Stereoselective synthesis of a terpyrrolidine unit, a potential building block for anion recognition

Reactions of Allylmagnesium Reagents with Carbonyl Compounds and Compounds with C═N Double Bonds: Their Diastereoselectivities Generally Cannot Be Analyzed Using the Felkin-Anh and Chelation-Control Models

This review describes the additions of allylmagnesium reagents to carbonyl compounds and to imines, focusing on the differences in reactivity between allylmagnesium halides and other Grignard reagents. In many cases, allylmagnesium reagents either react with low stereoselectivity when other Grignard reagents react with high selectivity, or allylmagnesium reagents react with the opposite stereoselectivity. This review collects hundreds of examples, discusses the origins of stereoselectivities or the lack of stereoselectivity, and evaluates why selectivity may not occur and when it will likely occur.

Conformational landscape of substituted prolines

The cyclic side chain of the amino acid proline confers unique conformational restraints on its backbone and side chain dihedral angles. This affects two equilibria-one at the backbone (cis/trans) and the other at the side chain (endo/exo). Substitutions on the proline ring impose additional steric and stereoelectronic effects that can further modulate both these equilibria, which in turn can also affect the backbone dihedral angle (ϕ, ψ) preferences. In this review, we have explored the conformational landscape of several termini capped mono-(2-, 3-, 4-, and 5-) substituted proline derivatives in the Cambridge Structural Database, correlating observed conformations with the nature of substituents and deciphering the underlying interactions for the observed structural biases. The impact of incorporating these derivatives within model peptides and proteins are also discussed for selected cases. Several of these substituents have been used to introduce bioorthogonal functionality and modulate structure-specific ligand recognition or used as spectroscopic probes. The incorporation of these diversely applicable functional groups, coupled with their ability to define an amino acid conformation via stereoelectronic effects, have a broad appeal among chemical biologists, molecular biophysicists, and medicinal chemists.

Toward Improving the Chemistry of N-Acyliminium Ions: Nucleophilic Substitution Reactions of Pyrrolidinone Derivatives with Trialkylsilyl Nucleophiles Catalyzed by Triisopropylsilyltrifluoromethane Sulfonate (TIPSOTf)

[reaction: see text] Nucleophilic substitution reactions of racemic and chiral 5-acetoxy-, 5-ethoxy-, and 5-methoxypyrrolidin-2-ones by silicon-based nucleophiles were efficiently catalyzed by TIPSOTf. This process was found to be general and accommodates a broad range of substrate-nucleophile combinations.

Total synthesis of desferrisalmycin B

The first total synthesis of a naturally occurring siderophore antibiotic, desferrisalmycin B, is described, and the configuration of the unknown stereocenter is assigned. The synthesis features a synthetic strategy of constructing the novel amino-heptopyranoside component by stereoselective dihydroxylation followed by a Bose-modified Mitsunobu reaction. Through this convergent approach, other members of salmycins should also be synthetically accessible.

Total synthesis of A-315675: a potent inhibitor of influenza neuraminidase

A concise, stereocontrolled, and practical synthesis of a neuraminidase inhibitor consisting of a highly functionalized D-proline scaffold is described. Key features involve a stereocontrolled addition of a propiolate ester to a chiral nonracemic nitrone derived originally from D-serine and the manipulation of acyclic and cyclic motifs en route to the target in 12.8% overall yield over 22 steps. Several crystalline intermediates were suitable for single-crystal X-ray analysis.