Solid state conformations of α,β-unsaturated hydroxamates derived from the ‘chiral Weinreb amide’ auxiliary (S)-N-1-(1′-naphthyl)ethyl-O-tert-butylhydroxylamine

α,β-Unsaturated hydroxamates derived from the ‘chiral Weinreb amide’ auxiliary (S)-N-1-(1′-naphthyl)ethyl-O-tert-butylhydroxylamine consistently adopt a defined conformation and undergo highly diastereoselective conjugate addition reactions with lithium amide reagents. The configuration of the N-1-(1′-naphthyl)ethyl group dictates the position of the O-tert-butyl group and also the configuration adopted by the pyramidal nitrogen atom via a ‘chiral relay’ effect. Conjugate addition of lithium amide reagents to these substrates proceeds on the face opposite to both the O-tert-butyl group and nitrogen lone-pair with high levels of diastereoselectivity.     

α-Peptoïdes et composés apparentés : synthèse et contrôle de la conformation

The peptoid backbone derives from peptides by shifting the side chains from the Cα carbons to the adjacent amide nitrogens. This principle has been applied to β-peptides to create the β-peptoids and recently novel peptoid-type architectures were reported, such as the α,β-peptoids, arylopeptoids and N-hydroxy/alcoxy-peptoids. This account provides an overview of peptoids and related architectures both from the point of view of their synthesis as well as their conformational preferences. The most recent advances for the control of the cis/trans geometry of N,N-disubstituted peptoid amides are also outlined.     

Concise and highly selective asymmetric synthesis of acosamine from sorbic acid

Diastereoselective conjugate addition of lithium (R)-N-benzyl-N-(α-methylbenzyl)amide to tert-butyl sorbate and subsequent chemo- and diastereoselective ammonium-directed olefinic oxidation of the resultant conjugate addition product {tert-butyl (3S,αR)-3-[N-benzyl-N-(α-methylbenzyl)amino]hex-4-ene} have been used as the key steps in a concise and highly selective asymmetric synthesis of the 2,3,6-trideoxy-3-aminohexose l-acosamine. This sequence of two chemical operations allows rapid assembly of the molecular architecture and facilitates the de novo asymmetric synthesis of methyl N,O-diacetyl-α-l-acosaminide in only 7 steps from commercially available sorbic acid in 15% overall yield.     

Grafting copolymerization of vinyl monomers on polyimide macroinitiators by the method of atom transfer radical polymerization

Graft copolymers with the main polyimide chain and side chains of poly(n-butyl acrylate), poly(tert-butyl acrylate), poly(methyl methacrylate), poly(tert-butyl methacrylate), polystyrene, and polystyrene-block-poly(methyl methacrylate) were synthesized by atom transfer radical polymerization on the multicenter polyimide macroinitiators in the presence of the halide complexes of univalent copper with nitrogen-containing ligands. Polymerization of metha-crylates is most efficiently developed on the polyimide macroinitiators. The obtained graft copolymers initiate the secondary polymerization (“post-polymerization”) of methyl methacrylate. The conditions of detachment of side chains of graft polymethacrylates that do not involve the ester groups of their monomeric units were found. The molecular mass characteristics of the graft copolymers and isolated polymers, being the detached side chains of the copolymers, were determined. The detached side chains of different chemical structures have low values of the polydispersity index. The procedure developed was used for the preparation of new graft polyimides with side chains of poly-4-nitro-4′-[N-methylacryloyloxyethyl-N′-ethyl]amino-azobenzene that cause the nonlinear optical properties and with the side chains of poly(N,N-dimethylaminoethyl methacrylate) that cause the thermosensitive properties of the copolymers.     

A higher yielding synthesis of the clinical prodrug ZD2767P using di-protected 4-[N,N-bis(2-hydroxyethyl)amino]phenyl chloroformate

A novel synthesis is described of the prodrug ZD2767P (in Phase I/II clinical trials) that improves the overall yield from 13% to 45%. The method involves the synthesis of 4-[N,N-bis(2-hydroxyethyl)amino]phenyl chloroformate protected as the bis-silyl ether, coupled with di-tert-butyl glutamate. There are clear advantages of this method compared to the literature procedure.     

