Crystal structure of 2-[N-(t-butoxycarbonyl)amino]-4-(thymin-1-yl)-butyric acid methyl ester.

psuedopeptide backbone composed of N-(2-aminoethyl) glycine units, and nucleobases are attached by methylene carbonyl linkers (Fig. 1). Since the binding of PNA to DNA inhibits transcription, the potential of PNA has been focused to target an antisense drug.1 Moreover, PNA-peptides hybridization and improvements of the PNA backbone unit were developed to form DNA-DNA-PNA triplexes with nonspecific sequences.2,3 New PNA (α-PNA) has a backbone composed of L-homoserine and glycine, and the nucleobases are linked to the Cα atom through the ethylene group (Fig. 1). The most important property of α-PNA is a flexible linkage from the backbone to nucleobase in comparison with PNA. The title compound (Boc-hSeT-OMe) is one component of αPNA, and was synthesized from t-butoxycarbony-L-homoserine methyl ester (Boc-hSer-OMe) according to a previous report.3 Boc-hSer-OMe was bromininated by N-bromosuccinimide (NBS) under the existence of triphenylphosphine at room temperature, and alkylation of thymine was performed by heating a mixture of purified Boc-hSer(Br)-OMe and thymine with anhydrous potassium carbonate at 80 ̊C. Boc-hSeT-OMe was coupled with glycine methyl ester after saponification, giving Boc-hSeT-Gly-OMe (α-PNA (T) unit). Various conditions were attempted to crystallize both Boc-hSeT-OMe and Boc-hSeT-Gly-OMe, and thin-needle crystals of Boc-hSeTOMe (0.20 × 0.026 × 0.019 mm3) were finally grown from 361 ANALYTICAL SCIENCES FEBRUARY 2001, VOL. 17 2001 © The Japan Society for Analytical Chemistry