Synthesis of Chiral Nitrones from N‐Fmoc Amino Acids and N‐Fmoc Dipeptides

Abstract

In this work is presented a synthetic procedure for the preparation of chiral nitrones from N‐Fmoc protected amino acids and dipeptides. The nitrone functional group can replace the carboxyl unit of amino acid and peptide systems and can be inserted into the peptide chain. The introduction of the 1,3‐dipole in peptide segments can improve the solubility and the stability toward enzymatic degradation.     

Convenient Method for Synthesis of Substituted 2‐Amino‐2‐chromenes

Some substituted 2‐amino‐2‐chromenes were synthesized by the reaction of arylidenemalononitriles with 1‐naphthol or 2‐naphthol in the presence of sodium hydroxide as catalyst under solvent‐free condition.     

Thermal Arndt–Eistert Reactions of N‐Tosyl Cyclic α‐Amino Acids

Thermal Arndt–Eistert reactions of N‐tosyl cyclic α‐amino acids were studied to explore the preparation of α,β‐unsaturated esters bearing a terminal tosylamino group. For L‐N‐tosyl‐aziridine 2‐carboxylic acid and L‐N‐tosyl‐azetidine 2‐carboxylic acid, the corresponding (E)‐α,β‐unsaturated esters were obtained stereospecifically.     

Synthesis of Monocyclic β‐Lactams via Cyclodehydration of β‐Amino Acids Using POCl3

Abstract

β‐Lactams 2 have been synthesized through a convenient use of POCl₃ via cyclodehydration of β‐amino acids 1.     

Efficient Procedure for the Preparation of Oligomer-Free N α -Fmoc Amino Acids

A two-step method is presented for the peptide-free, high-purity, and high-yield synthesis of N^α-Fmoc amino acids. The first step involves the preparation of stable dicyclohexylammonium–amino acid ionic adduct in acetone. Subsequently, the ionic adducts, on reaction with Fmoc-Nosu under mild alkaline conditions, give dipeptide-free N^α-Fmoc amino acids. The positive charge of the dicyclohexylammonium counterion in the ionic salt has a longer radius, moderating the nucleophilicity of the carboxylate ion of the amino acid and preventing by-products by arresting the formation of mixed anhydrides, the precursors of oligopeptide impurities.     

An Improved and Convenient Procedure for the Synthesis of Ozagrel

Ozagrel 1 is a 1-alkylimidazole derivative that acts as a selective inhibitor ofthromboxane A2 (TXA2) with an IC50 of 11mol/L. The beneficial effects of TXA2inhibition by ozagrel include improved motor coordination after experimental stroke, andantihypert…     

Efficient and Convenient Procedure for Preparation of N‐Sulfonylimines Catalyzed by Montmorillonite K‐10

A general and practical chemical route to the synthesis of N‐sulfonylimines using montmorillonite K‐10 as the catalyst is described. This method provides several advantages such as operational simplicity, short reaction time, using of inexpensive materials, noncorrosivity, lack of pollution, and high yields.     

A New Procedure for Highly Regio‐ and Stereoselective Iodoacetoxylation of Protected Glycals and α‐1,2‐Cyclopropanated Sugars

Protected glycals and α‐1,2‐cyclopropanated sugars were converted in high yields and selectivities in less than 2 h at low temperatures to 2‐deoxy‐2‐iodoglycosyl acetates or novel 2‐deoxy‐2‐iodomethylglycosyl acetates using the simple, inexpensive reagent mixture of ammonium iodide, hydrogen peroxide, and acetic anhydride/acetic acid in acetonitrile. The protected glycals gave rise to 2‐deoxy‐2‐bromoglycosyl acetates when ammonium bromide was used instead of the iodide, although longer reaction times were required and selectivities were inferior. Other simple olefins such as styrene and indene were also converted to their corresponding 1,2‐trans‐iodoacetates.     

A Convenient Synthesis of Protected α-Hydroxyacetaldehydes

Starting from 2, 3-O-isopropylideneglycerol (1), a general procedure for the preparation of protected α-hydroxyacetaldehydes has been developed.     

General and Facial Synthesis of 2‐Amino‐5‐halogenpyrimidine‐4‐carboxylic Acids and Their Derivatives

A facile synthetic approach to 2‐amino‐5‐halogen‐pyrimidine‐4‐carboxylic acids from 5‐halogen‐2‐methylsulfonylpyrimidine‐4‐carboxylic acid by nucleophilic displacement of the methylsulfonyl group with primary and secondary aliphatic amines has been developed. The titled amino acids underwent decarboxylation, yielding 2‐amino‐5‐halogenpyrimidines. Starting from 2‐amino‐5‐chloropyrimidine‐4‐carboxylic acid chlorides, 2‐[5‐chloro‐2‐(amino)‐4‐pyrimidinyl]‐2‐oxo‐1‐(2‐pyridyl)‐ethyl cyanides were obtained in excellent yields.     

