Regioselective Synthesis of Aniline-Derived 1,3- and Ci-Symmetric 1,4-Diols from trans-1,4-Cyclohexadiene Dioxide

An Operationally Simple Approach to Indole Derivatives from 2-Alkenylanilines Utilizing an Oxidation-Intramolecular Cyclization-Elimination Sequence

Herein we describe a novel route to indole derivatives from a variety of N-substituted 2-alkenylanilines. This route features three operationally simple steps: (1) oxidation to convert N-substituted 2-alkenylanilines into epoxide intermediates, (2) intramolecular cyclization, and (3) the acid-catalyzed elimination of water.

Concise syntheses and some biological activities of dl-2,5-di-O-methyl-chiro-inositol, dl-1,4-di-O-methyl-scyllo-inositol, and dl-1,6-dibromo-1,6-dideoxy-2,5-di-O-methyl-chiro-inositol

The regio- and stereospecific synthesis of O-methyl-chiro-inositols and O-methyl-scyllo-inositol was achieved, starting from p-benzoquinone. After preparing dimethoxy conduritol-B as a key compound, regiospecific bromination of the alkene moiety of dimethoxy conduritol-B and acid-catalyzed ring opening of dimethoxydiacetate conduritol-B epoxide with Ac₂ O afforded the desired new chiro-inositol derivatives and scyllo-inositol derivative, respectively. Spectroscopic methods were employed for the characterization of all synthesized compounds. The novel inositols (11-17) had effective inhibition profiles against human carbonic anhydrase isoenzymes I and II (hCA I and II) and acetylcholinesterase (AChE). The novel inositols 11-17 were found to be effective inhibitors against AChE, hCA I, and hCA II enzymes. K_i values were calculated in the range of 87.59 ± 7.011 to 237.95 ± 17.75 μM for hCA I, 65.08 ± 12.39 to 538.98 ± 61.26 μM for hCA II, and 193.28 ± 43.13 to 765.08 ± 209.77 μM for AChE, respectively. Also, due to the inhibitory effects of the novel inositols 11-17 against the tested enzymes, these novel inositols are potential drug candidates to treat some diseases such as glaucoma, epilepsy, leukemia, and Alzheimer's disease.

A computational study of regioselectivity in aluminum hydride ring-opening of cis- and trans-4-t-butyl and 3-methylcyclohexene oxides

Nucleophilic ring opening of cyclohexene oxides is known to proceed preferentially through the trans-diaxial pathway (the Fürst-Plattner rule). This preference, however, is not absolute, and can be affected by substituents on the cyclohexene oxide ring, as illustrated by LiAlH4 ring-opening of the cis- and trans-isomers of 4-t-butyl- and 3-methylcyclohexene oxide (cis- and trans-1, cis- and trans-2). We performed B3LYP/6-31+G*(PCM) geometry optimizations to locate the chair-like and twist-boat-like transition structures for the hydride attacks on the pseudoaxial and pseudoequatorial conformers of these epoxides. Our calculations are consistent with the experimental observation of effective Fürst-Plattner control of AlH4--opening of cis-1, trans-1, and cis-2, but low selectivity in ring-opening of trans-2. Our data at B3LYP/6-31+G*(PCM) suggests this reduction in selectivity is due to a diminished pseudoequatorial preference of the 3-methyl group in trans-2 relative to that in cis-2. The two calculated chair-like transition structures for hydride opening of trans-2 differ in activation energy free energy (ΔΔG‡) by only 0.4 kcal mol-1. Thus, these calculations account for the reduced regioselectivity of ring opening seen for trans-2 by AlH4- and other nucleophiles.

Conformation-induced regioselective and divergent opening of epoxides by fluoride: facile access to hydroxylated fluoro-piperidines

Utilizing molecular conformation as a controlling factor, epoxide-containing 2-aryl-piperidines can be ring-opened with the reagent combination of tetrabutylammonium fluoride (TBAF) and potassium bifluoride (KHF2) in a regioselective and divergent fashion. Four different types of hydroxylated fluoro-piperidines, valuable building blocks in drug development, were readily synthesized using this method. The basic nature of the reagent combination allowed a one-pot deprotection/ring opening process, which increased the efficacy of this transformation.

Triazole-linked reduced amide isosteres: an approach for the fragment-based drug discovery of anti-Alzheimer's BACE1 inhibitors

In the course of a β-site APP-cleaving enzyme 1 (BACE1) inhibitor discovery project an in situ synthesis/screening protocol was employed to prepare 120 triazole-linked reduced amide isostere inhibitors. Among these compounds, four showed modest (single digit micromolar) BACE1 inhibition. Our ligand design was based on a potent reduced amide isostere 1, wherein the P(2) amide moiety was replaced with an anti-1,2,3-triazole unit. Unfortunately, this replacement resulted in a 1000-fold decrease in potency. Docking studies of triazole-linked reduced amide isostere A3Z10 and potent oxadiazole-linked tertiary carbinamine 2a with BACE1 suggests that the docking poses of A3Z10 and 2a in the active sites are quite similar, with one exception. In the docked structures the placement of the protonated amine that engages D228 differs considerably between 2a and A3Z10. This difference could account for the lower BACE1 inhibition potency of A3Z10 and related compounds relative to 2a.

1,3-allylic strain as a strategic diversification element for constructing libraries of substituted 2-arylpiperidines

Flipping diversity

Minimization of 1,3-allylic strain is a recurring element in the design of a stereochemically- and spatially-diverse collection of 2-arylpiperidines. Here, stereochemically-diverse scaffolding is first constructed using A1,3 strain to guide the regioselective addition of nucleophiles, which serve as handles for further substitution. N -substitution with alkyl and acyl substituents again leverages A1,3 strain to direct each stereoisomer to two different conformer populations, doubling the number of library members.