Dual activation of the glucagon-like peptide 1 (GLP-1) and glucagon receptor has the potential to lead to a novel therapy principle for the treatment of diabesity. Here, we report a series of novel peptides with dual activity on these receptors that were discovered by rational design. On the basis of sequence analysis and structure-based design, structural elements of glucagon were engineered into the selective GLP-1 receptor agonist exendin-4, resulting in hybrid peptides with potent dual GLP-1/glucagon receptor activity. Detailed structure-activity relationship data are shown. Further modifications with unnatural and modified amino acids resulted in novel metabolically stable peptides that demonstrated a significant dose-dependent decrease in blood glucose in chronic studies in diabetic db/db mice and reduced body weight in diet-induced obese (DIO) mice. Structural analysis by NMR spectroscopy confirmed that the peptides maintain an exendin-4-like structure with its characteristic tryptophan-cage fold motif that is responsible for favorable chemical and physical stability.

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High-resolution crystal structures of Staphylococcus aureus methionine aminopeptidase I in complex with various keto heterocycles and aminoketones were determined, and the intermolecular ligand interactions with the enzyme are reported. The compounds are effective inhibitors of the S. aureus enzyme because of the formation of an uncleavable tetrahedral intermediate upon binding. The electron densities unequivocally show the enzyme-catalyzed transition-state analogue mimicking that for amide bond hydrolysis of substrates.

The possibility of peptide assembly in the N-C direction by using HOBt salts of the amino acid 9-fluorenylmethyl esters has been investigated. The first amino acid derivative has to be coupled with the N-terminus to the polymer-bound trityl linker. Determination of the loading with the first amino acid derivative could be carried out according to the same method as for Fmoc-amino acids on the resin. Kinetic measurements were made of both the coupling of the amino acid derivatives during chain elongation, and the cleavage of the peptide from the resin. Several C-terminally modified peptides were synthesized with chain elongation being monitored by UV as it is standard practice in peptide synthesis in the usual direction. Particular attention was paid to racemization that may possibly occur.The method of synthesizing peptides on a solid phase in the C-to-N direction has become firmly established since its introduction in 1963 by Merrifield['l, but few attempts have been made to couple in the inverse d i r e~t i o n~~~~~~~~~~~~~~~~~~. The important advantage of an inverse synthesis is that it allows the direct synthesis of peptides with modifications at the C-terminus (amides, esters). C-terminally modified peptides are often found in nature and are potentially interesting for therapeutical use. Additionally, this methodology creates C-terminally protected peptide fragments that can be readily used for fragment condensation. Based on our method for the preparation of peptide amides via the HOBt ammonium saltsL81, we have investigated the possibility of peptide assembly in the N-C direction analogously, by using the HOBt salts of the amino acid 9-fluorenylmethyl est e r~ [~l [ '~l [~~] .These esters can be cleaved with 20% piperidine in DMF. The attachment of the amino acid derivatives to our new trityl linker [121[13] on the TentaGel resin is possible with all amino acids. Results and Discussion Preparation of the HOBt Salts of the Amino Acid Flnorenylmethyl EsterCommercially available Boc-amino acids were esterified by means of fluorenyl-methanol, DIC and DMAP. After cleavage of the Boc group with 1.2 N HCl in acetic acid to the resulting hydrochloride of the amino acid fluorenyl- Loading of the First Amino Acid Derivative onto the ResinThe linker p-(diphenylhydroxymethy1)benzoic acid was first coupled to amino-functionalized TentaGel[171 by means of HOBtIDIC and subsequently chlorinated at the trityl position with acetyl chlorideldichloromethane (1 :I). The trifluoroacetate of an amino acid fluorenylmethyl ester, obtained by treating Boc-amino acid fluorenylmethyl esters with 50% TFA in DCM, was added together with DIEA (Scheme 2). Reaction yields of 85-100% were obtained. Similar yields were obtained using the p-toluene sulfonates whereas hydrochlorides give only about 50% yield and HOBt salt about 10% under the same conditions. Amino acid fluorenylmethyl ester tosylates are generated by suspending the amino acid, p-toluenesulfonic acid and fluorenylmethanol in CHCI3. Refluxing this suspension with a Dean-Star...