Crystal Structure of Hybrid Dipeptide, Cytosinyl-L-Tyrosine
Mitsunobu DOI, Hajime MIYAKO, Akiko ASANO and Toshimasa ISHIDA
Analytical Sci., (1999) 15, 109-110.

This study was supported by the Grant-in-Aid for Scientific Research 07672427 from the Ministry of Education, Science, Sports and Culture.

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ORTEP-III (Burnett, 1996) drawing
Hybrid dipeptide was designed to investigate the cooperative interactions between the nucleic acid and polypeptide,1 and the structure property is similar to that of peptide nucleic acid (PNA). In this paper, we report the interaction between tyrosine and cytosine. The title compound (C-Tyr) was synthesized by the coupling 1-ethylcarboxy-cytosine and tyrosine methyl ester, and crystals were obtained from an aqueous methanol solution. There are two crystallographically independent molecules (Molecules 1 and 2) in the asymmetric unit and are discriminated by the differences in the torsion angles around C8-C9, N-CA and CB-CG which are related with the oriantations of aromatic rings. The molecules are folded with the similar mannerand, and the overall conformations are similar to each other. The turned conformation results the access between the cytosine base and the phenol ring, though no intramolecular interaction is observed. The C-terminal groups of tyrosine seem to be an unionized form (-COOH) in both molecules since the bond distances of C-O and C-OT are significantly differed. The cytosine bases interacte with these carboxyl groups: N41...O2, O2T...N31, N42...O1 and O2T...N31. In addition to these hydrogen bonds, the C-H...O hydrogen bonds are observed. In the C-Tyr crystal, the distances of H5...O9 and H6...O9 are below the sum of the van der Waals radii of hydrogen and oxygen (=2.7 A).

X-Ray Data Summary
formula2(C16 H18 N4 O5)
space groupP21
Cell Crystal
a (Ang) 9.5626(12) descriptionplate
b (Ang) 10.4539(12)colour colorless
c (Ang) 16.864(6) size (mm) 0.70x0.12x0.05
alpha (deg) 90.0 Dx (g/ml) 1.367
beta (deg) 93.218(17)F(000) 728
gamma (deg) 90.0 mu(CuKa) 0.870
V (Ang^3) 1683.1(6)
Z 2
Refinement Diffrn measurement
number_reflns2841 device typeRigaku AFC5R/RU-200
parameters 291 decay 3.0 %
restraints 0 index limit0-h-11,-12-k-0,-19-L-19
R_factor_all 0.0703theta (deg.) 2.62 - 64.87
R_factor_gt 0.0661total reflections2841
wR_factor_ref0.1890reflections(obs) 2721 .gt. 2sigma(I)
wR_factor_gt 0.1849Structure
shift/su_max lt.0.001solution SHELXS-97
shift/su_mean lt.0.001 refinement SHELXL-97

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Date: Jly.1998