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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 35, Number 8
BKCSDE 35(8)
August 20, 2014 

Crystal Structure and Spectroscopic Properties of Cyclic Dipeptide: A Racemic Mixture of cyclo(D-Prolyl-L-Tyrosyl) and cyclo(L-Prolyl-D-Tyrosyl)
Yong Pyo Hong, Sung-Hong Lee, Jong-Ha Choi*, Ayana Kashima, Go Nakamura, Takayoshi Suzuki
Crystal structure, Conformation, rac-cyclo(D-Pro-L-Tyr/L-Pro-D-Tyr), Cyclic dipeptide, Spectral data
Two diastereoisomers of cyclo(Pro-Tyr) have been synthesized simultaneously. The crystal structures and conformations of both cyclo(L-Pro-L-Tyr) and a racemic mixture of cyclo(D-Pro-L-Tyr) and cyclo(L-Pro-DTyr), abbreviated as rac-cyclo(D-Pro-L-Tyr/L-Pro-D-Tyr), have been determined by a single-crystal X-ray diffraction study at low temperature. The crystals of rac-cyclo(D-Pro-L-Tyr/L-Pro-D-Tyr) belong to orthorhombic space group Pna21 with a = 10.755 (1), b = 12.699 (1), c = 9.600 (1) Å and Z = 4. The tyrosine side chain is folded towards the diketopiperazine (DKP) ring. The DKP ring adopts a twist boat conformation with pseudo symmetry C2v. The pyrrolidine ring has an envelope conformation with the N5, C4, C7 and C8 atoms in a plane. The crystal of rac-cyclo(D-Pro-L-Tyr/L-Pro-D-Tyr) is stabilized by hydrogen bonds between amide N2-H2 and carbonyl oxygen O2 in the neighbor. The hydroxyl group of tyrosine residue is also hydrogen bonded to the oxygen of the carbonyl group of the DKP ring in the next molecule. The spectroscopic properties of both isomers are also described.
2299 - 2303
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