SPOCC: A Resin for Solid-Phase Organic Chemistry and Enzymatic Reactions on Solid Phase ² Jo1 rg Rademann, Morten Grøtli, Morten Meldal,* and Klaus Bock Contribution from the Department of Chemistry, Carlsberg Laboratory, Gamle Carlsberg Vej 10, DK-2500 Valby, Denmark ReceiVed December 15, 1998 Abstract: SPOCC resin 1, a novel, highly permeable, polar support for chemical and enzymatic solid-phase methods, is presented. The synthesis of SPOCC resin is based on the cross-linking of long-chain poly(ethylene glycol) (PEG) terminally substituted with oxetane by cationic ring-opening polymerization, affording a polymer containing only primary ether and alcohol C-O bonds. The polymer was prepared using Et 2 O‚BF 3 as initiator either via bulk polymerization in solution or via suspension polymerization in silicon oil, the latter yielding a beaded resin. The polymerization reaction was investigated with respect to the effects of PEG chain length, the fraction of bisoxetanylated PEG, initiator amount, and temperature in order to vary the swelling, loading, and mechanical stability of the resin. Furthermore, the resin was derivatized with various functional groups and subsequently applied to peptide synthesis and organic reactions in both organic solvents and water. An N-terminal peptide aldehyde was generated on the solid phase and employed to synthesize peptide isosteres by nucleophilic addition of various ylides. Solid-phase glycosylation of peptides and enzymatic reactions were successfully performed with SPOCC resin. Enzymatic proteolytic cleavage of a resin-bound decapeptide on treatment with the 27 kDa protease subtilisin BNP′ demonstrated the accessibility of the interior of the SPOCC resin for enzymes. Introduction Solid-phase organic chemistry has evolved rapidly during the past few years mainly due to the enormous potential of peptide 1,2 and non-peptide libraries 3 in medicinal chemistry and chemical biology. The success of solid-phase organic chemistry depends crucially on the properties of the solid support. 4,5 Resins are preferred which are chemically inert to a broad range of reaction conditions, mechanically stable, and applicable in many solvents of different polarity. 5 In particular, resins swelling in water are attractive for use in enzymatic reactions and on-bead enzymatic assays. 6 The resins presently used for solid-phase organic chemistry are constructed predominantly from cross-linked polystyrene as polymer. 7 Although grafting of the polystyrene core with polar linear polymers such as poly(ethylene glycol) (PEG) may improve the swelling in polar solvents, 8-10 the PEG- grafted resins have shown limitations regarding their use in aqueous solvents and for enzymatic chemistry. 11 In contrast, a resin constructed with PEG as macromonomer can be fully compatible with water as first demonstrated by the synthesis of PEGA resin using radical polymerization of acrylamide- substituted PEG. 12,13 Characterized by high swelling volumes in both nonpolar solvents and water, PEGA has been success- fully applied in the synthesis of difficult peptide sequences 12 as well as solid-phase enzyme reactions. 14 The favorable swelling properties of PEGA and other resins constructed by the cross-linking of PEG chains can be attributed to the stretched helical superstructures adopted by PEG in aqueous solution. 15 However, many organic reactions are not compatible with PEGA resin because of its rich abundance of amide functionality. For example, solid-phase glycosylation was hampered by the presence of the amide groups in the solid support 16,17 which interacted with both the oxocarbenium ion intermediate from the carbohydrate donor and the Lewis acids employed for activation. Similarly, strong bases cannot be used with this type of resin because they may readily deprotonate the amide nitrogen. Consequently, a PEG resin was developed based on polyoxyethylene/polyoxypropylene copolymer (POEPOP), which contained only ether bonds, 18 and this has been successfully applied in the solid-phase organic synthesis of peptide iso- steres. 19 POEPOP could be prepared effectively by anionic * To whom correspondence should be addressed. ² SPOCC resin ) superpermeable organic combinatorial chemistry resin. (1) Lam, K. S.; Salmon, S. E.; Hersh, E. M.; Hruby, V. J.; Kazmierski, W. M.; Knapp, R. J. Nature 1991, 354, 82-84. (2) Houghten, R. A.; Pinilla, C.; Blondelle, S. E.; Appel, J. R.; Dooley, C. T.; Cuervo, J. H. Nature 1991, 354, 84-86. (3) Balkenhohl, F.; Bussche-Hu¨nnefeld, C. v. d.; Lansky, A.; Zechel, C. Angew. Chem., Int. Ed. Engl. 1996, 35, 2288-2337. (4) Hodge, P. C.; Sherrington, D. C. Polymer-supported reactions in organic chemistry; Wiley: Chichester, 1988. (5) Meldal, M. In Solid-Phase Peptide Synthesis; Fields, G., Ed.; Academic Press: New York, 1998; pp 83-104. (6) Meldal, M.; Svendsen, I.; Juliano, L.; Juliano, M. A.; Del Nery, E.; Scharfstein, J. J. Pept. Sci. 1998, 4, 83-91. (7) Merrifield, B. J. Am. Chem. Soc. 1963, 85, 2149-2153. (8) Becker, H.; Lucas, H.-W.; Maul, J.; Pillai, V. N. R.; Anzinger, H.; Mutter, M. Makromol. Chem., Rapid Commun. 1982, 3, 217-223. (9) Hellermann, H.; Lucas, H.-W.; Maul, J.; Pillai, V. N. R.; Mutter, M. Macromol. Chem. 1983, 184, 2603-2617. (10) Rapp, W.; Zhang, L.; Ha¨bish, R.; Bayer, E. In Peptides 1988, Proceedings of the European Peptide Symposium; Jung, G., Bayer, E., Eds.; Walter de Gruyter: Berlin, 1989; pp 199-201. (11) Burger, M. T.; Bartlett, P. A. J. Am. Chem. Soc. 1997, 119, 9, 12697-12698. (12) Meldal, M. Tetrahedron Lett. 1992, 33, 3077-3080. (13) Kempe, M.; Barany, G. J. Am. Chem. Soc. 1996, 118, 7083-7093. (14) Meldal, M.; Auzanneau, F.-I.; Hindsgaul, O.; Palcic, M. M. J. Chem. Soc., Chem. Commun. 1994, 1849-1850. (15) Tasaki, K. J. Am. Chem. Soc. 1996, 118, 8459-8469. (16) Rademann, J. Solid-phase syntheses with carbohydrates. Dissertation, University of Konstanz, Germany, 1997. (17) Schleyer, A.; Meldal, M.; Renil, M.; Paulsen, H.; Bock, K. Angew. Chem., Int. Ed. Engl. 1997, 109, 22064-2067. (18) Renil, M.; Meldal, M. Tetrahedron Lett. 1996, 37, 6185-6188. 5459 J. Am. Chem. Soc. 1999, 121, 5459-5466 10.1021/ja984355i CCC: $18.00 © 1999 American Chemical Society Published on Web 05/29/1999