Protected Β-amino Acid Research Articles

Synthesis and Post-Polymerization Modification of Poly(N-(4-Vinylphenyl)Sulfonamide)s.

Herein, a straightforward synthesis of a novel class of polymers, that is, poly(N-(4-vinylphenyl)sulfonamide)s, and their monomers is reported. A set of monomers with varying electron densities, fine-tuned by different substituents on the aromatic sulfonamide moiety, is polymerized by free radical polymerization featuring low molar masses (2300≤Mn ≤3200gmol-1 ) and low dispersities (1.15≤Đ≤1.47). Further, the post-polymerization modification of the obtained polymers via aza-Michael addition with electron-deficient alkenes is demonstrated using organic superbases as catalysts, paving the way toward the facile synthesis of novel polymeric protected β-amino acid derivatives.

The kinetic resolution of oxazinones by alcoholysis: access to orthogonally protected β-amino acids.

The catalytic, alcoholytic kinetic resolution of oxazinones is reported. A novel, stereochemically dense cinchona alkaloid-based catalyst can facilitate the highly enantiodiscriminatory (S up to 101) ring-opening of oxazinones equipped with electrophilic aryl units to generate orthogonally protected β-amino acids for the first time.

Completely Stereocontrolled Aldol Reaction of Chiral β-Amino Acids

A general protocol to independently access stereoisomerically pure β'-hydroxy-β-amino acid derivatives that is based on dibutylboron triflate-mediated aldol reaction of suitably protected β-amino acids bearing chiral oxazolidinone auxiliary is reported. The method smoothly afforded syn-aldol (α,β'-syn) products in pure form and excellent isolated yield. Both α,β-syn and α,β-anti isomers are readily accessible solely through the choice of the oxazolidinone chirality. This method allows for the preparation of stereoisomeric β'-hydroxy-β-amino acid derivatives that were previously unreported.

Enantioselective gem-Chlorofluorination of Active Methylene Compounds Using a Chiral Spiro Oxazoline Ligand

Highly enantioselective gem-chlorofluorination of active methylene compounds was carried out by using a copper(II) complex of a chiral spiro pyridyl monooxazoline ligand. This reaction yielded α-chloro-α-fluoro-β-keto esters and α-chloro-α-fluoro-β-keto phosphonates with up to 92% ee. The resulting dihalo β-keto ester was converted into various α-fluoro-α-heteroatom-substituted carbonyl compounds via nucleophilic substitution without loss of optical purity. A fully protected β-amino acid with a gem-chlorofluoromethylene function was also synthesized.

Indium-mediated allylation of aldehydes, ketones and sulfonimines with 2-(alkoxy)allyl bromides

2-(Alkoxy)propenyl bromides are readily prepared from 1,3-dibromo-2-propanol in a two-step sequence involving hydroxyl protection and sodium hydride-induced dehydrobromination. Indium-mediated allylation of aldehydes, ketones, and sulfonimines with 2-(alkoxy)propenyl bromides furnishes the corresponding homoallylic alcohols and sulfonamines in good yields. The products can be easily transformed into β-hydroxy ketones and esters, as well as substituted dihydropyrans, and protected β-amino acids. Chiral 2-(alkoxy)propenyl halides, derived from (−)-menthol and d-glucal, furnish diastereomerically enriched products.

A solventless protocol for the Michael addition of aromatic amides to α,β-unsaturated esters promoted by microwave irradiation

A very simple and efficient solvent-free method for the preparation of N-benzoylated β-amino esters (protected β-amino acids) via the microwave-assisted Michael addition of aromatic amides to α,β-unsaturated esters in the presence of Cs2CO3 and tetrabutylammonium bromide (TBAB) is described. The advantages of this method are efficiency, high yields and short reaction times.

Organocatalytic Synthesis of N-Phenylisoxazolidin-5-ones and a One-Pot Synthesis of β-Amino Acid Esters

A novel N-heterocyclic carbene (NHC)-catalyzed C-N bond formation by the reaction of alpha,beta-unsaturated aldehydes and nitrosobenzene to N-phenylisoxazolidin-5-ones, followed by an acid-catalyzed esterification and Bamberger-like rearrangement in a mild one-pot protocol leads to N-p-methoxyphenyl (N-PMP) protected beta-amino acid esters.

