Cyclolinopeptide K butanol disolvate monohydrate

The title compound, C56H83N9O11S·2C4H10O·H2O, is a butanol–water solvate of the cyclolinopeptide cyclo(Metsulfone1-Leu2–Ile3–Pro4–Pro5–Phe6–Phe7–Val8–Ile9) (henceforth referred to as CLP-K) which was isolated from flax oil. All the amino acid residues are in an l configuration based on the CORN rule. The cyclic nonapeptide exhibits eight trans peptide bonds and one cis peptide bond observed between the two proline residues. The conformation is stabilized by an α- and a β-turn, each containing an N—H⋯O hydrogen bond between the carbonyl group O atom of the first residue and the amide group H atom of the fourth (α-turn) and the third residue (β-turn), repectively. In the crystal, the components of the structure are linked by intermolecular N—H⋯O and O—H⋯O hydrogen bonds into a two-dimensional network parallel to (001). The –C(H2)OH group of one of the butanol solvent molecules is disordered over two sets of sites with refined occupancies of 0.863 (4) and 0.137 (4).

All the amino acid residues in CLP-K are in the L configuration based on the CORN rule. This is also supported by the L configuration of the amino acid residues in the corresponding cyclolinopeptide C, cyclo(Metsulfoxide 1 -Leu 2 -Ile 3 -Pro 4 -Pro 5 -Phe 6 -Phe 7 -Val 8 -Ile 9 ), determined using derivative chemistry (Morita et al., 1999). Applying the Cahn-Ingold-Prelog priority rules (Cahn et al., 1966), the configuration at the chiral α-C atom of each amino acid residue is S. The standard uncertainty u = 0.05 at Flack parameter x = 0.13 implies an enantiopure-sufficient inversion-distinguishing power and together with 2u < x < 3u one cannot say that the crystal is truly enantiopure (Flack & Bernardinelli, 2000). However, the results of the absolute structure determination based on Bayesian statistics on Bijvoet differences (Hooft et al., 2008) using PLATON (Spek, 2009) indicate that it is very probable that the absolute configuration has been correctly assigned. The obtained value for the absolute structure parameter y was 0.082 (9).
The cyclolinopeptide exhibits eight trans peptide bonds with values for ω ranging from 166.49 (14) to 179.30 (14)° (see Table 2) and one cis peptide bond observed between the two proline residues (ω = 1.5 (2)°) (see Table 2). The conformation of the cylic peptide is stabilized by an α-and β-turn each containing a hydrogen bond between the carbonyl oxygen of the first residue and the amide hydrogen of the fourth (α-turn) and the third residue (β-turn), repectively. The 5→1 NH···O=C contact bond (α-turn) involves the amide group of Phe 7 and carbonyl group of Ile 3 with the two cis bonded proline residues Pro 4 and Pro 5 being part of this α-turn. The β-turn, a 4→1 NH···O=C contact bond, is formed between the amide group of Ile 3 and carbonyl group of Ile 9 . The presence of these turns leads to a twisted conformation of CLP-K with an almost V-shaped part at Pro 5 as depicted in Fig. 2. The side chains of Metsulfone 1 , Leu 2 , Ile 3 , Phe 6 , Phe 7 , Val 8 , Ile 9 all adopt the gauche(+) conformation based on their χ 1 torsion angles (see Table 2).
supplementary materials sup-2 One of the oxygen atoms (labelled as O (1)) of the CLP-K methylsufonyl group is linked to a symmetry-related CLP-K unit via a S=O···(H)N contact bond (see Table 1). In addition, the CLP-K units are connected via the water molecule through hydrogen bonds involving one carbonyl group of each peptide and the hydrogen atoms of the water molecule (see Table 1).
These hydrogen bonds together with the S=O···(H)N interconnections are responsible for the formation of a two-dimensional network parallel to (001). The two butanol solvent molecules also form hydrogen bonds with CLP-K (see Table 1). The -C(H 2 )-OH group of one of the butanol solvent molecules is disordered over two sites with refined occupancies of 0.863 (4) and 0.137 (4). The anisotropic displacement parameters of the atoms O71A and O71B, C70A and C70B were constraint to be identical.

Experimental
Crystals of CLP-K were obtained via vapor diffusion, also known as isothermal distillation, at ambient temperature. CLP-K (10 mg) was dissolved in butanol (50 µL) and multiple snowflake-like crystals of CLP-K started to form after fifteen days upon diffusion of n-hexane into the sample solution at ambient temperature. The crystalline material was redissolved by adding n-butanol (100 uL) and single rod-like crystals of CLP-K, suitable for crystallographic studies, were obtained after eight days.

Refinement
A suitable single-crystal was removed from the solution, quickly coated with oil (Paratone 8277, Exxon), collected inside a mounted CryoLoop TM (diameter of the nylon fiber: 10 microns; loop diameter 0.1-0.2 mm) and then quickly transferred to the cold stream of the Oxford cryo-jet. The mounted CryoLoop TM had been attached prior to a copper wire (thickness, 0.6 mm; length: 18 mm) attached to a magnetic base using epoxy. Intensity data were collected at 100 K using the beamline 08B1-1 (CMCF-BM; Canadian Light Source, CLS) equipped with a ACCEL MD2 microdiffractometer and a 300 mm 16 K Rayonix MX300 HE CCD detector. The wavelength was set to 0.68878 Å and the distance between the detector and the crystal to 150 mm. The initial screening and data collection was performed with the Macromolecular Crystallography Data Collector (MXDC) graphical user interface. A series of data frames at 1° increments of ω were collected. The integrated intensity data were merged and corrected for absorption using SADABS (6, 1 harmonics). The final unit-cell parameters are based upon the refinement of the XYZ weighted centroids of 9248 reflections above 20 σ(I) with 4.67° < 2θ < 54.71°.