&I ns.i I ( )r i--',hOO 1 2, India ' ( c'titrc' t o r Collular and Molecular Biology, R i y i i x i ' i l R i v . a r c ti Laboratory Campus, Hvdcrahad 5001 007, India Cyclolinopeptide A (CLPA), a cyclic nonapeptide, was isolated from linseed.") Its chemical structure is2
Prd -Pro2 -Phe3-Phe4 \ PU5 and i t has partial homology with the ionophore a n t a n ~a n i d e ~ in the sequence Pro-Pro-Phe-Phe. C I P A has been studied by theoretical and spectro-~c o p i c ~-~ methods to compare its three-dimensional structure and ionophoretic properties with those of antamanide. CLPA has been shown to inhibit the uptake of cholate into hepatocytes! A preliminary crystal structure of an orthorhombic form of CLPA monohydrate has recent1.y been reported?
In the present communication, we briefly report the structure of a triclinic form of CLPA dihydrate determined by x-ray diffraction. The natural peptide was crystallized from acetone-benzene mixtures. The determination of the lattice constants and intensity data collection were carried out on an Enraf Nonius CAD-4 diffractometer. Three standard reflections were measured at regular intervals in order to monitor crystal deterioration or misalignment. No variation in the intensities of these check reflections was observed during the entire period of data collection. A total of 5352 independent reflections were collected, 4665 of which were considered observed having Fobs > 3.00 (Fobs). Crystallographic details are reported in Table I.