The ribosome has an active site comprised of RNA that catalyzes peptide bond formation. To understand how RNA promotes this reaction requires a detailed understanding of the chemical transition state. Here, we report the Brønsted coefficient of the α-amino nucleophile (β nuc) using a series of puromycin derivatives. Both 50S subunit and 70S ribosome catalyzed reactions displayed linear free-energy relationships with slopes close to zero under conditions where chemistry is rate limiting. These results indicate that at the transition state the nucleophile is neutral in the ribosome catalyzed reaction, in contrast to the substantial positive charge reported for typical uncatalyzed aminolysis reactions. This suggests that the ribosomal transition state involves deprotonation to a degree commensurate with nitrogen-carbon bond formation. Such a transition state is significantly different from that of uncatalyzed aminolysis reactions in solution.

Due to the importance of allylamines in organic synthesis, the synthesis of reagents as potent precursors of aminofluoroolefins is reported from functionalized benzothiazolylsulfones. The key intermediate, a fluorovinyl sulfone, was prepared and functionalized by addition of aliphatic, aromatic amines and amino acid alkyl esters through an aza-Michael addition reaction.

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Access to fluoroalkylidene-oxetanes and -azetidines was realized from 3-oxetanone, 3-azetidinone, and fluorosulfones through the Julia-Kocienski reaction. This approach allows the preparation of new precursors of fluorinated four-mem-

A mild and reproducible method for the formation of a nonstabilized azomethine ylide was developed by photoinduced reaction catalyzed with eosin Y under green light irradiation. Resulting 1,3-dipole was trapped with fluoroalkenes, fluoroalkylated alkenes, and representative dipolarophiles to access pyrrolidine scaffolds, including spirocyclic compounds. The mechanism involved in this transformation was investigated, showing clearly a catalytic redox cycle with eosin Y.

The modified Julia olefination reaction has been applied to develop a stereoselective synthesis of fluoroalkenoate derivatives from a fluorobenzothiazolyl sulfone and aldehydes or a ketone. The olefination reaction can be achieved by using a variety of bases. DBU and DBU in the presence of MgBr2 were found to be the most efficient systems to prepare either (Z)- or (E)-alkenoates in moderate to excellent stereoselectivity.

The synthesis of new class of potential TPase inhibitors containing a difluoromethylphosphonate function as phosphate mimic is reported. This new series was prepared from a readily available fluorinated building block in few steps. Two series were evaluated as potential inhibitors: a linear series and a conformational constrained series. The activity of these multisubstrate inhibitors depends on the size of the spacer introduced between the pyrimidine ring and the phosphonate function. Best results were observed from triazolyl derivatives, easily obtained from propargylthymine and corresponding azides.

The ribosomal peptidyl transferase is a biologically essential catalyst responsible for protein synthesis. The reaction is expected to proceed through a transition state approaching tetrahedral geometry with a specific chirality. To establish that stereospecificity, we synthesized two diastereomers of a transition state inhibitor with mimics for each of the four ligands around the reactive chiral center. Preferential binding of the inhibitor that mimics a transition state with S chirality establishes the spatial position of the nascent peptide, the oxyanion and places the amine near the critical A76 2′-OH on the P-site tRNA. Another inhibitor series with 2′-NH 2 and 2′-SH substitutions at the critical 2′-OH group was used to test the neutrality of the 2′-OH as predicted if the hydroxyl functions as a proton shuttle in the transition state. Lack of significant pH dependent binding by these inhibitors argues that the 2′-OH remains neutral in the transition state. Both of these observations are consistent with a proton shuttle mechanism for the peptidyl transferase reaction.