed a solution methodology suitable to the preparation
of gram amounts of highly pure DAMGO. The synthetic scheme consisted of a
(3 þ 1 þ 1) approach in which synthetic Boc-Tyr-D-Ala-Gly-Na-Me-Phe-OH
(1, R ¼ H) (Chart 1) was prepared starting from Boc-Na-Me-Phe-OH in three
steps to give TFA†DAMGO in 6% overall yield. We now report our new
synthetic methodology for introduction of the Gly-ol residue. Specifically,
we have determined that heating the tetrapeptide, Boc-Tyr-D-Ala-Gly-Na-
Me-Phe-OR (1, R ¼ Me), in excess ethanolamine leads to amidation of the
Na-methylpenylalanine methyl ester residue cleanly and quantitatively.
Thus, the protected tetrapeptide, Boc-Tyr-D-Ala-Gly-Na-Me-Phe-OR (1,
R ¼ Me) was prepared in three steps (68% overall yield), following the pre-
viously described methodology. Condensation with ethanolamine
Received in the USA December 8, 2006
Address correspondence to P. Anantha Reddy, Organic and Medicinal Chemistry,
Science and Engineering Group, RTI International, P.O. Box 12194, Research
Triangle Park, North Cardina 27709-2194, USA. E-mail: ananth@rti.org
2345

2346
P. A. Reddy, A. H. Lewin, and F. I. Carroll
Chart 1.
quantitatively afforded the protected pentapeptide, Boc-Tyr-D-Ala-Gly-Na-
Me-Phe-Gly-ol (2). Deprotection of the Boc group using 50% TFA in CH2Cl2
afforded DAMGO trifluoroacetate (3) in 58% overall yield after purification
by preparative high performance liquid chromatography (HPLC). The signifi-
cantly higher yield resulted primarily from the improved yield obtained in the
preparation of precursor tetrapeptide Boc-Tyr-D-Ala-Gly-Na-Me-Phe-OR
(1, R ¼ Me) (68%) vs. the precursor Boc-Tyr-D-Ala-Gly-Na-Me-Phe-OR (1,
R ¼ Bn) (25%) and in the introduction of the fifth Gly-ol residue (85% vs. 24%).
In summary, we have developed a racemization-free synthetic protocol
that is relatively short and affords the product in high overall yield. We
have prepared multigram quantities of highly pure DAMGO suitable for bio-
physical and pharmacological studies utilizing this procedure.
EXPERIMENTAL
1H NMR spectra were determined on a Bruker 300 and 500 spectrometer using
tetramethylsilane as an internal standard. Mass spectral data were obtained
using a Finnegan LCQ electrospray mass spectrometer in positive ion mode
at atmospheric pressure. Optical rotation was measured at the sodium D line
using a Rudolph Research Autopol III Polarimeter. Thin-layer chromato-
graphy (TLC) was carried out on precoated plates (silica gel 60 F254
,
250 mm; Merck Darmstadt, Germany), and the following solvent systems
were used (all v/v): EtOAc/EtOH (95:5); CHCl3/MeOH/HOAc (80:18:2);
n-BuOH/HOAc/H2O/pyridine (15:3:12:10). HPLC was performed utilizing
two Dynamax solvent-delivery system model SD-300 pumps and a model
UV-D II Dynamax absorbance detector. Elemental analysis was carried out
by Atlantic Microlabs, Inc.
Boc-Tyr-D-Ala-Gly-Na-Me-Phe-OR (1, R 5 Me)
The synthesis of this intermediate was analogous to that reported for the prep-
aration of Boc-Tyr-D-Ala-Gly-Na -Me-Phe-OR (1, R ¼ Bn).[3] Yield: 68%.
TLC single spot, Rf 0.7 [EtOAc/EtOH (95:5)]; 1H NMR (DMSO-d6):
d 1.22 (3H, d, Ala bCH3), 1.31 [9H,s, C(CH3)3], 2.71–2.78 (2H, m,
Tyr bCH2), 2.76 (3H, s, Phe NaCH3), 3.04–3.16 (2H, m, Phe bCH2), 3.63

