[(3aS,5aR,8aR,8bS)-2,2,7,7-Tetramethyltetrahydro-3aH-bis[1,3]dioxolo[4,5-b:4′,5′-d]pyran-3a-yl]methyl (R)-N-(1-phenylethyl)sulfamate

In the title compound, C20H29NO8S, the two five-membered rings adopt envelope conformations (with an O atom at the flap in each case), while the six-membered pyran ring displays a twist-boat conformation. In the crystal, molecules are linked by N—H⋯O hydrogen bonds into a supramolecular chain running along the a axis.

In the title compound, C 20 H 29 NO 8 S, the two five-membered rings adopt envelope conformations (with an O atom at the flap in each case), while the six-membered pyran ring displays a twist-boat conformation. In the crystal, molecules are linked by N-HÁ Á ÁO hydrogen bonds into a supramolecular chain running along the a axis.
Data collection: SMART (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL. This work was supported by the program of the Education Department of Liaoning Province (No. L2010533), and the program of the Science and Technology Department of Liaoning Province, China (No. 2009226015-5 The marketed drug Topiramate is a moderate inhibitor of carbonic anhydrase-II(CA-II), which is marketed worldwide for the treatmen of epilepsy and the prophylaxis of migraine headache (Maryanoff et al., 2008). Topiramate easily qualifies as a "billion-dollar molecule". Given the disabling effects of epileptic seizures and the misery associated with recurrent migraine attacks, this drug has helped millions of patients in need across the globe (Maryanoff, 2009).
Topiramate is a sulfa-derivative monosaccharide, it contains a sulfamide group, but a sulfamate group is much more effective than the sulfamide group for inhibiting human CA-II (Maryanoff et al., 1998;Winum et al., 2006).
The O5 atom is located above the plane [deviations from the C10/N2/C13/C12 mean plane = 0.473 Å], while the O7 atom is located above the plane [deviations from the C12/ C13/ O8/C18 mean plane = 0.363 Å], Atom C7 of the title molecule is chiral: R configuration was assigned to this atom based on the known chirality of the equivalent atom in the starting material, otherwise, the C10, C11, C12, C13 of the title molecule is chiral: S, S, R, R, respectively. The suIfonyl O atom is engaged in H-bonding with the N-H of the adjacent molecular.

Refinement
The H atom of the NH group was located in a difference map, other H atoms were positioned with idealized geometry using a riding model with C-H = 0.93-0.98 Å. H atoms were refined in riding mode with U iso (H) = 1.2U eq (parent atom).

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.