Asymmetric synthesis of α-mercapto-β-amino acid derivatives: application to the synthesis of polysubstituted thiomorpholines

Tandem conjugate addition of homochiral lithium N-benzyl-N-(α-methyl-p-methoxybenzyl)amide to tert-butyl cinnamate and enolate trapping with TsS^tBu proceeds with high diastereoselectivity to give a homochiral anti-α-tert-butylthio-β-amino ester. Stepwise deprotection gives the corresponding free α-tert-butylthio-β-amino acid without epimerisation. Tandem conjugate addition of homochiral lithium N-allyl-N-(α-methylbenzyl)amide to tert-butyl cinnamate and enolate trapping with TsS^tBu followed by conversion of the S-tert-butyl group to a disulphide, and reduction with Lalancette’s reagent generates polysubstituted thiomorpholine derivatives.     

Kinetics of heat-induced and photochemical transformations of quinonimines and their derivatives

Heat-induced transformations of N-[2,6-diisopropylphenyl]-3,5-di(tert-butyl)-, N-[2,6-diethylphenyl]-3,5-di(tert-butyl)-, and N-[2-methyl-6-ethylphenyl]-3,5-di(tert-butyl)-o-benzoquinonimines in nonane follow the first-order rate equation, whereas that of N-[2,5-di(tert-butyl)phenyl]-3,5-di(tert-butyl-o-benzoquinonimine obey the second-order rate equation. Kinetic parameters of these reactions have been determined. 4aH-Phenoxazine derivatives of quinonimines are intermediates of the heat-induced transformations following the first-order kinetics; under the irradiation with 405 nm light they undergo the ring opening to give the starting compounds with quantum yield close to unity.     

Convenient removal of N-tert-butyl from amides with scandium triflate

Scandium triflate has been used as a convenient and efficient catalyst for removal of N-tert-butyl from amide groups. A variety of N-tert-butyl aryl and alkyl amides under these conditions gave the corresponding primary amide in high yields. With the use of microwave heating the deprotection reaction could be completed within 1 h.     

Asymmetric synthesis of (+)-trachyspic acid

Aldol reaction of di-tert-butyl 4-(4-methoxybenzyloxy)-2-oxobutanoate with pent-4-enal using (S)-1-(3,5-bis(trifluoromethyl)phenyl)-3-(pyrrolidin-2-ylmethyl)thiourea hydrochloride as a catalyst, followed by Pinnick oxidation and tert-butyl esterification, gave (2S,3S)-di-tert-butyl 2-(2-(4-methoxybenzyloxy)ethyl)-3-allyl-2-hydroxysuccinate in high optical purity (85% ee), from which the total synthesis of (+)-trachyspic acid, a tumor cell heparanase inhibitor, was accomplished.     

Hydroxylamines and sulfinamide as amine components in the Petasis boronic acid-Mannich reaction: synthesis of N-hydroxy or alkoxy-α-aminocarboxylicacids and N-(tert-butyl sulfinyl)-α-amino carboxylicacids

An efficient synthesis of N-hydroxy or alkoxy-α-aminocarboxylic acids and N-(tert-butyl sulfinyl)-α-amino carboxylic acids has been developed from N,O-alkyl or hydroxylamines and tert-butyl sulfinamide utilizing a Petasis boronic acid-Mannich reaction. The scope and limitations of this method have been examined.     

Asymmetric synthesis of (−)-(R)-sitagliptin

The asymmetric synthesis of (?)-(R)-sitagliptin was achieved in seven steps from commercially available starting materials using the highly diastereoselective conjugate additions of either lithium (R)-N-benzyl-N-(α-methylbenzyl)amide or lithium (R)-N-benzyl-N-(α-methyl-p-methoxybenzyl)amide to tert-butyl 4-(2′,4′,5′-trifluorophenyl)but-2-enoate to install the correct stereochemistry. Subsequent sequential acid-catalysed hydrolysis of the resultant β-amino esters, HOBt/EDC mediated coupling with the triazolopyrazine fragment, and hydrogenolysis gave (?)-(R)-sitagliptin in 43% and 42% overall yields, respectively.     

New methodology for the preparation of N-tosyl aziridine-2-carboxylates

N-Tosyl aziridine-2-carboxylate methyl esters were prepared from methyl N-tosyl-l-serinate or N-tosyl-l-threoninate, tosyl chloride, and K₂CO₃, under phase-transfer catalysis (PTC) conditions. The same methodology, as applied to the tert-butyl N-tosyl-l-serine amide, afforded the corresponding newly prepared aziridine-2-carboxamide, as an enantiomerically pure compound.     