Improved Procedure for the Synthesis of DAMGO
2347
(3H, s, OCH3), 3.68–3.71 (2H, m, Gly aCH2), 4.1 (1H, m, Ala aCH), 4.3
(1H, m, Tyr aCH), 4.95 (1H, m, Phe aCH), 6.63 (2H, d, Tyr ArH), 6.83
(1H, d, NH), 7.02 (2H, d, Tyr ArH), 7.19–7.29 (5H, m, ArH), 8.05 (2H, m,
2 ꢀ NH), and 9.14 (1H, s, Tyr OH); ESI MS, m/z 485.4 (M-Boc þ H),
607.8 (M þ Na).
Boc-Tyr-D-Ala-Gly-Na-Me-Phe-Gly-ol (2)
A mixture of Boc-Tyr-D-Ala-Gly-Na-Me-Phe-OR (1, R ¼ Me) (4.42 g,
7.2 mmol) and ethnolamine (20 mL) was heated at 608C (oil bath)
overnight. TLC [CHCl3/MeOH/HOAc (80:18:2)] analysis showed
complete disappearance of the starting material. The excess ethanolamine
was evaporated under reduced pressure, and the residue was dissolved in
methanol (25 mL). Upon addition of hexanes, a white precipitate formed.
The precipitate was collected by filtration and washed with hexanes.
This solid was vacuum dried to obtain the title compound as a white
solid (4.65 g, 100%): TLC single spot, Rf 0.60 [EtOAc/MeOH/
HOAc (80:18:2)]; 1H NMR (MeOH-d4) d 1.15 (3H, dd, AlabCH3), 1.3
[9H, s, C(CH3)3], 2.8 (3H, s, Phe NaCH3), 2.85–3.0 (2H, m, PhebCH2),
3.43–3.51 (2H, m, GlyaCH2), 3.9 (1H, br s, Ala aCH), 4.0–4.15
(1H, m, Tyr aCH), 4.3–4.45 (1H, m, PheaCH), 6.65 (2H, d, Tyr ArH),
6.95 (2H, d, Tyr ArH), 7.1–7.2 (5H, m, PheArH); ESI MS m/z 614.7
(M þ H), m/z 514.8 [M-Boc þ H)], 637.2 (M þ Na).
TFA † Tyr-D-Ala-Gly-Na-Me-Phe-Gly-ol (3)
To a chilled solution of Boc-Tyr-D-Ala-Gly-Na-Me-Phe-Gly-ol (2) (4.0 g,
6.52 mmol) in CH2Cl2 (60 mL), TFA (40 mL). was added. The resultant
mixture was stirred 1 h at room temperature. After evaporation of the
volatiles, the residue was triturated with Et2O (100 mL), causing formation
of a white precipitate. The solid was collected by filtration, washed with
ether (2 ꢀ 50 mL) and vacuum dried, affording the title compound as a
white powder (3.93 g, 96%). The crude peptide was purified by preparative
reversed phase HPLC on a Dynamax C18 column (8 m) (41.4 mm ꢀ 25 cm)
using a gradient 10%B ! 60%B over 30 min at 15-mL/min flow rate, with
detection at 215 nm, solvent A being 0.1% TFA/H2O, and solvent B being
0.1% TFA/CH3CN. The peptide eluting at 10.2 min was collected and lyophi-
lized to obtain a fluffy white sold in 85% yield. TLC, single spot, Rf, 0.75, [n-
BuOH/HOAc/H2O/pyridine (15:3:12:10); HPLC single peak (99%) Rt
10.71 min, on a Dynamax column (5 m) (4.6 mm ꢀ 25 cm) using a gradient
10%B ! 60%B over 25 min at 1.0 mL/min, with UV detection at 215 nm,
solvent A being 0.10% TFA/H2O, and solvent B being 0.10%TFA/
CH3CN. ESI MS m/z 514.8 (M þ H); [a]2D5 : þ26.85 (c. 0.5 MeOH). Anal.

2348
P. A. Reddy, A. H. Lewin, and F. I. Carroll
.
.
calcd. for C28H36F3N5O8 0.33 CF3CO2H 1.1 H2O : C, 50.29; H, 5.62, F,
11.06, N, 10.22. Found: C, 50.26; H, 5.64; F, 10.06; N, 10.18.
ACKNOWLEDGMENT
This work was supported by the National Institute on Drug Abuse, Contract
No. NO1DA-3-7736.
REFERENCES
1. Handa, B. K.; Lane, A. C.; Lord, J. A. H.; Morgan, B. A.; Rance, M. J.; Smith, C. F. C.
Eur. J. Pharmacol. 1981, 70, 531.
2. Kosterlitz, H. W.; Paterson, S. J. Br. J. Pharmacol. 1981, 73, 299.
3. Reddy, P. A.; Hayes, J. P.; Lewin, A. H.; Brine, G. A. Org. Prep. Proc. Int.
1995, 27, 469.