6-Amino indazole

Amination at an azole ring nitrogen is known for Af-unsubstituted azoles. Thus 4,5-diphenyl-1,2,3-triazole with hydroxylamine-O-sulfonic acid gives approximately equal amounts of the 1- (104) and 2-amino derivatives (105) (74AHC(16)33). Pyrazole affords (106) and indazole gives comparable amounts of the 1- and 2-amino derivatives. 

Diazo coupling is expected to occur only with highly reactive systems, and experiment bears this out. Diazonium ions couple with the anions of N-unsubstituted imidazoles at the 2-position (e.g. 125 yields 126) and with indazoles (127) in the 3-position. In general, other azoles react only when they contain an amino, hydroxyl, or potential hydroxyl group, e.g. the 4-hydroxypyrazole (128), the triazolinone (129) and the thiazolidinedione (130) (all these reactions occur on the corresponding anions). 

N-Amination of indazole affords a mixture of 60% (271) and 40% (272), which compares with the 55 45 ratio obtained in methylation (Section 4.04.2.1.3(viii)). A camphopyrazole derivative (a mixture of tautomers 275 and 276) when treated with hydroxylamine O-sulfonic acid yields exclusively the (4S,7i )-4,7-methano-2-amino-7,8,8-trimethyl-4,5,6,7-tetrahydro-2H-indazole (277) (79YZ699). 

Substituents in the indazole ring may direct a given reaction towards another position either by their R and I electronic properties or simply by protecting the most reactive position. Examples of both types are found in sulfonation studies (67HC(22)l). As indicated before (Section 4.04.2.3.2(i)), sulfonation takes place at position 7. However, the presence of an amino group at positions 5 or 7 directs the attack towards the 4-position (Scheme 40). To obtain the indazole-5-sulfonic acid a more complicated procedure has been used but it is still based on the same ideas. 

The 3- or 5-aminopyrazoles are the synthons used most frequently. The second heterocyclic ring is created between the amino group and the 1-position (if unsubstituted) or between the amino group and the 4-position. Thus 3-substituted 5-aminopyrazoles react with 1,3-difunctional compounds to afford pyrazolo[l,5-a]pyrimidine derivatives (538) (Table 34). Aminopyrazolinones (R = OH) can be used instead of aminopyrazoles. Similarly 3-aminoin-dazole yields pyrimido[l,2-h]indazoles (539). 

This reactivity of A-unsubstituted amino-pyrazoles and -indazoles which can be regarded as 1,3-diamino derivatives has been used to build a great variety of fused six-membered heterocycles such as the 1,2,4-triazine derivatives (540) and (541), the 1,3,5-triazine derivatives (542) and (543), and benzothiadiazines (544). 

Finally, some results obtained from indazoles substituted in the carbocycle are of interest, even though in these cases the reaction does not involve the heterocyclic moiety (Section 4.04.2.3.2(ii)). For example, pyrazolo[3,4-/]- (566) and pyrazolo[4,3-/]-quinolines (567) have been obtained from aminoindazoles by the Skraup synthesis (76JHC899). Diethylethoxy-methylenemalonate can also be used to give (566 R = C02Et, R = OH) (77JHC1175). Pyrazolo-[4,3-/]- and -[4,3-g]-quinazolones (568) and (569) have been obtained from the reaction of formamide with 5-amino-4-methoxycarbonyl- and 6-amino-5-carboxyindazole, respectively (81CB1624). 

Most of the pharmacologically active indazole derivatives are useful as antiinflammatory drugs, e.g. bendazac or [(1-benzyl-l J/-indazol-3-yl)oxy]acetic acid (LDso in mice and rats of 355 and 388mgkg i.p., respectively) and benzydamine or l-benzyl-3-[3-(dimethyl-amino)propoxy]-l//-indazole (LDso in mice and rats of 110 and lOOmgkg" i.p., respectively). The last cited compound also has analgesic and antipyretic properties (B-76MI40404). 

In the search for new structures with antiinflammatory activities some 1-substituted 3-dimethylaminoalkoxy-lJ/-indazoles (704) have been synthesized and pharmacologically tested (66JMC38). Doses of 20-40 mg g i.p. produced sedation, muscle relaxation and motor incoordination, whereas doses of 80-100 mg kg produced depression. Toxicity was fairly constant in all series, varying from 120 to 150 mg kg i.p., with the exception of compounds possessing a nitro group or an amino group in the indazole nucleus, which provoked cyanosis. 

Analog erhalt man 5-Benzyloxy-3-(2-amino-athyl)-indol als Oxalat3 (81 % d.Th. F 162°, Zers.) bzw. 5-Benzyloxy-3-(2-amino-athyl)-indazol-Bis-hydrochlorid4 (30% d. Th. F 265°). 

A useful method for obtaining indazoles in high yields involves treatment of ortho-azido phenyl ketones or aldehydes with hydrazine hydrate. When this reaction was applied to 3-azido-2-formylselenophene, selenolo[3,2-c] pyrazole (111) was obtained in low yield. The yield could not be improved when the amino derivative was prepared as an intermediate142 (Scheme 13). 2-Dialkylamino-5-formylselenophenes react with diazonium salts under deformylation conditions to give azo dyes (Eq. 39).143 Another nitrogen-containing derivative of selenophene is compound U2.144 ... 

