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Paul W. R. Harris et al. / Tetrahedron Letters 52 (2011) 6024–6026
Table 2
Preparation of ACP (65–74) or oxytocin using amino methyl resins 3, 4, or 5
Resin
Scale (mmol)
Peptide
Calculated weight of
peptide resin (mg)
Weight of peptide
resin (mg)
Calculated weight
of crude product (mg)
Weight of crude
product (mg)
Purity (%)
3a
4b
5c
3a
4b
5c
0.086
0.075
0.087
0.086
0.075
0.087
ACP (65–74)
ACP (65–74)
ACP (65–74)
Oxytocin
Oxytocin
Oxytocin
256
236
258
299
274
301
248
225
252
276
263
288
91.4
79.9
92.5
86.7
75.6
87.8
74.5
66.1
82.5
75.3
65.3
82.2
86
89
86
79
75
86
a
b
c
Loading 0.86 mmol/g.
Loading 0.75 mmol/g.
Loading 0.87 mmol/g.
and oxytocin afforded crude products in excellent purity and good
recovery which compared well to resin 3 obtained from the hydra-
zine protocol. We have used resin 5 exclusively for the preparation
of many (>50) polypeptides by Fmoc- or Boc-SPPS, the results of
which will be communicated in the subsequent publications.
Acknowledgment
The authors wish to thank The Maurice Wilkins Centre for
Molecular Biodiscovery for the financial support (P.W.R.H.).
References and notes
Figure 2. RP-HPLC of crude ACP (65–74) synthesized on aminomethyl resins 3, 4, or
5. Column C18 Gemini 2.0 Â 50, gradient 5–30% B (1% B/min), A = 0.1% TFA–H2O,
B = 0.1% TFA–MeCN.
1. Merrifield, R. B. J. Am. Chem. Soc. 1963, 85, 2149–2154.
2. Pugh, K. C.; York, E. J.; Stewart, J. M. Int. J. Pept. Prot. Res. 1992, 40, 208–213.
3. MacDonald, A. A.; Dewitt, S. H.; Ghosh, S.; Hogan, E. M.; Kieras, L.; Czarnik, A.
W.; Ramage, R. Mol. Diversity 1996, 1, 183–186.
4. Meldal, M. In Solid Phase Peptide Synthesis; Fields, C. G., Ed.; Academic Press:
New York, 1988; pp 83–104.
5. Yan, B. Comb. Chem. High Throughput Screening 1988, 215–229.
6. Harris, P. W. R.; Brimble, M. A. Synthesis 2009, 3460–3466.
7. Bouillon, I.; Soural, M.; Miller, M. J.; Krchnak, V. J. Comb. Chem. 2009, 11, 213–
215.
8. Deng, F. K.; Mandal, K.; Luisier, S.; Kent, S. B. H. J. Pept. Sci. 2010, 16, 545–550.
9. Alewood, D.; Hopping, G.; Brust, A.; Reid, R. C.; Alewood, P. F. J. Pept. Sci. 2010,
16, 551–557.
10. Mitchell, A. R.; Kent, S. B. H.; Engelhard, M.; Merrifield, R. B. J. Org. Chem. 1978,
43, 2845–2852.
11. Meisenbach, M.; Allmendinger, T.; Mak, C. P. Org. Process Res. Dev. 2003, 7, 553–
558.
12. Adams, J. H.; Cook, R. M.; Hudson, D.; Jammalamadaka, V.; Lyttle, M. H.;
Songster, M. F. J. Org. Chem. 1998, 63, 3706–3716.
Figure 3. RP-HPLC of crude oxytocin synthesized on aminomethyl resins 3, 4, or 5.
Column C18 Gemini 2.0 Â 50, gradient 5–30% B (1% B/min), A = 0.1% TFA–H2O,
B = 0.1% TFA–MeCN.
