The conjugate addition of enantiomerically pure lithium amides as homochiral ammonia equivalents: scope, limitations and synthetic applications

General entry to asymmetric one-pot [N + 2 + n] cyclization for the synthesis of three- to seven-membered azacycloalkanes

Enantio- and diastereoselective one-pot synthesis of three- to seven-membered cis-azaheterocycles was achieved using a triggered asymmetric conjugate addition reaction of lithium amide with an enoate, followed by alkylation of the resulting lithium enolate with α,ω-dihaloalkane and N-alkylation. Isomerization of cis-azaheterocycles with a base yielded the trans-product, constituting a one-pot synthesis of cis-azacycles and a two-step synthesis of trans-azacycles. The four-step asymmetric synthesis of nemonapride highlights the general utility of the method.

Ammonium-directed olefinic epoxidation: kinetic and mechanistic insights

The ammonium-directed olefinic epoxidations of a range of differentially N-substituted cyclic allylic and homoallylic amines (derived from cyclopentene, cyclohexene, and cycloheptene) have been investigated, and the reaction kinetics have been analyzed. The results of these studies suggest that both the ring size and the identity of the substituents on nitrogen are important in determining both the overall rate and the stereochemical outcome of the epoxidation reaction. In general, secondary amines or tertiary amines with nonsterically demanding substituents on nitrogen are superior to tertiary amines with sterically demanding substituents on nitrogen in their ability to promote the oxidation reaction. Furthermore, in all cases examined, the ability of the (in situ formed) ammonium substituent to direct the stereochemical course of the epoxidation reaction is either comparable or superior to that of the analogous hydroxyl substituent. Much slower rates of ring-opening of the intermediate epoxides are observed in cyclopentene-derived and cycloheptene-derived allylic amines as compared with their cyclohexene-derived allylic and homoallylic amine counterparts, allowing for isolation of these intermediates in both of the former cases.

Design and synthesis of a bivalent ligand to explore the putative heterodimerization of the mu opioid receptor and the chemokine receptor CCR5

The bivalent ligand approach has been utilized not only to study the underlying mechanism of G protein-coupled receptors dimerization and/or oligomerization, but also to enhance ligand affinity and/or selectivity for potential treatment of a variety of diseases by targeting this process. Substance abuse and addiction have made both the prevention and the treatment of human immunodeficiency virus (HIV) infection more difficult to tackle. Morphine, a mu opioid receptor (MOR) agonist, can accelerate HIV infection through up-regulating the expression of the chemokine receptor CCR5, a well-known co-receptor for HIV invasion to the host cells and this has been extensively studied. Meanwhile, two research groups have described the putative MOR-CCR5 heterodimers in their independent studies. The purpose of this paper is to report the design and synthesis of a bivalent ligand to explore the biological and pharmacological process of the putative MOR-CCR5 dimerization phenomenon. The developed bivalent ligand thus contains two distinct pharmacophores linked through a spacer; ideally one of which will interact with the MOR and the other with the CCR5. Naltrexone and Maraviroc were selected as the pharmacophores to generate such a bivalent probe. The overall reaction route to prepare this bivalent ligand was convergent and efficient, and involved sixteen steps with moderate to good yields. The preliminary biological characterization showed that the bivalent compound 1 retained the pharmacological characteristics of both pharmacophores towards the MOR and the CCR5 respectively with relatively lower binding affinity, which tentatively validated our original molecular design.

(3S*,4S*,E)-tert-Butyl 3,4-dibromo-5-oxocyclooct-1-enecarboxylate

The title compound, C₁₃H₁₈Br₂O₃, was prepared by a bromination reaction of (1E,3Z)-methyl 5-oxocyclo­octa-1,3-diene­carboxyl­ate, which was obtained by an ep­oxy­dation reaction of tert-butyl cyclo­oct-1,3-diene­carboxyl­ate. The crystal structure confirms unequivocally the absolute configuration of both chiral centres to be S. In the crystal, C—H⋯O inter­actions link the mol­ecules into chains running along the c axis.

Parallel kinetic resolution of acyclic γ-amino-α,β-unsaturated esters: application to the asymmetric synthesis of 4-aminopyrrolidin-2-ones

Conjugate addition of a 50:50 pseudoenantiomeric mixture of lithium (R)-N-benzyl-N-(α-methylbenzyl)amide and lithium (S)-N-3,4-dimethoxybenzyl-N-(α-methylbenzyl)amide to a range of racemic acyclic γ-amino-α,β-unsaturated esters (derived from the corresponding α-amino acids) effects their efficient parallel kinetic resolution, allowing the preparation of enantiopure β,γ-diamino esters. The β,γ-diamino ester products of these reactions are readily converted into the corresponding substituted 4-aminopyrrolidin-2-ones via N-debenzylation and cyclization.

Enantioselective synthesis of α-fluoro-β(3)-amino esters: synthesis of enantiopure, orthogonally protected α-fluoro-β(3)-lysine

The scope of a tandem conjugate addition-fluorination sequence performed on α,β-unsaturated esters using the enantiopure lithium amide derived from (S)-N-benzyl-N-(α-methylbenzyl)amine, and the electrophilic fluorinating agent N-fluorobenzenesulfonimide has been investigated. Using this method, α-fluoro-β(3)-amino esters can be obtained in up to quantitative yield and 80:20 to >99:1 dr. This simple methodology does not rely on the use of α-amino acids from the chiral pool and thus provides the potential for the preparation of enantiopure α-fluoro-β(3)-amino acids with a wide variety of side chains. Its utility was demonstrated through the synthesis of orthogonally protected (2S,3S)-α-fluoro-β(3)-lysine.

1,4-addition of lithium diisopropylamide to unsaturated esters: role of rate-limiting deaggregation, autocatalysis, lithium chloride catalysis, and other mixed aggregation effects

Lithium diisopropylamide (LDA) in tetrahydrofuran at -78 °C undergoes 1,4-addition to an unsaturated ester via a rate-limiting deaggregation of LDA dimer followed by a post-rate-limiting reaction with the substrate. Muted autocatalysis is traced to a lithium enolate-mediated deaggregation of the LDA dimer and the intervention of LDA-lithium enolate mixed aggregates displaying higher reactivities than LDA. Striking accelerations are elicited by <1.0 mol % LiCl. Rate and mechanistic studies have revealed that the uncatalyzed and catalyzed pathways funnel through a common monosolvated-monomer-based intermediate. Four distinct classes of mixed aggregation effects are discussed.

Highly (E)-selective Wadsworth-Emmons reactions promoted by methylmagnesium bromide

An experimentally simple protocol for the very highly (E)-selective Wadsworth-Emmons reaction [(E):(Z) selectivities in excess of 180:1 in some cases] of a range of straight-chain and branched aliphatic, substituted aromatic, and base-sensitive aldehydes via reaction with an alkyl diethylphosphonoacetate and MeMgBr is reported.

N-sulfinyl amines as a nitrogen source in the asymmetric intramolecular aza-Michael reaction: total synthesis of (-)-pinidinol

N-Sulfinyl amines have been successfully employed as nitrogen nucleophiles for the asymmetric intramolecular aza-Michael reaction. The synthetic strategy involves a cross-metathesis reaction followed by the Michael-type cyclization, either in a base-catalyzed two-step procedure or in a tandem fashion. The developed methodology allows access to chiral substituted pyrrolidines and piperidines bearing one or two stereocenters and it has been applied to the synthesis of the piperidine alkaloid (-)-pinidinol.