Picolinic add

Related to amino acids is picolinic add (8), which is present at high concentrations in dormant tissues such as plant seeds and whose involvement in the quiescent state may involve iron chelation. Also mugineic acid (9) possesses strong Fe111 chelating properties. This amino acid derivative has been isolated from the roots of rice plants and has been found to have a strong stimulatory effect on Fe uptake. The crystal structure of a complex of Co111 shows that the anion of (9) can function as a hexadentate chelate.38... 

Complexes of pyridine-2-carboxylic acid (picolinic add, picH) and its substituted derivatives commonly exhibit the N—O bidentate nature of this aromatic amino add. From aqueous solutions chelates are obtained with the coordinated carboxylic group deprotonated, or neutral ligand forms may be isolated from non-aqueous media. Bis chelates are common in either case with bivalent metal ions. The tris chelates of trivalent cobalt and manganese have been structurally characterized recently. The latter is tetragonally distorted in a structure similar to Mn (oxine)j. 

Wu, K.J., Steding, A., and Becker, C.H. (1993) Matrix-assisted laser desorption time-of-flight mass spectrometry of oligonudeotides using 3-hydroj picolinic add as an ultraviolet-... 

Picolinic Add Metabolism. Picolinic acid is converted to its glycine conjugate when administered to mammals. - Birds use ornithine in place of glycine. The mechanism of the condensation is not known, but presumably it resembles the formation of hippuric acid, in which a CoA derivative of the carboxyl group is the acylating agent. A-Methylpicolinic... 

Figure 2. Calibration curves for the determination of mercury with electrodes modified with tryptophan, 6-aminohexanoic acid and picolinic add.

Reactions with Ammonia and Amines. Acetaldehyde readily adds ammonia to form acetaldehyde—ammonia. Diethyl amine [109-87-7] is obtained when acetaldehyde is added to a saturated aqueous or alcohoHc solution of ammonia and the mixture is heated to 50—75°C in the presence of a nickel catalyst and hydrogen at 1.2 MPa (12 atm). Pyridine [110-86-1] and pyridine derivatives are made from paraldehyde and aqueous ammonia in the presence of a catalyst at elevated temperatures (62) acetaldehyde may also be used but the yields of pyridine are generally lower than when paraldehyde is the starting material. The vapor-phase reaction of formaldehyde, acetaldehyde, and ammonia at 360°C over oxide catalyst was studied a 49% yield of pyridine and picolines was obtained using an activated siHca—alumina catalyst (63). Brown polymers result when acetaldehyde reacts with ammonia or amines at a pH of 6—7 and temperature of 3—25°C (64). Primary amines and acetaldehyde condense to give Schiff bases CH2CH=NR. The Schiff base reverts to the starting materials in the presence of acids. 

Scheme 12 Total synthesis of (-)-xestospongin A (116), (+)-araguspongine B (129), and (+)-xestospongin C (130) [41]. Experimental conditions i. (a) NaH, THE, (b) -BuLi, (c) 132 a. Ru(II)-S-BINAP, H2, EtOH Hi. LiBH4, Et20 iv. PPTS, 2,2-dimethoxypropane, acetone v. Nal, acetone, reflux vi. 3-picoline, EDA, THE vii. HCl(aq.), EtOH viii. TsCl, EtsN, CH2CI2 ix. Nal, butanone, reflux x. LiBH4, MeOH, i-PrOH xi. DEAD, CH2CI2 xii. H2, Ni (Raney), MeOH xiii. Rh on alumina, MeOH, H2, then add alumina, reflux...

Another example illustrating the greater reactivity of organolithium compounds is the preparation of the otherwise difficultly accessible esters of 2-pyridyI-scetic add by the following series of reactions from a-picoline ... 

Optimized reaction conditions call for the use of Wilkinson s catalyst in conjunction with the organocatalyst 2-amino-3-picoline (60) and a Br0nsted add. Jun and coworkers have demonstrated the effectiveness of this catalyst mixture for a number of reactions induding hydroacylation and C—H bond fundionalization [25]. Whereas, in most cases, the Lewis basic pyridyl nitrogen of the cocatalyst ads to dired the insertion of rhodium into a bond of interest, in this case the opposite is true - the pyridyl nitrogen direds the attack of cocatalyst onto an organorhodium spedes (Scheme 9.11). Hydroamination of the vinylidene complex 61 by 3-amino-2-picoline gives the chelated amino-carbene complex 62, which is in equilibrium with a-bound hydrido-rhodium tautomers 63 and 64. 

Picolinate-N-oxido anion (PICO), transition metal peroxides, 1058, 1095 Picolinic acid (pic), transition metal peroxides, 1054, 1058, 1067, 1076 (—)-/3-Pinene, artemisinin synthesis, 288, 289 Plakorin, 191, 247, 1333 Plakortic add, 190, 191 Plakortin, 190, 191... 

The carbamic adds may catalyse the polymerisation, and indeed, in the polymerisation of sarcosine NCA the catalytic effect of weak carboxylic adds, such as a-picolinic, was demonstrated (20). The polymerisation becomes inhibited, however, at high acid concentration, or on addition of a strong add such as o-nitro-benzoic, since the decrease in the concentration of the base, caused by its conversion into salts, outweighs the catalytic effect of the acid. This, indeed, is seen in Fig. 5. 

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