The photocyclization of cis-diaminomaleonitrile (372) to 4-amino-5-cyanoimidazole (373) has been shown to proceed via the trans isomer 374.308 4-Amino-3-cyanopyrazole does not seem to be an intermediate in this transformation.309 Analogous cyclizations have been reported in the imidazole 373 which undergoes further photoreaction to yield the bicycle 375, and in o-aminobenzonitrile which is converted into indazole.310 This photocyclization has been extended to include enaminonitriles 376 spectroscopic evidence for the intermediacy of iminoketenimes 377 in this311 and other similar transformations312 have been reported. 

Dinitro>6>aminoacid with ammonia... 

A ring closure may occur by reaction between a nitroso group and an amino group thus o-nitrobenzylamines (98) may be reduced to the hydrox-ylamine in an ammonia buffer and the hydroxylamino group oxidized to a nitroso group. If the amino group is primary or secondary, indazoles (99) are formed159 [Eq. (77)]. 

The effect of amino, hydroxy or mercapto substituents is to increase hydrogen bonding properties. However, if stable hydrogen bonds are formed in the crystal, then this can decrease their solubility in water (63PMH(l)177), e.g. indazole and benzimidazole are less soluble than benzoxazole. 

Amino- (459) and 3-amino-quinazolin-2-ones (460) (75JCS(Pl)3l), as well as 1-amino- and 2-amino-indazoles (92AHC(53)85) can be oxidized to 1,2,3-benzotriazines. C-Amino compounds can also give triazines oxidation of 3-aminoindazole (461) with hydrogen peroxide forms 1,2,3-benzo-triazin-4-one (462) <1899LA(305)289). 

The first information (37JGU739 67CB2164) about the synthesis of 1,2-dihydrobenzo[crf]indazole by reduction of 1,8-dinitronaphthalene or naphtho[equilibrium with 1,3- and l,5-dihydrobenzo[c[Pg.43]

The synthesis of pazopanib (1) involves sequential animation of 2,4-dichloropyrimidine 25 with 6-amino-2,3-dimethylindazole 24 and 5-amino-2-methyl-benzenesulfonamide 28. The 6-amino-2,3-dimethylindazole 24, on the other hand, was prepared from 2-ethylphenylamine 20 via 5-nitration with fuming nitric acid and concentrated sulfuric acid, followed by treatment with isoamyl nitrite and acetic acid to produce 6-nitro-3-methylindazole 22. The 6-nitro group was reduced with stannous chloride and concentrated HC1 in glyme and subsequently methylated at the C2 position of the indazole ring with trimethyloxonium tetrafluoroborate in acetone to produce 6-amino-2,3-dimethylindazole 24. The resultant indazole 24 was condensed with 2,4-dichloropyrimidine 25 in the presence of sodium bicarbonate in ethanol/THF and subsequent iV-methylation with iodomethane and cesium carbonate to produce 27. The 2-chloro group of pyrimidine was then allowed to react with 5-amino-2-methyl-benzenesulfonamide 28 in catalytic HCl/isopropanol and heated to reflux to deliver pazopanib hydrochloride (1) in good yield. 

Groessl M, Reisner E, Hartinger CG, Eichinger R, Semenova O, Timerbaev AR, Jakupec MA, Arion VB, Keppler BK (2007) Structure-activity relationships for NAMI-A-type complexes (HL)[trans-RuC14L(S-dmso)ruthenate(in)] (L = imidazole, indazole, 1, 2, 4-triazole, 4-amino-1, 2, 4-triazole, and 1-methyl-l, 2, 4-triazole) aquation, redox properties, protein binding, and antiproliferative activity. J Med Chem 50 2185-2193... 

Thermal cyclization was also the route employed to prepare 9-hydroxy-7-methyl-l/f-pyrazolo[3,4-/]quinoline (74) from the 6-aminoindazole/ethyl acetoacetate condensation adduct shown in Equation (41) <92JMC4595>. The hydroxyl substituent of compound (74) was then converted (POCl3, DMF) to a chloro, which in turn was displaced by treatment with aryl amines to give tricyclics with potent in vivo immunostimulatory activity like that noted for regioisomeric l//-imidazo[4,5-/]quinolines but unlike the inactive pyrazolo[4,3-/]quinolines. Although it was noted with some interest that none of the linear tricyclic isomer had been isolated, this finding actually parallels that reported earlier for the similar condensation of 1- and (V(6)-alkyl and unsubstituted 6-amino-indazoles with diethyl ethoxymethylenemalonate <83JHC1351>. 

A number of heterocyclic aniline derivatives afforded moderate to good yields of the diarylamines. Among the reported systems were amino-indazole,106,106a aminobenzodioxole,107 and aminobenzodioxanne.98,108 In the latter series, good to excellent yields were obtained with the primary aniline, but modest yields were observed after monoalkylation of the amino group (Equation (81)). 

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