Selective Halogenation of Pyridines Using Designed Phosphine Reagents

Halopyridines are key building blocks for synthesizing pharmaceuticals, agrochemicals, and ligands for metal complexes, but strategies to selectively halogenate pyridine C-H precursors are lacking. We designed a set of heterocyclic phosphines that are installed at the 4-position of pyridines as phosphonium salts and then displaced with halide nucleophiles. A broad range of unactivated pyridines can be halogenated, and the method is viable for late-stage halogenation of complex pharmaceuticals. Computational studies indicate that C-halogen bond formation occurs via an S_NAr pathway, and phosphine elimination is the rate-determining step. Steric interactions during C-P bond cleavage account for differences in reactivity between 2- and 3-substituted pyridines.

Pyridine elaboration through organometallic intermediates: regiochemical control and completeness

Pyridines carrying heterosubstituents (such as carboxy, amido, amino, alkoxy or trifluoromethyl groups or solely individual halogen atoms) can be readily and site selectively metalated. Subsequent reaction with a suitable electrophile opens rational access to a wealth of new building blocks for the synthesis of biologically active compounds. This approach relies on organometallic methods, which are both efficacious and extremely flexible as far as the substitution site and the product structure are concerned (86 references).

4-Benzyl and 4-Benzoyl-3-dimethylaminopyridin-2(1H)-ones: In Vitro Evaluation of New C-3-Amino-Substituted and C-5,6-Alkyl-Substituted Analogues against Clinically Important HIV Mutant Strains

In a program to optimize the anti-HIV activity of the 4-benzyl and 4-benzoyl-3-dimethylaminopyridinones 9 and 10, lead compounds in a new class of highly potent non-nucleoside type inhibitors of HIV-1 reverse transcriptase, modification of the alkyl substitutents at the C-5 and C-6 positions on the pyridinone ring and of the substitutents on the C-3 amino group has been studied. Of the 17 new 5/6-modified analogues prepared, compounds 31b and 32b substituted at C-5 by an extended nonpolar chain containing an ether function and a C-6 methyl group and compound 35 bearing a C-5 ethyl/C-6 hydroxymethyl substituent pattern were selected on the basis of their in vitro activity against wild-type HIV and the three principle mutant strains, K103N, Y181C, and Y188L. When tested further, it was shown that these molecules, and in particular compound 35, are globally more active than 9, 10, and efavirenz against an additional eight single [L100I, K101E, V106A, E138K, V179E, G190A/S, and F227C] and four double HIV mutant strains [L100I + K103N, K101E + K103N, K103N + Y181C, and F227L + V106A], which are clinically relevant. Concerning modulation of the N-3 substituent, 36 new analogues were prepared. Of these, the N-methyl-N-(2-methoxyethyl)-substituted compounds 40, 42, and 62, as well as the doubly modified compounds 77a and 77b, were selected from the initial screen and were subsequently shown to be active at sub-micromolar concentrations (IC(50)'s) against all the other mutant strains except K103N + Y181C and F227L + V106A. Two possible, but distinct, modes of binding of these analogues in RT were suggested from molecular modeling studies. The preferred mode of binding for compound 62, corresponding to the predicted "orientation 1", was revealed in the X-ray crystal structure of the compound 62-RT complex.

Synthesis of an optically active, bicyclic 2-pyridone dipeptide mimetic

The eleven-step preparation of the bicyclic 2-pyridone dipeptide mimetic 1 [(3S)-6-(benzyloxycarbonylamino)-5-oxo-1,2,3,5-tetrahydroindolizine-3-carboxylic acid] in optically active form (60% ee) is described. Key steps in the synthesis of 1 include the osmium-catalyzed asymmetric dihydroxylation of olefin 13 [(6-but-3-enyl-2-methoxypyridin-3-yl)carbamic acid benzyl ester] and the intramolecular cyclization of protected diol 19 [(3'R)-[6-[4'-(tert-butyldimethylsilanyloxy)-3'-hydroxybutyl]-2-methoxypyridin-3-yl]carbamic acid benzyl ester] to afford the pyridinium salt 20 [(3S)-[3-(tert-butyldimethylsilanyloxymethyl)-5-methoxy-2,3-dihydro-1H-indolizin-6-yl]carbamic acid benzyl ester trifuoromethanesulfonic acid salt]. Several alternate methods to prepare olefin 13 are also discussed.