The Synthesis of Cyclic Amino Acids

Several cyclic amino acids (1-4) were synthesized from glycine. Isocyanate ester was prepared as the key intermediate and reacted with dibromoalkanes to afford the target compounds.     

Synthesis of N‐Protected/Free Indole‐7‐Carboxaldehyde

A direct method for the preparation of N‐protected/free indole‐7‐carboxaldehyde is reported from the corresponding N‐protected 7‐bromomethylindoles using three different conditions.     

Synthesis of Novel Dendrimers Containing Amino Acids and Peptides

Dendrimers are known for their well-defined, regular, highly branched architectures with a large number of functional groups1. Recently, dendrimers have been widely researched in different fields, such as molecular light havesting, catalysts, liquid cryst…     

Reductive Amination of Glycosyl Aldoses: Synthesis of N‐Glycosylated β‐Glycosyl Amino Alcohols and their Enzyme Inhibitory Effect

Abstract

Reductive amination of glycosyl aldehydes (1a–c, 2) with glycosyl amino esters (3a–c, 4) in the presence of sodium borohydride gave diglycosylated amino esters (5–15) in good yield. N‐Glycosyl‐glycosylated amino esters were reduced to the respective diglycosyl amino alcohols (16–26) with LiAlH₄ in good yield. All the synthesized compounds were studied for their inhibitory effect, if any, against hepatic glucose‐6‐phosphatase, glycogen phosphorylase, and intestinal brush border membrane α‐glucosidase; among these compounds 7, 21, and 25 have shown marked inhibition on these enzymes, respectively.     

Rapid and Efficient Microwave‐Assisted Synthesis of N‐Carbamoyl‐L‐amino Acids

A rapid and efficient method for the synthesis of N‐carbamoyl‐L‐amino acids is reported. The procedure, involving the reaction between urea and α‐amino acids sodium salts, was performed under microwave conditions using an unmodified domestic microwave oven. A careful study of the operative conditions indicated proline (1d) as the less reactive substrate and phenylglycine (1e) as the more reactive one among all the α‐amino acids tested. Substitution of urea with potassium cyanate produced a low conversion into the corresponding N‐carbamoyl derivative, and a possible explanation of this result is reported.     

Enantioselective Synthesis of (R)‐2‐Methylalkanoic Acids: A Convenient Approach to α‐Substituted Chiral Carboxylic Acid Derivatives

Abstract

Racemization‐free deacylation of N‐acylimidazolidine‐2‐ones using lithium hydroperoxide affords the corresponding α‐substituted chiral carboxylic acids in high yield while permitting recovery of the chiral auxiliary.     

Convenient Asymmetric Borane Reduction of Ketones Catalyzed by Simple Amino Alcohols and Corresponding Amino Acids

The catalytic enantioselective borane reduction of ketones is a well-studied theme1. Since the pioneering work of Corey2, a variety of good catalysts have been synthesized through further modification on simple amino alcohols and their corresponding amino acids,3,4 . But when simple amino alcohols were directly used in the reduction their catalytic efficiency was very low. For the first time Buono5 has reported through carefully chosen reaction condition the catalytic efficiency of a simple…     

Synthesis of Fully Protected N‐Arylglycosylamines and Factors Affecting the Configuration of C1‐Substituents of N‐Arylglycosylamines

Abstract

An efficient method was reported for preparation of N‐arylglycosylamines in aqueous THF under reflux in good yields. The factors affecting the configuration of C₁‐substituents of N‐aryglycosylamines was investigated, that is, the influence of solvents, substituents of aromatic amines, and protecting groups of monosaccharides on the ratio of α‐ and β‐N‐arylglycosylamines.     

A Convenient Procedure for the Synthesis of 6-O-Mono-Phosphate β-Cyclodextrins

Abstract

The synthesis of β-cyclodextrin derivatives bearing one phosphate group on the primary rim is reported. These compounds were prepared in good to excellent yields, by reacting β-cyclodextrin with dialkyl chlorophosphates in the presence of 4-dimethyl amino pyridine (DMAP) catalyst and dimethylformamide (DMF) as solvent. The methodology described is highly selective and the purification of the title compounds is simple, because difficulties due to phosphate regioisomers mixture are avoided.     

New One‐Pot Three‐Component Synthesis of N‐Phenyl α‐Aminophosphonates

New one‐pot three‐component reactions employing aldehydes, triphenylphosphite, and N‐[(phenylamino)carbonyl]glycine ethyl ester in refluxing xylene readily afford N‐phenyl α‐aminophosphonates in low to moderate yields.