Synthesis of a muscarinic receptor antagonist via a diastereoselective Michael reaction, selective deoxyfluorination and aromatic metal-halogen exchange reaction.

An efficient synthesis of a structurally unique, novel M(3) antagonist 1 is described. Compound 1 is conveniently disconnected retrosynthetically at the amide bond to reveal the acid portion 2 and the amine fragment 3. The synthesis of key intermediate 2 is highlighted by a ZnCl(2)-MAEP complex 19 catalyzed diastereoselective Michael reaction of dioxolane 7 with 2-cyclopenten-1-one (5) to establish the contiguous quaternary-tertiary chiral centers and a subsequent geminal difluorination of ketone 17 using Deoxofluor in the presence of catalytic BF(3).OEt(2). The synthesis of the amine moiety 3 is highlighted by the discovery of a novel n-Bu(3)MgLi magnesium-halogen exchange reaction for selective functionalization of 2,6-dibromopyridine. This new and practical metalation protocol obviated cryogenic conditions and upon quenching with DMF gave 6-bromo-2-formylpyridine (26) in excellent yield. Further transformations afforded the amine fragment 3 via reductive amination with 35, Pd-catalyzed aromatic amination, and deprotection. Finally, the highly convergent synthesis of 1 was accomplished by coupling of the two fragments. This synthesis has been used to prepare multi-kilogram quantities of the bulk drug.

A comparison of structural relationships among alpha-crystallin, human Hsp27, gamma-crystallins and beta B2-crystallin.

The 3D structures of alpha-crystallin, a major eye lens protein, and related small heat shock proteins are unresolved. It has been assumed that alpha-crystallin is primarily a beta-sheet globular protein similar to alpha-crystallin (Siezen and Argos, Biochim. Biophys. Acta, 1983, 748, 56-67) containing sequence repeats in its two domains (Wistow, FEBS Lett. 1985, 181, 1-6). Positional flexibility of amino acid residues and far UV-circular dichroism spectroscopy were used to investigate structural relationships among these proteins. The utility of flexibility plots for predicting protein structure is demonstrated by the excellent correlation of these plots with the known 3D X-ray structures of beta/gamma-crystallins. Similar analyses of alpha-crystallin subunits, alpha A and alpha B, and human heat shock protein 27 show that the C-terminal domains and connecting segments of these proteins are very similar while the N-terminal domains have significant structural differences. Unlike beta/gamma-crystallins, both Hsp27 and alpha-crystallin subunits are asymmetrical with highly flexible C-terminal domains. Flexibility is considered essential for protein functional activity. Therefore, the C-terminal region may play an active role in alpha-crystallin and small heat shock protein function. Differences in flexibility profiles and estimated secondary structure distribution in alpha-crystallin by three recent/updated algorithms from far UV-CD spectra support our predicted 3D structure and the concept that alpha-crystallin and members of beta/gamma superfamily are structurally dissimilar.