1. Photochemical Preparation of (Glyco)Peptide- α -Thioesters Tyrone Hogenauer , Dr. Zefeng Cai, Yoon Ju Kim and Dr. Katja Michael The University of Texas at El Paso, Department of Chemistry INTRODUCTION SYN. OF PHOTOREACTIVE GLYCOPEPTIDES A novel technique called native chemical ligation (NCL) has emerged that allows for the total chemical synthesis of moderately sized proteins. A peptide with a C-terminal thioester is condensed with a second peptide that has an N-terminal cysteine. The two building blocks undergo trans -thioesterification in an aqueous buffer, under denaturing conditions, and the resulting thioester rapidly rearranges to produce a native peptide bond. Peptide- α -thioesters can be easily prepared by SPPS using the Boc protecting group strategy. However, the repeated use of strong acid during N-terminal deprotection steps would destroy carbohydrate residue linkages during the construction of glycopeptides/proteins. Methods for thioesterification that are compatible with the Fmoc protecting group strategy have been developed. However, their use is often limited due to a) the occurrence of unacceptable levels of C-terminal epimerization; b) hydrolysis of the activated carboxylic acid or thioester under basic conditions; or c) by the necessity of post chain assembly manipulations prior to thioesterification. Recently, this lab has offered a solution to these problems by developing a method for the photochemical acylation of thiols using N-aclynitroindolines under neutral conditions which results in peptide- α -thioesters with no epimerization. However, initial results produced peptide thioesters only in moderate yields due to two competing photolysis pathways. Contact information: inmybubble@hotmail.com; kmichael@utep.edu OBJECTIVE Mechanism of photolysis: Glycopeptide partial sequence Gly 411 - Pro 419 of gp120: 1. G. Papageorgiou and J. E. T. Corrie, Tetrahedron , 2000 , 56 , 8197. (b) J. Morrison, P. Wan, J. E. T. Corrie and G. Papageorgiou, Photochem. Photobiol. Sci ., 2002 , 1 , 960; (c) G. Papageorgiou, D. Ogden, G. Kelly and J. E. T. Corrie, Photochem. Photobiol. Sci ., 2005 , 4 , 887. 2. S. Pass, B. Amit and A. Patchornik, J. Am. Chem. Soc., 1981 , 103 , 7674. 3. K. C. Nicolaou, B. S. Safina and N. Winssinger, Synlett , 2001 , SI, 900. 4. T. J. Hogenauer, K. Michael, Org. Biomol. Chem ., 2007 , 5 , 759–762. Synthesis of Nitroindoline Linker for SPPS: OLD METHOD: ONE POT- “ONE STEP” RXN NEW METHOD: ONE POT- “TWO STEP” RXN Model reactions with photoreactive amino acids: Fmoc-AA-SPh : YIELD Fmoc-Gly-SPh 93% Fmoc-Ala-SPh 90% Fmoc-Pro-SPh 91% Fmoc-Ile-SPh 89% Fmoc-Phe-SPh 92% Fmoc-Glu(OBn)-SPh 90% Fmoc-Lys(Tfa)-SPh 84% Fmoc-Thr(OBn)-SPh 89% Fmoc-Tripeptide-Ind-SPh YIELD Fmoc-Ala-Ala-Pro-SPh 88% Fmoc-Leu-Gly-Ile-SPh 82% Fmoc-Lys(tfa)-Leu-Phe-SPh 89% Fmoc-Glu(OBn)-Ala-Lys(tfa)-SPh 82% Fmoc-Thr(OBn)-Ile-Thr(OBn)-SPh 89% Thioesterifications of photoreactive tripeptides: -Expand the developed methodology to short sequence glycopeptides from human erythropoeitin and the gp120 HIV envelope protein. -Use the developed methodologies for the total synthesis of a large glycopeptide using repetitive native chemical ligation (NCL) Glycopeptide partial sequence Asn 24 - Gly 28 of h-Epo: FUTURE WORK EXPERIMENTAL REFERENCES ACKNOWLEDGMENTS NSF grant CHE-0719538 (KM) Development of a highly efficient, photochemical, Fmoc-compatible solid phase synthesis of (glyco)peptide- α - thioesters.