Trivalent iodine compounds, especially, (diacetoxy) iodoarenes have been used for the formation of 1) oxygen-centered radicals from alcohols, hemi-acetals or carboxylic acids, 2) nitrogen-centered radicals from amine derivatives, and 3) carbon-centered radicals from carboxylic acids or half oxalate esters via decarboxylation. These radicals generated were employed for the Barton type reaction, β-fragmentation, oxidative addition and substitution reactions, the Hofmann-Löffier-Freytag type reaction and reductive addition reaction. Furthermore, these reactions are successfully used for the functional group transformations and for the preparation of new skeletons.
Of all options enantioselective reduction of imines is the most straightforward method for preparation of optically active amines. This asymmetric transformation can be accomplished by stoichiometric or catalytic hydroboration, aluminium hydride reduction, and, more efficiently, transition metal catalyzed reduction with organosilanes, molecular hydrogen, and formic acid. Various chiral catalysts containing Ti, Rh, Ir, and Ru have been developed for this purpose. This review summarizes the recent progress in this subject.
This article deals with the total synthesis of brefeldins and the following aspects of the synthesis are highlighted : (1) construction of the macrocyclic ring; (2) fundamental results by which the latter syntheses have been much influenced; (3) classical syntheses based on the above observations; (4) recent syntheses using stereoselective reactions; (5) syntheses based on the rearrangements and that starting with easily available compounds of multi-chiral centers; (6) synthesis of brefeldin C and 7-epi-brefeldin A.
Nucleophilic aromatic substitution (SNAr) reactions of ortho-alkoxyarylcarboxylic esters by C-, N-, and O-nucleophiles, developed in our laboratory, are reviewed. Aryl Grignard reagents efficiently displaced the 1-methoxy group of 1-methoxy-2-naphthoates to afford the corresponding biaryls in excellent yields; isopropyl ester is bulky enough to prevent the Grignard addition to the ester carbonyl function. 2-Methoxybenzoic esters derived from 2, 6-dialkylphenols also underwent the SNAr reaction by proper choice of the bulk of the 2, 6-dialkyl-substituents. High levels of asymmetric induction were achieved in these reactions by use of an enantiomeric methoxy leaving group. As the electrondonating ability of the carbanion species increased, 1, 4- or 1, 6-conjugate addition of the nucleophiles to the 2-methoxybenzoates was found to compete with the SNAr reaction. Triarylamines were conveniently prepared by the reaction of a 2- or 4-fluorobenzoate with lithium diarylamides in THF-HMPA. 2-Sulfonyl- as well as 2-phosphinoyl-substituted 1-methoxynaphthalenes also underwent the SNAr reaction. Factors affecting the activating power of the 2-substituents are discussed.
In the reaction related to NAD (P) H and its model compound, it has been reported that orientation of carbamoyl moiety in the nicotinamide ring of the coenzyme plays one of the crucial role to determine the stereochemistry of the reaction. In the oxidation of 3- (N-methyl-N-α-methylbenzylcarbamoyl) - 1, 2, 4-trimethyl-1, 4-dihydroquinoline (Me3MQPH), the stereochemistry of the product, 3- (N-methyl-N-α-methylbenzylcarbamoyl) -1, 2, 4-trimethylquinolinium ion (Me3MQP+), is influenced largely by the reactivity of the reagent employed (oxidation potential of the quinone or pKa of the amine). This interesting phenomenon has been interpreted in terms of the differences in stabilities of the two conformations concerning to the carbonyl rotation at the transition-state. The energy difference between the two conformations at the transition-state has been estimated from the temperature dependency of the product ratio. We also studied the conformational analysis of Me3MQPH, the ground-state itself, by means of the dynamic NMR technique. The contribution of the ground-state conformation and role of magnesium ion, which is used as a catalyst, are discussed.
Specific inhibitors of glycosidases are aiding in unraveling how oligosaccharides of glycoconjugates, as the functional domains for carbohydrate-protein interactions, regulate biological functions, and how they produce beneficial pharmaceutical effects in the prevention and treatment of a variety of diseases. This paper describes the progress of the synthesis of iminosugar glycosidase inhibitors, siastatin B analogues toward the rational drug design of D-glucuronic acid and L-iduronic acid-based inhibitors for tumor invasion, and of sialic acid-based inhibitors for the influenza virus sialidase, as well as indicating progress in the development of a new therapeutic and prophylactic treatment for tumor metastasis and influenza infection.