Crystal structure of natural phaeosphaeride A

The asymmetric unit of the title compound, C15H23NO5, contains two independent molecules. Phaeosphaeride A contains two primary sections, an alkyl chain consisting of five C atoms and a cyclic system consisting of fused five- and six-membered rings with attached substituents. In the crystal, the molecules form layered structures. Nearly planar sheets, parallel to the (001) plane, form bilayers of two-dimensional hydrogen-bonded networks with the hydroxy groups located on the interior of the bilayer sheets. The network is constructed primarily of four O—H⋯O hydrogen bonds, which form a zigzag pattern in the (001) plane. The butyl chains interdigitate with the butyl chains on adjacent sheets. The crystal was twinned by a twofold rotation about the c axis, with refined major–minor occupancy fractions of 0.718 (6):0.282 (6).

The asymmetric unit of the title compound, C 15 H 23 NO 5 , contains two independent molecules. Phaeosphaeride A contains two primary sections, an alkyl chain consisting of five C atoms and a cyclic system consisting of fused five-and six-membered rings with attached substituents. In the crystal, the molecules form layered structures. Nearly planar sheets, parallel to the (001) plane, form bilayers of two-dimensional hydrogen-bonded networks with the hydroxy groups located on the interior of the bilayer sheets. The network is constructed primarily of four O-HÁ Á ÁO hydrogen bonds, which form a zigzag pattern in the (001) plane. The butyl chains interdigitate with the butyl chains on adjacent sheets. The crystal was twinned by a twofold rotation about the c axis, with refined major-minor occupancy fractions of 0.718 (6): 0.282 (6).
Keywords: crystal structure; natural phaeosphaeride A.
Phaeosphaeride A turned out to be an inhibitor of signal transduction and an activator of transcription 3 (STAT3)dependent signaling. It was reported to selectively inhibit STAT3/DNA binding with an IC 50 of 0.61 mM and to exhibit promising cell growth inhibition in STAT3-dependent U266 multiple myeloma cells with an IC 50 of 6.7 µM.
While the relative stereochemistry of phaeosphaeride A was deduced on the basis of NOE experiments, its absolute configuration remained undetermined (Maloney et al., 2006). Moreover, the attempts of total synthesis of phaeosphaeride A showed considerable differences in 1 H and 13 C NMR data between the synthetic and natural phaeosphaeride A (Kobayashi et al., 2011;Chatzimpaloglou et al., 2012Chatzimpaloglou et al., , 2014. In 2015, Kobayashi and colleagues established the relative and absolute configurations of natural phaeosphaeride A by completing the first total synthesis of ent-phaeosphaeride A (Kobayashi et al., 2015).
Our research group isolated phaeosphaeride A from a fungal strain belonging to the genus Phoma. Phaeosphaeride A was obtained as an optically active (-108.33 (c 0.06, CH 2 Cl 2 )) yellow glass. 1 H and 13 C NMR data as well as mass spectra of our phaeosphaeride A match with the data reported for Clardy's natural phaeosphaeride A (Maloney et al., 2006).
Optical rotation of Clardy's product (-93.6 (c 2.0, CH 2 Cl 2 )) and our phaeosphaeride A have the same sign. In this work we describe the crystal structure of natural phaeosphaeride A.

S2. Experimental
NMR spectra were recorded on a Bruker AVANCE III 400 MHz spectrometer in DMSO-d6. The same solvent was used as an internal standard. High-resolution mass spectra (HRMS) were recorded on a LTQ Orbitrap Velos spectrometer.
Optical rotations were determined on an Optical Activity AA-55 polarimeter using a 20 cm cell with a Na 589 nm filter.

S3. Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1.
H atoms bonded to C atoms were included in calculated positions and refined using a riding model, with U iso (H) set to 1.2U eq (C) and C-H = 0.97 Å for CH 2 groups, U iso (H) set to 1.5U eq (N) and C-H = 0.96 Å for CH 3 groups and U iso (H) set to 1.2U eq (N) and C-H = 0.93 Å for CH groups. All H atoms bonded to O atoms were located in a difference Fourier map and were refined with distance restraints and constrained displacement parameters OH 0.82 Å and U iso (H) set to 1.2U eq (O). The large thermal ellipsoid on C13 is characteristic for the distal end of long alkyl chains.
The structure of phaeosphaeride A ( Fig.1) was refined as rotational twin [by a two-fold rotation about (001)] with twin fractions of 0.718 (6) and 0.282 (6). The ′HKLF 5′ format file for the final refinement was generated by the TwinRotMat facility in Platon (Spek, 2009

S4. Geometry
The asymmetric unit contains two independent molecules of phaeosphaeride A (I and II) ( fig. 1). Each molecule of phaeosphaeride A (numbering of atoms of phaeosphaeride A is given according to Clardy (Maloney et al., 2006)) contains two primary sections; an alkyl chain consisting of C(13)-C(12)-C(11)-C(10)-C(9) atoms and a cyclic system consisting of five and six membered rings with adjacent atoms.

Figure 1
A view of molecules I (left) and II (right) of phaeosphaeride A. The atom numbering scheme is that of Maloney et al. (2006). Displacement ellipsoids are shown at the 50% probability level.

Figure 2
Projection of the layered crystal structure of phaeosphaeride A on the (100)

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq C1