Microwave-assisted Michael addition of sulfonamides to α,β-unsaturated esters: A rapid entry to protected β-amino acid synthesis

An efficient, clean and very simple procedure for the synthesis of protected β-amino acids is described. Michael addition of sulfonamides to α,β-unsaturated esters in the presence of K2CO3 and tetrabutylammonium bromide (TBAB) under microwave irradiation affords the title compounds in good to high yields and short reaction times. This new method affords protected β-amino acids in high yields and short reaction times.

Aggregation modes in sheets formed by protected β-amino acids and β-peptides

The crystal structures of four protected beta-amino acid residues, Boc-(S)-beta3-HAla-NHMe (1); Boc-(R)-beta3-HVal-NHMe (2); Boc-(S)-beta3-HPhe-NHMe (3); Boc-(S)-beta3-HPro-OH (6) and two beta-dipeptides, Boc-(R)-beta3-HVal-(R)-beta3-HVal-OMe (4); Boc-(R)-beta3-HVal-(S)-beta3-HVal-OMe (5) have been determined. Gauche conformations about the C(beta)-C(alpha) bonds (theta approximately +/-60 degrees) are observed for the beta3-HPhe residues in and all four beta3-HVal residues in the dipeptides and . Trans conformations (theta is approximately 180 degrees) are observed for beta3-HAla residues in both independent molecules in and for the beta3-HVal and beta3-HPro residues in and , respectively. In the cases of compounds , molecules associate in the crystals via intermolecular backbone hydrogen bonds leading to the formation of sheets. The polar strands formed by beta3-residues aggregate in both parallel (1,3,5) and antiparallel (2,4 fashion. Sheet formation accommodates both the trans and gauche conformations about the C(beta)-C(alpha) bonds.

Taveuniamides: New Chlorinated Toxins from a Mixed Assemblage of Marine Cyanobacteria.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Taveuniamides: new chlorinated toxins from a mixed assemblage of marine cyanobacteria

Brine shrimp toxicity guided fractionation of the extracts from two mixed Fijian collections of the cyanobacteria Lyngbya majuscula and Schizothrix sp. led to the isolation of eleven novel chlorinated lipids. All of these metabolites show an intriguing constellation of unsaturation (olefinic and acetylenic bonds) and chlorination at the two termini of a 15-carbon chain. The central carbon atom of the chain (C-8) is substituted in each case with an N-acetate function. Taveuniamides A–E have an adjacent carbomethoxy group at C-9 to form a protected β-amino acid while taveuniamides F–K have a methylene group at this position. A standard assortment of 2D NMR techniques in concert with mass spectrometry and other analytical techniques were used to define the structures of these novel metabolites. Taveuniamides F, G and K were the most potent brine shrimp toxins with LD 50s between 1.7–1.9 μg/mL.

Enantioselective synthesis of (+)-cryptophycin 52 (LY355703), a potent antimitotic antitumor agent.

A highly enantioselective and convergent synthesis of cryptophycin 52 (2), an exceedingly potent cytotoxic agent, is described. Cryptophycin 52, a synthetic variant of the cryptophycin family, is currently undergoing clinical trials. The synthesis is convergent and involves assembly of three fragments, phenyl hexenal 3, d-tyrosine phosphonate 4, and protected beta-amino acid derivative 5. The synthesis of fragment 3 involves an efficient and stereocontrolled construction of both stereogenic centers at C-3 and C-4 by cleavage of a substituted tetrahydrofuran ring via an acyloxycarbenium ion intermediate. Both of these stereogenic centers were derived from optically active 4-phenylbutyrolactone, synthesized enantioselectively by Corey-Bakshi-Shibata reduction.

