2000;39:12450C12456. in values for these compounds. As shown in Physique 2, the characteristic peaks, assigned by 1H-NMR COSY experiments are HD (0.04 ppm difference for HD), HC (0.01 ppm difference for HC). All these protons showed more downfield shift for compound 9b. The most prominent downfield shift was observed for HD protons of isomer 9b in comparison to isomer 9a. HPLC analysis showed that isomer 9a has lower retention time compared to isomer 9b. The absolute configuration of the tetrahydrofuro[3,2-(nM)
1. Open VD3-D6 in a separate windows
3a10.92. Open in a separate windows
3b553.73. Open in a separate windows
3c110.54. Open in a separate windows
3d279.95. Open in a separate windows
3e28.16. Open in a separate windows
3f6307. Open in a separate windows
3g808.68. Open in a separate windows
3h41249. Open in a separate windows
3i41,12610. Open in a separate windows
3j28,758 Open in a separate window To gain molecular insight into the BACE1-inhibitor interactions, we decided the X-ray crystal structure of inhibitor 3a bound VD3-D6 to BACE1 at 2.85 ? resolution (Rfree = 21.9%, Rwork=17.2%).25 Methods for BACE1 co-crystallization with VD3-D6 3a and X-ray data collection are provided in Supplementary Data along with the final X-ray data collection and refinement statistics. A wall-eye stereoview of the active site of BACE1 with its interactions with inhibitor 3a is usually shown in Physique 3. The transition-state hydroxyl group at the Leu-Ala isostere forms two hydrogen bonds (2.4 ? and 2.8 ? bond distances) with active site aspartic acid residues Asp32 and Asp228 respectively.16 The P2-methylcysteine side chain appears to be involved in van der Waals interactions with Thr72, Gln73, Thr231 and Arg235 in the S2 subsite. The other inhibitor-BACE1 interactions due to P1, P1, and P2 ligands are very similar to Leu-Ala hydroxyethylene isostere-derived BACE1 inhibitors reported by us previously.17,26 Open in a separate window Determine 3 Stereoview (wall-eye) of the X-ray structure of inhibitor 3a VD3-D6 (green carbon chain) bound to BACE1 (grey carbon chain). Chain B in the asymmetric unit is shown. Potential hydrogen bonds between the inhibitor and BACE1 are shown as black dotted lines. The PDB code for this structure is usually 6DHC. The P3 bicyclic tetrahydrofuranyl isoxazoline occupies the S3 subsite and it is involved in a number of key van der Waals (VDW) interactions with BACE1 including the backbone carbonyl oxygens of Gly11 and Gly230; the alpha-carbon hydrogen of Gln12; and the side chains of Leu30, Ile110, Trp115 and Thr232 (Physique 3). The shape of the BACE1 pocket surrounding the bicyclic tetrahydrofuranyl isoxazoline is usually shown in Physique 4. The bicyclic group is usually partially solvent uncovered, and the surrounding pocket is usually electrostatically almost neutral. No hydrogen bonds are observed between BACE1 and the oxygens or nitrogen of the bicyclic tetrahydrofuranyl isoxazoline heterocycle. The ring junction stereochemistry (3aR, 6aS) of the bicyclic ligand allows for more optimal VDW interactions within the active site. In contrast, the corresponding (3aS, 6aR) stereochemistry in inhibitor 3b appears to disrupt these favorable VDW interactions and this may explain nearly 50-fold variations in BACE1 inhibitory activity for inhibitor 3a. Open up in another window Shape 4 Stereoview (wall-eye) of inhibitor 3a (green carbon string) destined to BACE1 (surface area representation). The solvent subjected surface area of BACE1 can be shown and it is coloured relating to Coulombic electrostatic potential (adverse = reddish colored, zero = white, positive = blue). Ideals are shaded from VD3-D6 ?20 to 20 in kcal/mol*e and so are shown in the colour key. The extreme reddish colored in the energetic site may be the consequence of the catalytic aspartates (Asp32 and Asp228). Potential hydrogen bonds between your inhibitor and BACE1 are demonstrated as yellowish lines. The carboxamide carbonyl group forms a hydrogen relationship using the Thr232 backbone NH. It really is Ecscr involved with a water-mediated hydrogen also.