Cyclo(-Cha-Oxz-D-Val-Thz-Ile-Oxz-D-Val-Thz-) N,N-dimethylacetamide dihydrate: a square form of cyclohexylalanine-incorporated ascidiacyclamide having the strongest cytotoxicity.

The title compound, 1-cyclohexylmethyl-1-de(1-methylpropyl)ascidiacyclamide N,N-dimethylacetamide dihydrate, C(39)H(56)N(8)O(6)S(2) x C(4)H(9)NO x 2H(2)O, a cyclohexylalanine-incorporated ascidiacyclamide analogue ([Cha]ASC), shows a square form similar to natural ASC. On the other hand, CD (circular dichroism) spectra showed [Cha]ASC to have a folded structure in solution, making it the second known analogue to show a discrepancy between its crystal and solution structures. Moreover, the cytotoxicity of [Cha]ASC (ED(50) = 5.6 micro g ml(-1)) was approximately two times stronger than that of natural ASC or a related phenylalanine-incorporated analogue, viz. cyclo(-Phe-Oxz-D-Val-Thz-Ile-Oxz-D-Val-Thz-) ([Phe]ASC), and was confirmed to be associated with the square form. However, [Phe]ASC was previously shown to be folded in the crystal structure, which suggests that the difference between the aromatic and aliphatic rings affects the molecular folding of the ASC molecule.