Syntheses of Guanidinoglycosides with the Inventive use of Mitsunobu Conditions­ and 1,8-Diazabicyclo[5.4.0]undec-7-ene

A series of novel guanidinoglycosides was successfully synthesized. This was accomplished with the use of Mitsunobu conditions as a strategy to convert the glycopyranose anomeric hydroxy group to give the corresponding substituted masked guanidines in high yields. Subsequent deprotection and coupling with Fmoc protected β-amino acid, afforded a series of N,N′-substituted-methylisothioureas. Cleavage of Fmoc followed by concomitant cyclization was achieved with a catalytic amount of DBU to give the guanidinoglycosides.

Synthesis of orthogonally protected optically pure β-amino acids: Constrained phenylalanine analogs 3- tert-butoxycarbonylamino-1,2,3,4-tetrahydro-2-naphthoic acid benzyl ester

The synthesis of orthogonally protected β-amino acid 3- tert-butoxycarbonylamino-1,2,3,4-tetrahydro-2-naphthoic acid benzyl ester (Boc-βAtc-OBn) is described. The route to these constrained phenylalanine analogs features a SmI 2-mediated aziridine cleavage resulting in a β-amino ester. The stereochemistries have been determined by X-ray crystallographic analyses.

Addition of Allylmagnesium Bromide to ROPHy/SOPHy Aldoximes: Asymmetric Synthesis of Protected β-Amino Acids

A new asymmetric synthesis of protected β-amino acids is described in which the key step is the diastereoselective addition of allylmagnesium bromide to O-(1-phenylbutyl) aldoximes.

Synthesis of New Functionalized Cyclic Dipeptide

An efficient method has been developed for the synthesis of the functionalized cyclic dipeptide 6. The key step involves cyclisation of the linear dipeptide prepared by coupling a suitably protected β-amino acid with N-benzyl-t-butylglycinate.

Synthesis of α-amino acids by ring opening of aziridine-2-carboxylates with carbon nucleophiles

Excellent regiospecificity has been achieved in the reaction of carbon nucleophiles with N-para-toluenesulfonylaziridine-2-carboxylic acid (6, R = H protected as the anion. This has been developed into a general and high yielding synthesis of optically pure α-amino acids containing one chiral centre. When the aziridine (20) containing a second chiral centre was used, only lithium trimethylsilylacetylide gave the desired α-amino acid. Reaction with higher order cuprates gave lower yields, the principal products being the protected β-amino acids (22) and (23).

Addition of a Reformatsky reagent to N-anthracene-9-sulfonyl and related imines: Synthesis of protected β-amino acids

The Reformatsky reagent tert-butoxycarbonylmethylzinc bromide adds in high yields to N-sulfonylimines, e.g. 1a–1d, derived by condensation of benzaldehyde dimethyl acetal with methanesulfonamide, toluene-4-sulfonamide, 4-(methoxycarbonyl)benzenesulfonamide and sulfamide: the products are protected β-amino acids 2a–2d. N-Deprotection occurs reductively (Na-naphthalene; low yields) for 2b and 2c or hydrolytically (refluxing aq. pyridine; 76% yield of amino acid 3a after acid hydrolysis of the t-butyl ester) for the sulfamide derivatives 2d. Anthracene-9-sulfonamide ( 6) is readily available by sulfonation and chlorination of anthracene, and condenses with aldehydes [RCHO; R = Ph, 4-FC 6H 4, 4-MeOC 6H 4, 4-NCC 6H 4, 2-furyl, ( E)-styryl], e.g. in the presence of TiCl 4/Et 3N, to yield imines 7a–7f, which after addition of tert-butoxycarbonylmethylzinc bromide give protected amino acids 8a–8f; however, 8f cyclizes to the sultam 9 via a spontaneous intramolecular Diels-Alder reaction. Reductive cleavage of the N-anthracene-9-sulfonyl group is much easier than for traditional N-sulfonyl protecting groups, as demonstrated by the deprotection of 8a and 8c using aluminium amalgam.

1,4-Addition of (Diphenylmethylene)amine to Acceptor Substituted Olefins. A Versatile Synthesis of Protected β-Amino Acids, Nitriles, and Ketones

1,4-Addition of (Diphenylmethylene)amine to Acceptor Substituted Olefins. A Versatile Synthesis of Protected β-Amino Acids, Nitriles, and Ketones