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Synlett 2003(14): 2216-2218  
DOI: 10.1055/s-2003-42054
LETTER
© Georg Thieme Verlag Stuttgart · New York

Rapid and Efficient Methodology to Perform Macrocyclization Reactions in Solid-Phase Peptide Chemistry

Paolo Grieco*, Pietro Campiglia, Isabel Gomez-Monterrey, Teresa Lama, Ettore Novellino
Dipartimento di Chimica Farmaceutica e Tossicologica, University of Naples ‘Federico II’, Via D. Montesano, 49, 80131, Naples, Italy
Fax: +39(081)678644; e-Mail: pagrieco@unina.it;
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Publikationsverlauf

Received 2 July 2003
Publikationsdatum:
07. Oktober 2003 (online)

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Abstract

Solid-phase peptide synthesis and microwave-assisted organic synthesis have been combined in order to speed up drug discovery process of macrocyclization products in high purity and good yield.

Key words

solid-phase peptide synthesis - macrocyclization - ­microwave synthesis

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General Procedure. All experiments were carried out in a Milestone CombiChem Microwave Synthesizer with vessels of 4 mL volume, using DMF as solvent. In all irradiation experiments, rotation of the rotor, irradiation time, temperature, and power were monitored with the ‘easyWAVE’ software package. Temperature was monitored with the aid of an optical fiber inserted into one of the reaction containers. Once 50 °C was reached the reaction mixture was held at this temperature for 10 min and then cooled rapidly to r.t. The reaction vessels were opened and the contents were poured into a separating funnel. The compounds were washed and subjected to the final cleavage from the resin. The crude product was precipitated by anhyd diethyl ether and recovered by filtration. All final products were purified by reverse-phase HPLC carried out on Vydac C-18 column with the following dimensions: 25 × 0.46 cm for analysis and 25 × 2.2 cm for preparative work. Flow rate applied were 1.0 mL/min (C18 column, linear gradient 10-90% MeCN/H2O in 40 min) and 5.0 mL/min for analytical and preparative HPLC, respectively. Analysis of purified products was performed by reverse-phase HPLC, 1H NMR and mass spectroscopy.

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Compound 1: C45H48N8O10S, M.W.: 892.98. MS (ESI, EI+): m/z = 892.7 (M+). HPLC: k’ = 5.85. 1H NMR (500 MHz, DMSO-d 6): δ = 10.48 (s, 1 H), 9.14 (s, 1 H), 8.97 (d, 1 H), 8.29 (d, 1 H), 8.22 (d, 1 H), 8.04 (d, 1 H), 7.86 (s, 1 H), 7.80 (d, 1 H), 7.68 (d, 1 H), 7.58 (m, 2 H), 7.33 (d, 1 H), 7.27-7.16 (m, 6 H), 7.07 (t, 1 H), 6.99 (t, 1 H), 6.88 (d, 2 H), 6.59 (d, 2 H), 4.52 (m, 1 H), 4.46 (m, 1 H), 4.43 (m, 1 H), 4.28 (m, 1 H), 3.83 (m, 1 H), 3.41 (m, 1 H), 3.30 (m, 2 H), 3.13 (dd, 1 H), 2.99 (q, 1 H), 2.92 (dd, 1 H), 2.79 (m, 1 H), 2.63 (m, 2 H), 1.56 (m, 2 H), 1.48 (m, 1 H), 1.34 (q, 1 H), 1.23 (m, 1 H), 1.06 (m, 1 H). Compound 2: C45H55N9O10, M.W.: 918.00. MS (ESI, EI+): m/z = 918.2 (M+). HPLC: k’ = 5.93. 1H NMR (500 MHz, DMSO-d 6): δ = 10.87 (s, 1 H), 9.35 (s, 1 H), 8.91 (d, 1 H) 8.38 (d, 1 H), 8.18 (d, 1 H), 8.01 (d, 1 H), 7.57 (m, 2 H), 7.47 (d, 1 H), 7.22-7.16 (m, 3 H), 7.15-7.04 (m, 5 H), 7.00 (m, 1 H), 6.98 (t, 1 H), 6.76 (d, 2 H), 6.65 (d, 2 H), 4.38 (m, 1 H), 4.31 (m, 1 H), 4.22-4.18 (m, 3 H), 3.23 (m, 2 H), 3.16 (m, 1 H), 3.10 (m, 1 H), 2.95 (m, 1 H), 2.84 (m, 1 H), 2.67 (m, 1 H), 2.62-2.59 (m, 3 H), 1.70 (m, 1 H), 1.56-1.53 (m, 2 H), 1.46-1.44 (m, 3 H), 1.37-1.36 (m, 4 H), 1.16-1.12 (m, 3 H), 1.06-1.03 (m, 1 H). Compound 3: C45H49N9O9S, M.W.: 891.99. MS (ESI, EI+): m/z = 891.3 (M+). HPLC: k’ = 5.78. Compound 4: C48H56N10O9, M.W.: 917.02. MS (ESI, EI+): m/z = 917.4 (M+). HPLC: k’ = 5.88.

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All reactions were performed on a scale of 100 mg of beads (0.7 mmol/g) allowing the isolation of at least 10 mg of crude product.