Thiazole derivatives, activity

The same situation is observed in the series of alkyl-substituted derivatives. Electron-donating alkyl substituents induce an activating effect on the basicity and the nucleophilicity of the nitrogen lone pair that can be counterbalanced by a deactivating and decelerating effect resulting from the steric interaction of ortho substituents. This aspect of the reactivity of thiazole derivatives has been well investigated (198, 215, 446, 452-456) and is discussed in Chapter HI. 

The chemistry of thiazoles is interesting in view of their propensity for biological activity. Eor that reason thiazoloquinolines have also been a widely studied group of compounds. A preferred route to thiazoles exploits a-halogeno ketones in a reaction with thioamides to give the fused 2-substituted thiazole derivatives. 

A thiazole derivative that incorporates a fragment of the amphetamine molecule shows some CNS stimulant activity more specifically, the compound antagonizes the depression caused by overdoses of barbiturates and narcotics. Reaction of benzalde-hyde with sodium cyanide and benzenesulfonyl chloride gives the toluenesulfony1 ester of the cyanohydrin (141). Reaction of this with thiourea leads directly to aminophenazole (143) It is probable the reaction proceeds by displacement of the tosylate by the thiourea sulfur to give 142 addition of the amino group to the nitrile followed by tautomerization affords the observed product. ... 

Thiazolo[2,3-c][l,2,4]triazines 667 were synthesized by coupling the diazotized thiazole derivative 666 with activated nitriles to give 667 without... 

J ,3J ,4J ,5J )-2,5-bis(benzyloxy)-3,4-dihydroxy-Nd -bis (lS)-2-methyl-l-[(methylamino)carbonyl]propyl hexanediamide is a C2-symmetric HIV-1 protease inhibitor [29]. Derivatization in the para positions of the benzyl-oxy groups via microwave-assisted Stille reaction on the corresponding di-brominated inhibitor smoothly yielded the desired heteroarylated derivatives (Scheme 10). Interestingly, the 1,3-thiazole derivative showed a higher antiviral activity on the wild type virus than the lead compound. The activity remained at the same level in the presence of seriun. Unfortimately, a low activity was observed on mutants. 

The oxidation of a thiazolidine derivative to the corresponding thiazole using activated manganese dioxide in dichloromethane at 100 °C is shown in Scheme 6.100. Further manipulation of this molecule led to dimethyl sulfomycinamate, a methano-lysis product of the thiopeptide antibiotic sulfomycin I [203]. 

The synthesis of other biologically active thiazoles was described by Ohsumi et al. [50] and is shown in Scheme 16. Condensation of phosphonium bromide and 4-methoxy-3-nitrobenzaldehyde gave a 1 1 mixture of (Z)- and (-E)-stilbenes. ( )-stilbene 64 was purified by crystallization and then converted to bromohydrin 65 by NBS-H2O. Oxidation of the bromohydrin by DMSO-TFAA gave the bromoketone intermediate 66, which was condensed with thiocarbamoyl compounds in the presence of Na2C03 in DMF to give the corresponding 2-substituted thiazole derivatives (67a and b). Compound 67a... 

Levulinic acid is fairly easily converted into thiazole derivatives by the intermediate formation of an a-halogenated ketone such as the /3-bromo derivative (XL) or /3-chloro derivative, which reacts with thiourea to form 2-amino-4-methyl-5-thiazoleacetic acid (XLI) or with thioformamide to give 4-methyl-5-thiazoleacetic acid (XLII). The aminothiazole (XLI) and its ethyl ester (XLIII) have been converted into their corresponding sulfanilamide derivatives, (XLIV) and (XLV). These sulfanilamides, particularly the acid XLIV, have considerable chemotherapeutic activity moreover the acid possesses distinct solubility advantages over sulfathiazole itself. 

The chemistry of the thiazoles does, of course, bear some similarity to that of the oxazoles. Metallated thiazoles and thiazole derivatives have found use, for example, both as carbonyl equivalents and masked acetaldehyde enolates. Additionally, as will be exemplified below, thiazole derivatives have served as catalysts for benzoin-type condensations, and they have provided access to a unique class of activated acid derivatives. 

The latter approach has been exemplified in a number of published cases. An indication of the development requirements of well-known reactions for successful employment in array synthesis is provided by the work ofWatson and co-workers [15] to prepare thiazole derivatives. Adaptation of the Hantzch synthesis of 2-aminothiazoles (Fig. 2) from a-haloketones and thioureas was used in the one-step preparation of discrete samples. Inclusion in the array of a compound of known biological activity provided a valuable internal control. 

Figure 4. Metabolic behavior and activities of some O-type nitro-thiazole derivatives...

In this context, Hanumantharao et al. [ 129] have carried out a QSAR analysis of the agonist activity of the thiazole derivatives (e) with the molecular descriptors generated from the MOE programme [71]. This has resulted in QSAR models (Eq. 23 and 24) of these compounds in terms of hydropho-bicity of VdW surface areas with different polarities (SlogP, SlogPvsAo and SlogPvsAs). electrostatic potential energy (Eeie). and zero-order connectivity... 

Table13 Physicochemical/electronic properties and /Ss-agonist activity of thiazole derivatives (comp, e, Fig. 15) [129]... 

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