| Budget Amount *help |
¥3,700,000 (Direct Cost: ¥3,700,000)
Fiscal Year 2004: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 2003: ¥2,300,000 (Direct Cost: ¥2,300,000)
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| Research Abstract |
The carboxyl group in α-amino acids plays an important role as a proton donor and a peptide-bond-forming functional group. α-Amino acid analogs in which the carboxylic acid moiety is replaced with other acidic groups, e.g., phosphonic acid, sulfonic acid, boronic acid, tetrazole are known to be important surrogates of α-amino acid. Squaric acid is an oxocarbon and exhibits several unique physicochemical and chemical properties characterized by strong acidity, aromatic conjugate system, ring strain, electron deficiency, and metal chelating ability. Therefore, 4-hydroxy-2,3-dioxocyclobut-1-enyl (Sq) group has attracted much attention as an isostere of carboxylic acid in medicinal chemistry. In this project, the synthesis of a novel amino acid isostere bearing Sq group as a carboxylate equivalent in α-amino acid (α-Amino Squaric Acid (α-ASqA)) and its incorporation into peptide was implicated. We initially investigated facile and practical carbon-carbon bond-forming reaction to 1'-amino-1-squarylacetate followed by conversion of the resulting alkylated adducts into α-ASqA. Two novel methods involving the use of sq-group incorporating amino malonate equivalent (method A) and addition reaction of dianion enolate (method B) to access α-ASqA were developed. Addition reaction of dianion enolate generated from N-Boc-amino acid ester to squaric acid diisopropyl ester was the key to these methods. Generation efficiency of enolate from N-Boc-Phe-Ot-Bu ester was assessed by deuterium incorporation experiments using various bases. As a result, the use of 2 equiv of sec-BuLi was found to be the most efficient base. This result prompted two new methods A and B to access various α-ASqA possessing natural and unnatural types of α-amino acid side chain. α-ASqA was incorporated into Leu-enkephalin to give three different type of α-ASqA-containing Leu-enkephalin. These biological activities were characterized by receptor binding assay of opioid receptors.
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