3,4 -Dihydroxy-2,3 -bipyridin

Only three constituents have been reported from Broussonetia zeylanica, all by a group at the University of Peradeniya in Sri Lanka [89-91]. A major alkaloid, 8-hydroxyquinoline-4-carbaldehyde (55), was identified as an antimicrobial agent active against Staphyllococus aureus and Candida albicans (the levels of activity were not specified) [89] and then two minor compounds, 3,4 -dihydroxy-2,3 -bipyridine (56) and 3,4-bis(8-hydroxyquinolin-4-yl)-y-butyrolactone (broussonetine, 57), were reported, Fig. (10) [90,91]. However, the structure of 3,4 -dihydroxy-2,3 -bipyridine (56) was revised to 8-hydroxyquinoline-4-carbaldehyde oxime (58) by synthesis [92,93]. Also, it was noted that an artefactual origin of this oxime (58) could not be ruled out due to the presence of the corresponding aldehyde (55) [93]. 

Scheme 4.1 Structure of (R)-6,6-dichloro-2, 2-dihydroxy-l,l-binaphthyl-4,4-bipyridine.

There has been considerable interest in hydroxy-3,3 -bipyridines and 3,3 -bipyridinones. Following from some very early work on the oxidation of citrazinic acid (2,6-dihydroxypyridine-4-carboxylic acid), which was considered to give some polyhydroxy-3,3 -bipyridines, it has been shown that the 3,3 -bipyridinone 59, a product of the hydrolysis of a natural blue pigment from Corynehacterium insidiosum, is obtained by oxidation of 2-hydroxy-5-aminopyridine (60) or 2,6-dihydroxypyridine-4-carboxylic acid 61) 80,83 similar oxidation of 2,6-dihydroxy-3-aminopyridine-4-carboxylic acid affords the natural product indigoidine (20). Numerous related oxidative condensations have been reported subsequently. Cyano-acetamide condensations analogous to those discussed in the synthesis of 2,3 -bipyridines afford, for example, the cyano-substituted 3,3 -bipyridinone 62 588 v, lereas condensation of 3-pyridylacetonitrile with ethyl phenyl-propiolate and ethanol affords compound 63. To complete the section on... 

Complete chlorination of 4,4 -bipyridine to octachloro-4,4 -bipyridine is accomplished by vapor-phase chlorination at 555°C. Mono-, di-, tri-, and tetrachloro-4,4 -bipyridines substituted at the positions ortho to the nitrogen atoms are obtained at lower temperatures. 2,6-Dihydroxy-3-cyano-4,4 -bipyridine gives 2,5,6-trichloro-3-cyano-4,4 -bipyridine on reaction with phosphorus chlorides, ring substitution accompanying replacement... 

Two minor alkaloids were also isolated from B. zeylanica timber. The structure of one of these, C1oN8N202, mp 223-224°C, was revised from 3,4-dihydroxy-2,2 -bipyridine (18) to 8-hydroxyquinoline-4-carbaldehyde oxime (2) based on synthetic, NMR and nuclear overhauser effect (NOE) difference NMR spectroscopic evidence (19). Natural occurrence of oximes, although rare in higher plants, is not without precedence, and the essential oil of Ruta montana L. has been reported to contain the bis-oxime of 3,4-hexanedione (20). The structure of the nonpolar minor alkaloid broussonetine, C22H16N2O4, mp 238-239°C, was elucidated as 3,4-bis(8-hydroxyquinolin-4-yl)-y-butyrolactone (4) (21). 

Recently, optodes (optical fiber chemical sensors) have been actively studied due to their inherent characteristics such as immunity to electrical noise, ease of miniaturization and the possibility of real time monitoring and remote sensing. For example, a change in absorption peak with humidity is observed using a Nafion membrane ion exchanged with dye, such as crystal violet305 or tri-phenylcarbinol.306 Similarly, a Nafion membrane loaded with the ruthenium complex [Ru(bpy)2(dhphen)]2 (bpy 2,2 -bipyridine, dhphen 4,7-dihydroxy-1,10-phenanthroline) has been used as an optical pH sensor.307... 

Phosphoryl chloride treatment of ,41-dichloro-2,2 -bipyridine 1,1-dioxide gives mainly, as expected, 4,41,6,6 -tetrachloro-2,2 -bipyridine (55) but in addition 4,4 -dichloro-3,6 -dihydroxy-2,21-bipyridine (57) is formed. The latter compound was shown to arise from hydrolysis of the intermediate isoxa.zolinium salt (56)... 

Scheme 9.23 Diamine ligands used as linkers in MOFs which also contain sites for catalysis (left) Manganeselll salen ligand, (right) dihydroxy-binaphthyl-bipyridine.

Scheme 2 Popular metal complexation motifs used for supramolecular polymer-network formation. py pyridine, bpy bipyridine, tpy terpyridine, BTP 2,6-bis(l,2,3-triazol-4-yl)pyridine, BIP 2,6-bis(l-methylbenzimidazolyl)pyridine, DOPA dihydroxy-phenylalanine, PAA poly (acrylic acid)...

BO = a-benzoinooxime BP = 2,2 -bipyridine BPH =/ /-benzoyl-/ /-phenylhydroxylamine CA = chloranilic acid DHN =2,3-dihydroxy-naphthalene DMG = dimethylglyoxime DTPA = diethylenetriaminepentaacetic acid HMMA = 4-hydroxy-2-methoxymandelic acid MA = mandelic acid NN = 1-Nitroso-2-naphthol PC = Pyrocatechol TC = 2 2 -Thiazolulazo)-p-crezol TTHA = triethylenetetramine-nehexaacetic acid. 

Dihydroxy-2,2 -bipyridine, D-80296 2 -Hydroxy-2,3 -bipyridine, H-80117 2 -Hydroxy-2,4 -bipyridine, H-80118 2-Hydroxy-3,3 -bipyridine, H-80119 2-Hydroxy-4,4 -bipyridine, H-80120 4-Hydroxy-2,2 -bipyridine, H-80121... 

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