Heterocyclic groups

The nitration of phenylpyridines and related compounds has attracted attention for a long time, and measurements of isomer proportions have been made for several compounds of this type. Nitration occurs in the phenyl ring. For 2-phenylpyridine and 2-phenylpyridine i-oxide measurements of the dependence of rate of nitration upon acidity in 75-81 % sulphuric acid at 25 °C show that both compounds are nitrated as their cations (table 8.1). The isomer distribution did not depend significantly upon the acidity, and by comparison with the kinetic data for quinolinium ( 10.4.2) the partial rate factors illustrated below were obtained.They should be compared with those for the nitration of 2-nitrobiphenyl ( 10.1). The protonated heterocyclic groups are much... 

Table III-124 Thiazoles substituted by several heterocyclic groups. ...

Table III-125 Thiazoles substituted by heterocyclic groups nonadjacent to the...

TABLE III-125. THIAZOLES SUBSTITUTED BY HETEROCYCLIC GROUPS NONADJACENT TO THE THIAZOLE RING... 

Fig. 4. R groups having reactive heterocyclic groups attached to (8) through NH.

From thiohydrazides, R CS NHNHg, in which R is an aromatic or a heterocyclic group, 1,2,3,4-thiatriazoles may in general be obtained in good yield by treatment with nitrous acid. ... 

The alkylation of formazan anions (166) with methyl iodide yields the A-methylformazan (202) which cannot be prepared by direct methods (Scheme 31).4 However, formazans that contain hydroxyaryl (203) or heterocyclic groups (205) alkylate preferentially on these groups to yield the alkylation products 204349 and 206,346-348 respectively (Eqs. 24,25). Although formazans are resistant to acylation,334,350 351 it can be accom-... 

Various organometallic complexes containing heterocyclic group 15 rings are known. These are often formed in complex reactions. For example, a mixture of the phosphacyclopentadienes 111 and 112 reacts slowly with distilled calcium metal to yield the tetranuclear 113 (Figure 58).301 The centra symmetric Ca2Cl2 core is nearly square, with... 

Syntheses, structures and properties of heterocyclic group 13/15 compounds of the type [R2M LR 2]V have been the subject of intense studies for many years. In particular, aminoalanes and -gallanes [IGIVINR/ (M = Al, Ga) have received considerable attention. The interest in these particular compounds has increased within the last two decades due to their potential application as single source precursors for the deposition of AIN and GaN... 

As the solid state structures of heterocyclic group 13 amides, phosphides and arsenides have been reviewed in the past,76 they will not be discussed here. Instead, the solid state structures of group 13 stibides and bismuthides will be described in detail. 

This class of compounds comprises a series of synthetic agents patterned after nalidixic acid, a naphthyridine derivative introduced in 1963 for the treatment of urinary tract infections. Isosteric heterocyclic groupings in this category include the quinolones (e.g., norfloxacin, ciprofloxacin, lome-floxacin, gatifloxacin, sparfloxacin, moxifloxacin, and ofloxacin), the naph-thyridones (e.g., nalidixic acid, enoxacin, and trovafloxacin), and the cin-nolones (e.g., cinnoxacin) [2] (Fig. 1). 

Table 16.5 General structure of a sulfa drug, structure of five sulfa drugs containing six-mem-bered heterocyclic R substituents, and measured pK values pK values were calculated using a spectrophotometric titration. Errors represent the 95% confidence levels and both the values and the associated errors were obtained from fits of the data using Scientist for Windows. Reprinted with permission from Boreen AL, Arnold WA, McNeil K (2005) Triplet-sensitized photodegradation of sulfa drugs containing six-membered heterocyclic groups identification of an S02 extrusion photoproduct. Environ Sci Technol 39 3630-3638. Copyright 2005 American Chemical Society...

There are two possibilities for practical implementation. If the polymers with the heterocyclic groups are to be isolated in powder form, the polycyclocondensation can be achieved in the same reaction mixture, i.e., in solution. However, if the polymer is to be isolated in the form of fibers, foils, coatings, or adhesives, the following procedure is appropriate The soluble, still reactive polymers of the first reaction step are poured out, e.g., as a film, or spun into a fiber. Then the solvent is evaporated and afterwards the polycyclocondensation is carried out by heating the finished article in the solid state. 

A large number of derivatives of the penicillin (e.g., 449) and cephalosporin (e.g., 450) types have been prepared with A -acyl residues containing meso-ionic heterocyclic groupings. Some have shown antistreptococcal and antistaphylococcal activities in vivo. 

The synthesis of heterocyclic group 13/15 compounds of the type [R2MER 2]jc has been investigated for many years [21]. General synthetic pathways such as dihydrogen, alkane and salt elimination reactions as summarized in Scheme 3... 

This short review has described the synthesis of Lewis acid-base adducts and heterocyclic group 13/Sb compounds. In particular the synthesis of the hete-ro cycles required the development of new synthetic strategies. The distibine... 

Compounds which enhance the catalytic activities of the CAs are known as activators. Activators of carbonic anhydrases are less studied because CA is one of the most efficient enzymes known. Carbonic anhydrase II activation by phosphorylation in the presence of protein kinase and cAMP has been reported (195,196). Also some anions are activators for CA III (197,198) the catalytic effect is due to the proton shuttling capacities of such activators. Histamine, a well known activator, for native and Co(II)-substituted isoenzymes I and II CA is reported by Briganti et al. (199). Amines [Ar-CH(R3)CH(R2)NH(R1) Ar =Aromatic/heterocyclic group R1 =R2 = H, Me R3 = H, OH, COOH] and amino acids are efficient activators for CA I—III (200-207). These amines possess a bulky aromatic/heterocyclic moiety in their molecular structure and act as proton acceptor (204-207). 

Boreen, A.L., Arnold, X.A. and McNeill, K. (2004) Photochemical fate of sulfa drugs in the aquatic environment sulfa drugs containing five-membered heterocyclic groups. Environ. Sci. Technol., 38 (14), 3933-3940. 

G eometry-optimized CNDO/2 calculetions are carried out in an attempt to predict the effect of protonation on the conformational characteristics and geometry of PBO model compounds. Values of the conformational energy vs. rotation of the end-phenylenes about the heterocyclic group are calculated for c/s-PBO model compounds in the unprotonated form and as 2H + and 4H + ions. 

The medicinal use of arsenic compounds is now very limited, but some are still used in human trypanosomiasis. The effect of heterocyclic groups in reducing toxicity is well shown in the trypanocide melarsoprol (Mel B) (263), in which the severe toxicity of sodium arsanilate (atoxyl) has been reduced successively by substitution with a triazine residue and incorporation of the arsenic atom in a heterocycle. 

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