Theoretical Investigation of Regiodivergent Addition of Anilines and Phenolates to p-Benzoquinone Ring.

Two different products were obtained by the regiodivergent reaction of benzoquinone derivatives with phenolates and anilines: 3-aryloxybenzoquinone and 2-phenylamino-3-bromobenzoquinone. Calculated density functional theory free energies of reaction values corroborate the experimental observation of the formation of the substitution product in the reaction with phenolates in acetonitrile and the product of addition/oxidation for the reaction with aniline in water. Calculated charges and Fukui functions are similar for C2 and C3 atoms, indicating an equal possibility to suffer a nucleophilic attack. The calculated energy barriers for nucleophilic attack steps indicated that the first steps of the substitution with phenolates and addition/oxidation with anilines are faster, which justifies the formation of the respective products. The natural bond order analysis for the transition states revealed that there is a strong interaction between lone pairs of N and O atoms and the πC2C3 * for the O → C2 and N → C3 attacks and a weak interaction for the O → C3 and N → C2 attacks, which also agrees with experimental observations.

Synthesis and antimicrobial evaluation of amino sugar-based naphthoquinones and isoquinoline-5,8-diones and their halogenated compounds.

Antibiotic resistance has emerged as a serious global public health problem and lately very few antibiotics have been discovered and introduced into clinical practice. Therefore, there is an urgent need for the development of antibacterial compounds with new mechanism of action, especially those capable of evading known resistance mechanisms. In this work two series of glycoconjugate and non-glycoconjugate amino compounds derived from of isoquinoline-5,8-dione and 1,4-naphthoquinone and their halogenated derivatives were synthesized and evaluated for antimicrobial activity against Gram-positive (Enterococcus faecalis ATCC 29212, Staphylococcus aureus ATCC 25923, S. epidermidis ATCC 12228, S. simulans ATCC 27851) and Gram-negative bacteria (E. coli ATCC 25922, Proteus mirabilis ATCC 15290, K. pneumoniae ATCC 4352 and P. aeruginosa ATCC 27853) strains of clinical importance. This study revealed that glycoconjugate compounds derived from halogeno-substituted naphthoquinones were more active against Gram-negative strains, which cause infections whose treatment is even more difficult, according to the literature. These molecules were also more active than isoquinoline-5,8-dione analogues with minimum inhibitory concentration (MIC = 4-32 µg/mL) within Clinical and Laboratory Standard Institute MIC values (CLSI 0.08-256 µg/mL). Interestingly the minimal bactericidal concentration (MBC) values of the most active compounds were equal to MIC classifying them as bactericidal agents against Gram-negative bacteria. Sixteen compounds among eighteen carbohydrate-based naphthoquinones tested showed no hemolytic effects on health human erythrocytes whereas more susceptibility to hemolytic cleavage was observed when using non-glycoconjugate amino compounds. In silico Absorption, Distribution, Metabolism, Excretion and Toxicity (ADMET) evaluation also pointed out that these compounds are potential for oral administration with low side effects. In general, this study indicated that these compounds should be exploited in the search for a leading substance in a project aimed at obtaining new antimicrobials more effective against Gram-negative bacteria.