Concise,efficient and highly selective asymmetric synthesis of (+)-(3S,4R)-cisapride

A concise asymmetric synthesis of the gastroprokinetic agent (+)-(3S,4R)-cisapride {(+)-(3S,4R)-N(1)-[3′-(4″-fluorophenoxy)propyl]-3-methoxy-4-(2″′-methoxy-4″′-amino-5″′-chlorobenzamido)piperidine} from commercially available starting materials has been developed. The key step of this synthesis employs the diastereoselective conjugate addition of lithium (R)-N-benzyl-N-(α-methylbenzyl)amide to tert-butyl 5-[N-3′-(4″-fluorophenoxy)propyl-N-allylamino]pent-2-enoate and in situ enolate oxidation with (?)-camphorsulfonyloxaziridine to set the (3S,4R)-configuration found within the piperidine ring of the product. This synthesis proceeds in 9 steps from commercially available 1-(4′-fluorophenoxy)-3-bromopropane with an overall yield of 19%.     

Asymmetric synthesis of homochiral Baylis–Hillman products employing (R)-N-methyl-N-α-methylbenzyl amide

The conjugate addition of (R)-N-methyl-N-α-methylbenzyl amide to tert-butyl cinnamate followed by an asymmetric aldol reaction and subsequent N-oxidation/Cope elimination affords β-substituted homochiral Baylis–Hillman products in good yield.     

2-Amino-4-bromobutanoic Acid

(2S)- and (2R)-2-Amino-4-bromobutanoic acid were prepared starting from N-Boc-glutamic acid α tert-butyl ester. The double tert-butyl protection was necessary to prevent a partial racemisation during Barton’s radical decarboxylation used to transform the γ-carboxylic group into a bromide. This bromide reacted with different nitrogen, oxygen and sulphur nucleophiles to give nonnatural amino acids characterised by basic or heterocyclic side chains. The title compound was also used to prepare a conformationally constrained peptidomimetic.     

Total synthesis of janadolide

The first total synthesis of janadolide, a new cyclic polyketide-peptide hybrid possessing a tert-butyl group, is described. The synthesis of an unsaturated hydroxycarboxylic acid was effected via the lithiation of vinyl iodide followed by addition to a Weinreb amide with a tert-butyl group and stereoselective 1,2-reduction. The cyclic structure was constructed by macrolactamization at the amide bond between the proline moiety and fatty acid moiety.     

Solid-phase synthetic method for (±)-α-amino acids via phase-transfer catalytic alkylation

A solid supported glycineimine t-butyl ester was designed and successfully applied to the synthesis of (±)-α-amino acids. The phase-transfer catalytic alkylation, followed by acidic hydrolysis and benzoylation gave N-benzoyl-α-amino acid tert-butyl esters in high yields (up to 92%).     

Synthesis of graft copolyimides via controlled radical polymerization of methacrylates with a polyimide macroinitiator

The atom-transfer radical polymerization of methyl methacrylate and tert-butyl methacrylate with a polyimide multicenter macroinitiator in the presence of a CuCl-2,2′-bipyridine catalytic system is investigated. The kinetic features of the process, the molecular-weight characteristics of the formed side chains, and the post-polymerization of methyl methacrylate with graft polyimides containing polymethacrylate side chains are studied. The conditions of controlled polymerization yielding graft copolyimides with narrowly dispersed living poly(methyl methacrylate) or poly(tert-butyl methacrylate) side chains of variable lengths are determined.     

Convenient preparation of highly active phase-transfer catalyst for catalytic asymmetric synthesis of α-alkyl- and α,α-dialkyl-α-amino acids: application to the short asymmetric synthesis of BIRT-377

A highly active phase-transfer catalyst was conveniently prepared from the known, easily available (S)-4,5,6,4′,5′,6′-hexamethoxybiphenyldicarboxylic acid. This catalyst exhibited the high catalytic performance (0.01-1 mol %) in the asymmetric alkylation of N-(diphenylmethylene)glycine tert-butyl ester and N-(p-chlorophenylmethylene)alanine tert-butyl ester compared to the existing chiral phase-transfer catalysts, thereby allowing to realize a general and useful procedure for highly practical enantioselective synthesis of structurally diverse natural and unnatural α-alkyl-α-amino acids as well as α,α-dialkyl-α-amino acids.     

Stereospecific synthesis of differentially protected (2S,4S)-2,4-diaminoglutaric acid suitable for incorporation into peptides

The first synthesis of differentially protected (2S,4S)-2,4-diaminoglutaric acids 2 and 3 suitable for incorporation into peptides has been accomplished in a completely stereospecific manner in seven steps (overall yield 25–28%) from tert-butyl (2S,4S)-4-azido-N-tert-butoxycarbonylprolinate 5.