13. Ljungdahl, N.; Martikainen, L.; Kann, N. Tetrahedron Lett. 2008, 49, 6108–6110.
14. Zikos, C. C.; Ferderigos, N. G. Tetrahedron Lett. 1995, 36, 3741–3744.
15. Zikos, C.; Alexiou, G.; Ferderigos, N. Tetrahedron Lett. 2006, 47, 8711–8715.
16. Mitchell, A. R.; Kent, S. B. H.; Erickson, B. W.; Merrifield, R. B. Tetrahedron Lett.
1976, 3795–3798.
acetonitrile, and lyophilized. The results are given in Table 2 and
Figures 2 and 3.
17. Lee, T. K.; Ryoo, S. J.; Byun, J. W.; Lee, S. M.; Lee, Y. S. J. Comb. Chem. 2005, 7,
170–173.
18. Garibay, P.; Toy, P. H.; Hoeg-Jensen, T.; Janda, K. D. Synlett 1999, 1438–1440.
19. Ref. 9 used MeNH2 for de-phthalimidomethylation resulting in a soluble by-
product but requiring 16 h to complete.
20. Swelling (in CH2Cl2) of 1% DVB–PS is 8 mL/g, swelling of 2 was 8.1 mL/g.
21. N-Phthalimidomethyl resin 2 was prepared as outlined in Ref. 5 A 250 mL
round-bottomed flask was charged with N-phthalimidomethyl resin 2 (6.02 g),
20% (v/v) ethanolamine in absolute EtOH (AR, 100 mL) and the mixture is
refluxed by stirring for 7 h. The resulting mixture was cooled to room
temperature and washed successively with EtOH (100 mL), DMF (100 mL),
and CH2Cl2 (100 mL) and dried in vacuo to afford resin 5 (5.01 g, 94%) as a
white solid. IR analysis showed an absence of carbonyl absorptions. Elemental
analysis gave 1.22% N corresponding to a loading of 0.87 mmol/g.
22. Rink, H. Tetrahedron Lett. 1987, 28, 3787–3790.
For aminomethyl resins 3, 4, and 5 the weight of the peptide re-
sin following assembly by SPPS was comparable to that antici-
pated. The quantities recovered and the purities of the crude
products, obtained after cleavage from the resin, as estimated by
analytical HPLC (Figs. 2 and 3), were also similar although the high-
est recoveries were found for aminomethyl resin 5. Therefore,
based on the data presented in Table 1, it is evident that either
of the dephthalimidomethylation methods using benzylamine or
2-aminoethanol can be used confidently for the preparation of
AM-PS resin.
In conclusion, we have demonstrated that for the preparation of
AM-PS resin by phthalimidomethylation–dephthalimidomethyla-
tion on polystyrene resin, the common dephthalimidomethylation
reagent hydrazine can be replaced effectively by 2-aminoethanol
or benzylamine. Significantly, the use of 2-aminoethanol or benzyl-
amine enabled the resultant aminomethyl-functionalized polysty-
rene resin to be easily separated from highly soluble by-products
by filtration using minimal solvent washing. Fmoc-SPPS of amino-
methyl resins 4 or 5 for the synthesis of the peptides ACP (65–74)
23. Albericio, F.; Barany, G. Int. J. Pept. Prot. Res. 1985, 26, 92–97.
24. General procedure for peptide synthesis with aminomethyl resins: For ACP (65–
74); resin
5 (0.1 g) was swelled in CH2Cl2 and reacted with FmocGly-
OCH2PhOCH2CH2CO2H (2 equiv) and diisopropylcarbodiimide (DIC) (2 equiv)
in CH2Cl2 for 1 h. The Kaiser test was negative. For oxytocin; resin 5 (0.1 g) was
swelled in DMF and reacted with Rink linker (3 equiv), HOBt (3 equiv), and
diisopropylcarbodiimide (DIC) (3 equiv) in DMF for 1 h. The Kaiser test was
negative. All Fmoc-SPPS was performed using a Tribute 2 channel peptide
synthesizer (Protein Technologies, Tucson, Az) using a 2 Â 5 min deprotection
with 20% (v/v) piperidine/DMF, followed by 5 Â 30 s DMF washes. Coupling
was performed for 30 min with Fmoc-Aa (5 equiv), HBTU (4.6 equiv) and DIPEA
(10 equiv) followed by a 5 Â 30 s DMF wash.