α-Pyridinyl Alcohols, α,α'-Pyridine Diols, α-Bipyridinyl Alcohols, and α,α'-Bipyridine Diols as Structure Motifs Towards Important Organic Molecules and Transition Metal Complexes.

BACKGROUND: The preparation and use of pyridinyl alcohols as ligands showed incredible increment in the past three decades. Important property of pyridinyl alcoholato ligands is their strong basicity, which is mainly due to the lack of resonance stabilization of the corresponding anion. This strongly basic anionic nature gives them high ability to make bridges between metal centers rather than to bind to only one metal center in a terminal fashion. They are needed as ligands due to their ability to interact with transition metals both covalently (with oxygen) and hemilabile coordination (through nitrogen). OBJECTIVE: The review focuses on the wide application of α-pyridinyl alcohols, α,α'-pyridine diols, α- bipyridinyl alcohols, and α,α'-bipyridine diols as structure motifs in the preparation of important organic molecules which is due to their strongly basic anionic nature. CONCLUSION: It is clear from the review that in addition to their synthetic utility in the homogeneous and asymmetric catalytic reactions, the preparation of the crown ethers, cyclic and acyclic ethers, coordinated borates (boronic esters), pyridinyl-phosphine ligands, pyridinyl-phosphite ligands, and pyridinyl-phosphinite ligands is the other broad area of application of pyridinyl alcohols. In addition to the aforementioned applications they are used for modeling mode of action of enzymes and some therapeutic agents. Their strongly basic anionic nature gives them high ability to make bridges between metal centers rather than to bind to only one metal center in a terminal fashion in the synthesis of transition metal cluster complexes. Not least numbers of single molecule magnets that can be used as storage of high density information were the result of transition metal complexes of pyridinyl alcoholato ligands.

Synthesis and evaluation of chromone derivatives as inhibitors of monoamine oxidase.

Based on reports that chromone compounds are good potency inhibitors of monoamine oxidase (MAO), the present study evaluates the effect of substitution with flexible side chains on the 3 position on MAO inhibition potency. Fifteen chromone derivatives were synthesised by reacting aromatic and aliphatic amines and alcohols with chromone 3-carboxylic acid in the presence of carbonyldiimidazole (CDI). This yielded chromane-2,4-dione and ester chromone derivatives. Generally, the esters exhibited weak MAO inhibition, while the chromane-2,4-dione derivatives showed promise as selective MAO-B inhibitors with IC50 values in the micromolar range. Compound 14b, 3-[(benzylamino)methylidene]-3,4-dihydro-2H-1-benzopyran-2,4-dione, was the most potent MAO-B inhibitor with an IC50 value of 638 µM. This compound was shown to be a reversible and competitive MAO-B inhibitor with a Ki of 94 µM. In conclusion, the effect of chain elongation and introduction of flexible substituents on position 3 of chromone were explored and the results showed that aminomethylidene substitution is preferable over ester substitution. Good potency MAO-B inhibitors may act as leads for the design and development of therapy for Parkinson's disease where these agents reduce the central metabolism of dopamine.

Improved metathesis lifetime: chelating pyridinyl-alcoholato ligands in the second generation Grubbs precatalyst.

Hemilabile ligands can release a free coordination site "on demand" of an incoming nucleophilic substrate while occupying it otherwise. This is believed to increase the thermal stability and activity of catalytic systems and therefore prevent decomposition via free coordination sites. In this investigation chelating pyridinyl-alcoholato ligands were identified as possible hemilabile ligands for incorporation into the second generation Grubbs precatalyst. The O,N-alcoholato ligands with different steric bulk could be successfully incorporated into the precatalysts. The incorporation of the sterically hindered, hemilabile O,N-ligands improved the thermal stability, activity, selectivity and lifetime of these complexes towards the metathesis of 1-octene. A decrease in the activity of the second generation Grubbs precatalyst was additionally observed after incorporating a hemilabile O,N-ligand with two phenyl groups into the system, while increasing their lifetime.