10.1021/jo952083l
The research focuses on the synthesis of the C1-C21 fragment of the serine/threonine phosphatase inhibitor tautomycin, a novel secondary metabolite with significant biological activity. The purpose of this study was to develop a synthetic route to this complex natural product, which could potentially lead to the development of new therapeutic agents. The researchers successfully synthesized compound 40, which contains the C1-C21 region of tautomycin, using a series of chemical reactions that included the Matteson’s chloromethylene insertion reaction to construct stereocenters and Cr/Ni-mediated coupling to form the spirocyclic structure. Key chemicals used in the synthesis process included various organometallic reagents, protecting groups like PMB (para-methoxybenzyl), and reagents for oxidation and reduction steps such as DDQ (2,3-dichloro-5,6-dicyano-1,4-benzoquinone) and lithium aluminum hydride. The conclusions of the research detailed the successful synthesis of the target fragment with a high degree of stereoselectivity, setting the stage for further extension to the natural product tautomycin and potential applications in the study of serine/threonine phosphatases.
10.1002/hlca.200690010
The research explores a synthetic method for converting amino acids into chiral 1-(heteroaryl)ethanamines and 1-(heteroaryl)-1-aminopropan-2-ols using enamino ketones as key intermediates. The study aims to develop an efficient and versatile synthetic route for these compounds, which are important in various applications such as chiral catalysts and resolving agents. The methodology involves transforming N-protected L-phenylalanines and L-threonine into chiral enamino ketones via Weinreb amides and ethynyl ketones. These enamino ketones are then reacted with various heterocyclic compounds like pyrazolamines and hydrazine derivatives to form the desired products. The final deprotection step yields the free amines. The research concludes that this enamino ketone methodology is a useful and efficient approach for synthesizing chiral nonracemic 1-(heteroaryl)alkanamines, offering advantages over some existing methods. Key chemicals used include N-protected L-phenylalanines, L-threonine, Weinreb amides, ethynylmagnesium bromide, and various heterocyclic reagents such as pyrazolamines and hydrazine derivatives.
10.1246/bcsj.54.1844
The study investigates the synthesis of oxazolidines, thiazolidines, and 5,6,7,8-tetrahydro-1H,3H-pyrrolo[1,2-c]oxazole (or thiazole)-1,3-diones from β-hydroxy- or β-mercapto-α-amino acid esters. Aromatic aldehydes such as benzaldehyde, p-anisaldehyde, p-chlorobenzaldehyde, and p-nitrobenzaldehyde are used to react with amino acid ethyl esters like L-serine, 3-phenyl-DL-serine, L-threonine, or L-cysteine to form oxazolidines or thiazolidines. These compounds can then be converted into oxazoles and thiazoles through dehydrogenation using N-bromosuccinimide. Acetylation of oxazolidines and thiazolidines leads to N-acetylderivatives, which can undergo cyclization in the presence of anhydrous ZnCl? to form the tetrahydro-pyrrolo[1,2-c]oxazole (or thiazole)-1,3-diones. The study also explores the interaction of oxazolidines and thiazolidines with p-nitrobenzaldehyde and piperidine to form Mannich bases. The IR spectra of the synthesized compounds are analyzed, showing characteristic shifts and absorptions related to functional groups such as the ester group and the oxazole or thiazole ring.
10.1002/hlca.19870700426
The study, titled "Stereoselective Alkylation at C(α) of Serine, Glyceric Acid, Threonine, and Tartaric Acid Involving Heterocyclic Enolates with Exocyclic Double Bonds," investigates the stereoselective alkylation of various chiral, non-racemic α-amino acids and their derivatives using heterocyclic enolates with exocyclic double bonds. The researchers converted these acids into methyl dioxolane, oxazoline, and oxazolidine carboxylates. These compounds were then deprotonated to form lithium enolates, which were stable enough to undergo alkylation with or without cosolvents like HMPA or DMPU. The products were obtained in good to excellent yields and with high diastereoselectivities, except for the tartrate-derived acetonide. The study demonstrated that the configuration of the products could be determined through NOE-NMR measurements and chemical correlation, revealing that the dioxolane-derived enolates were alkylated preferentially from the face already substituted, while the dihydrooxazol- and oxazolidine-derived enolates were alkylated from the opposite face. This work provides a method for constructing quaternary stereogenic centers without racemization, using readily available enantiomerically pure precursors like hydroxy- and amino-acids.
10.1016/j.tet.2018.04.082
The study presents a simplified method for beta-glycosylation of peptides, focusing on the activation of S-phenyl thioglycosides using N-iodosuccinimide and catalytic copper(I) triflate. This method effectively promotes beta-O-glycosylation at serine and threonine hydroxyls in "mono-," di-, and tripeptides, as well as beta-N-glycosylation of asparagine-containing peptides. A key advantage is the minimization of undesired amide O-glycosylation. The study also develops streamlined deprotection sequences based on global hydrogenolysis, leading to the parent glycopeptides. The core glycopeptide region for biological protein N-glycosylation has been synthesized, purified, and characterized. The research provides an efficient process for O- and N-glycosylation of peptides, which is beneficial for multistep preparations, especially those limited by material availability.
10.1080/00397910903051259
The research explores the synthesis of N-phenyl methyl esters of various amino acids using diphenyliodonium bromide as a key reagent. The study focuses on the efficient and selective N-phenylation of α-amino acids, including glycine, alanine, valine, leucine, isoleucine, phenylalanine, methionine, proline, serine, threonine, tyrosine, aspartic acid, and glutamic acid. The process involves converting the amino acids into their methyl ester hydrochloride salts, followed by neutralization to obtain free amines. These amines are then subjected to N-phenylation in the presence of diphenyliodonium bromide, silver nitrate, and a catalytic amount of copper bromide. The chiral integrity of the amino acids is maintained throughout the reactions, as confirmed by the synthesis of dipeptides for each N-phenyl amino acid. The structures of the new compounds are characterized using IR, 1H, and 13C NMR spectroscopy, as well as CHN microanalysis or high-resolution mass spectrometry. The study highlights the utility of diphenyliodonium bromide in the synthesis of N-phenylated amino acids, demonstrating good to excellent yields and maintaining the chirality of the starting amino acids.
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