LETTER
A Valuable Alternative to PyBOP for Solid Phase Peptide Synthesis
277
It is noteworthy to see that serine containing peptides can
be prepared without protection at the OH group (ES/MS
spectrum of 13: 677.6; C35H40N4O8S requires 676.26) and
that also proline can be easily coupled with high yields.
Comparing the results obtained using DMTMM with
those obtained using PyBOP, we are convinced that 2 is a
convenient and economical alternative to PyBOP12 (or to
other similar coupling agents) for batch manual solid
phase peptide synthesis on Wang resins following the
Fmoc protocol.
References and Notes
(1) Bodanszky, M.; Bodanszky, A. The Practice of Peptide
Synthesis, Springer-Verlag: Berlin, 1994; 75.
(2) Merrifield, B. In Peptides, Synthesis, Structures, and
Applications, B. Gutte Ed., Academic Press, San Diego: 1995;
94.
(3) a) Lee, H-W.; Kang, T.W.; Cha, K.H.; Kim, E-N.; Choi, N-H.;
Kim, J-W.; Hong, C.H. Synth. Commun. 1998, 28, 1339. b)
Hipskind, P. A.; Howbert, J.; Cho, S.; Cronin, J. S.; Fort, S. L.;
Ginah, F. O.; Hansen, G. J.; Huff, B. E.; Lobb, K. L.;
Martinelli, M. J.; Murray, A. R.; Nixon, J. A.; Staszak, M.;
Copp, J. D. J. Org. Chem. 1995, 60, 7033. c) Taylor, E. C.;
Dowling, J. E.; J. Org. Chem. 1997, 62, 1599. d) Nayyar, N.
K.; Hutchinson, D. R.; Martinelli, M. J. J. Org. Chem. 1997,
62, 982. e) Kaminski, Z. J. Synthesis 1987, 917. f) Kaminski,
Z. J. Tetrahedron Lett. 1985, 26, 2901.
Typical experimental procedure: DMT-Ala-Pro-Ile-Met-Leu-
Phe-Phe-Met-OH (17):
The synthesis was carried out in a manual 20 mL reactor equipped
with a sintered glass and using a nitrogen flow for agitation and fil-
tration. The 1% cross-linked polystyrene resin (Wang -type) pre-
loaded with Fmoc-Met (0.2 g of 0.52 mmol/g loaded beads, 0.1
mmol) was placed in the reactor and swollen for 2 hrs with N-meth-
ylpyrrolidinone (NMP) (5 mL). The Fmoc group was removed by
treatment with 25% piperidine in DMF (5 mL 1 x 6 min, 1 x 9 min)
(positive Kaiser’s test)6 and the resin was rinsed with DMF (6 x 2
min, 5 ml). The resin was treated with NMP (5 mL) and Fmoc-phe-
nylalanine (0.16 g, 0.4 mmol) was added to the suspension followed
by DMTMM (0.08 g, 0.3 mmol) and DIPEA (75 mL, 0.6 mmol). Af-
ter 5 min (negative Kaiser’s test)6 the resin was rinsed with DMSO
(2 x 2 min, 5 ml) and NMP (2 x 2min, 5 ml). The cycle of Fmoc
deprotection and coupling was repeated adding to the growing pep-
tides the following amino acids: Fmoc-Phe-OH (0.16 g, 0.4 mmol),
Fmoc-Leu-OH (0.15 g, 0.4 mmol), Fmoc-Met-OH (0.16 g, 0.4
mmol), Fmoc-Ile-OH (0.15 g, 0.4 mmol), Fmoc-Pro-OH (0.14 g,
0.4 mmol) (chloranil test),13 Fmoc-Ala-OH (0.13 g, 0.4 mmol). Af-
ter removal of the terminal Fmoc group and rinsing of the resin with
DMF, CDMT (0.07 g, 0.4 mmol) was added to the suspension of the
resin in NMP (5 mL), followed by the NMM (70 mL, 6 equiv). After
30 min (negative Kaiser’s test)6 the resin was rinsed with DMSO
(2 x 2 min, 5 mL), NMP (2 x 2min, 5 mL), CH2Cl2 (2 x 2min, 5
mL), and Et2O (2 x 2min, 5 mL), and dried under a nitrogen stream.
The resin was then suspended in a 20% solution of TFA in CH2Cl2
(10 mL) for 2 h. The resin was filtered off and the filtrate was evap-
orated under vacuum to give the DMT-protected octamer 17 (78
mg, 70%). ES/MS m/z: Found 1108.7 (C53H76N11O11S requires
1107.38).
(4) Falorni, M.; Porcheddu, A.; Taddei, M. Tetrahedron Lett.
1999, 40, 4395. Masala, S.; Taddei, M. Org. Lett. 1999,
1,1355. Falorni, M.; Giacomelli, G.; Porcheddu, A.; Taddei,
M. J. Org. Chem. 1999, 64, 8962.
(5) Kaminski, Z.J.; Paneth, P.; Rudzinski, J. J. Org. Chem. 1998,
63, 4248.
(6) Kaiser, E.; Colescott, R.L.; Bosinger, C.D.; Cook, P.I. Anal.
Biochem. 1970, 34, 595.
(7) The activation time preceding the coupling process has been
related to partial racemisation also in the case of phosphonium
salts, see: Albericio, F.; Cases, M.; Alsina, J.; Triolo, S.A.;
Carpino, L.A.; Kates, S.A. Tetrahedron Lett. 1997, 38, 4853
and references therein.
(8) Kunishima, M.; Kawachi, C.; Iwasaki, F.; Terao, K.; Tani, S.
Tetrahedron Lett. 1999, 40, 5327. Kunishima, M.; Morita, J.;
Kawachi, C.; Iwasaki, F.; Terao, K.; Tani, S. Synlett 1999,
1255. Kunishima, M.; Kawachi, C.; Morita, J.; Terao, K.;
Iwasaki, F.; Tani, S. Tetrahedron 1999, 55, 13159. Compound
2: mp 118-120 °C (lit 116-118 °C). Anal calcd for
C10H17ClN4O3: C 43.40, H 6.19, N 20.25. Found C 43.48; H
6.20, N 20.30.:
(9) For an analogous behaviour with isobutyl chloroformate see:
Shieh, W-C.; Carlson, J.A.; Shore, M.E. Tetrahedron Lett.
1999, 40, 7167.
(10) HPLC conditions: Column C-18-Lichrospher 100, 5mm,
250 x 4 mm, eluent MeCN/H20 (0.1% TFA) fron 80/20 to 20/
80 in 20 min. Detector UV lamp, l 254 nm, flow 1 mL / min.
(11) We followed the protocol described on the Novabiochem
Catalogue & Peptide Synthesis Handbook, 1999, Synthesis
Notes, S69.
Acknowledgement
(12) The price of PyBOP is 11.9 Euro per mmol, whereas the cost
of 2 (purchasing CDMT and NMM and considering a yield of
90%) is 1.5 Euro per mmol. Prices from Aldrich Catalogue
1999-2000, Italian Lira. Preparing CDMT from
trichlorotriazine and MeOH the cost is even lower.
(13) Vojkovsky, T. Pept. Res. 1995, 8, 236.
This work was financially supported by C.N.R. (Rome) within the
project N. 115.17963-1988
Article Identifier:
1437-2096,E;2000,0,02,0275,0277,ftx,en;G28299ST.pdf
Synlett 2000, No. 2, 275–277 ISSN 0936-5214 © Thieme Stuttgart · New York