The death of professor Rolf Huisgen (1920-2020) was announced on March 26th 2020, in the midst of the COVID-19 pandemic. Professor Huisgen was professor emeritus at the University of Munich in Germany, and studied in detail the mechanism of the 1,3-dipolar cycloaddition reaction, significantly expanding its scope. Even though he did not discover this reaction, it was through his studies that it became important in organic synthesis. Indeed, in honor of his work, the reaction became known as Huisgen’s cycloaddition and it has been consolidated as a useful method for the preparation of five-membered heterocyclic compounds. Considering these facts, in this review we provide an overview on the applications of 1,3-dipolar cycloaddition reactions, starting with the seminal examples in the field and further discussing the most recent applications.

A novel method for the synthesis of nonsymmetrical 3,3’-(aryl/alkyl-methylene)bis-2-hydroxy-1,4-naphthoquinones was developed by using the Mannich adduct of naphthoquinone and the reaction with another moiety of 2-hydroxy-1,4-naphthoquinone. This novel method produces for the first time nonsymmetrical 3,3’-(aryl/alkyl-methylene)bis-2-hydroxy-1,4-naphthoquinones. In a preliminary study, these compounds (15c, 15f and 15h) were evaluated regarding their effect over the viability of PC3 metastatic prostate cancer cell using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays at 100 µM. Three of these compounds presented relevant cytotoxic effects at 72 h posttreatment.

Vários estudos têm mostrado o potencial citotóxico de derivados da nor-β-lapachona contra células tumorais. Considerando a nor-β-lapachona um importante protótipo, uma série inédita de nor-β-lapachonas substituídas em C-3 foi sintetizada através de uma nova metodologia sintética envolvendo intermediário sintético 3-hidróxi-nor-β-lapachona para o acoplamento de alguns nucleófilos contendo núcleos derivados de carboidratos ou 2H-pirazóis. Todos os derivados foram avaliados frente a quatro linhagens de células tumorais. Duas das substâncias apresentaram moderada citotoxicidade, enquanto as demais inibiram fortemente todas as linhagens tumorais testadas.

Several studies have demonstrated the cytotoxic potential of nor-β-lapachone derivative against cancer cells. Considering nor-β-lapachone as an important prototype, a set of new 3-substituted nor-β-lapachones was synthesized by a new synthetic route that involves the use of synthetic intermediate generated for coupling with several nucleophiles containing the carbohydrate and 2H-pyrazole substituent moieties. All the compounds were screened against four tumor cell lines. Two of the compounds showed moderate cytotoxicity, while the other compounds strongly inhibit all tested cancer cell lines.

Prof. Ernest Wenkert's connections with Brazil on this side of the Atlantic Ocean involved two important links: Profs. Jayr de Paiva Campello and Otto R. Gottlieb. The former, along with Prof. Giuseppe Cilento, was one of those responsible for setting up the Institute of Chemistry of UNICAMP, while Otto Gottlieb was the great pioneer of Natural Products Chemistry in Brazil. The bridge between these two professors and Wenkert paved the way for several Brazilian chemists to visit the USA, and was also important for bringing some PhDs to Brazil.

Cálculos teóricos utilizando os funcionais B3LYP e PBE1PBE e as bases 6-31G(d) e 6-311+G(2d,p) para o sistema 3-(2-fenil-hidrazona)-naftaleno-1,2,4-triona, em solução (dmso) e em fase gasosa, evidenciaram, em ambos os casos, a maior estabilidade da forma ceto-hidrazona (rotâmeros Ia e Ib) comparada às formas enol-azo (rotâmeros IIa/IIb, por volta de 14 kcal mol-1) e III (aproximadamente 6 kcal mol-1). A natureza do substituinte no grupo fenil não influenciou a estabilidade relativa dos tautômeros. Estes resultados foram confirmados por dados espectroscópicos dos derivados HL1-HL13, sintetizados a partir da 2-hidroxi-1,4-naftoquinona e arilaminas (R = 4-OMe, 4-N2-C6H5, 4-Cl, 4-I, 3-I, 2-I, 4-COOH, 3-COOH, 4-CN, 3-CN, 4-NO2, 3-NO2, 2-NO2). A avaliação da atividade anticâncer in vitro (contra linhagens de células cancerosas SF-295, HCT-8, MDAMB-435 e HL-60) e bactericida (Bacillus cereus, Bacillus subtilis, Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, Klebsiella pneumonia e Pseudomonas aeruginosa) dos compostos HL1-HL13 e dos seus respectivos complexos de cobre(II), [Cu(L1-13)2], foi avaliada. Em geral a atividade bactericida foi baixa, exceto para o derivado HL5 (R = 3-I), mais ativo do que o controle; entretanto, seu complexo não foi ativo. Por outro lado, a complexação levou, em geral, ao aumento da atividade antitumoral dos pré-ligantes. O complexo [Cu(L13)2] (R = 3-NO2) apresentou moderada citotoxicidade contra leucemia humana (HL-60).

DFT calculations using the B3LYP and PBE1PBE functionals with the standard 6-31G(d) and 6-311+G(2d,p) basis sets were carried out for the 3-(2-phenylhydrazone)-naphthalene-1,2,4-trione system in solution (dmso) and in the gas phase, and showed the keto-hydrazone forms (rotamers Ia and Ib) to be more stable than the enol-azo forms (rotamers IIa and IIb, by about 14 kcal mol-1) and III (by approximately 6 kcal mol-1), independently of the nature of the substituent in the phenylene ring. These results were confirmed by spectroscopic data on the derivatives HL1-HL13, obtained from 2-hydroxy-1,4-naphthoquinone and arylamines (R = 4-OMe, 4-N2-C6H5, 4-Cl, 4-I, 3-I, 2-I, 4-COOH, 3-COOH, 4-CN, 3-CN, 4-NO2, 3-NO2, 2-NO2). The in vitro antitumor (against SF-295, HCT-8, MDAMB-435 and HL-60 cancer cell lines) and antibacterial activities (Bacillus cereus, Bacillus subtilis, Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, Klebsiella pneumonia and Pseudomonas aeruginosa) of compounds HL1-HL13 and of their respective copper(II) complexes, [Cu(L1-13)2], were tested. In general, these compounds exhibited low antibacterial activity, except for HL5 (R = 3-I), more active than the control; however, the corresponding complex was inactive. In contrast, increased cytotoxicity was observed upon complexation. Complex [Cu(L13)2] (R = 3-NO2) presented moderate cytotoxicity against human leukemia (HL-60).

Foram sintetizados, em um único pote reacional, alguns derivados da α- e β-lapachonas a partir de reação de hetero Diels-Alder, em etanol aquoso, entre estirenos substituídos (como dienófilos) e o-quinonas metídeos (o-QMs) metilênicas e arílicas geradas por condensação de Knoevenagel da 2-hidróxi-1,4-naftoquinona com formaldeído e aldeídos aromáticos.

Methylene and aryl o-quinone methides (o-QMs) generated by Knoevenagel condensation of 2-hydroxy-1,4-naphthoquinone with formaldehyde and arylaldehydes, undergo facile hetero Diels-Alder reaction with some substituted styrenes (as dienophiles) in aqueous ethanol media providing derivatives of α- and β-lapachone.

The microwave oven became an important source of heating for many laboratory procedures including accelerating organic reactions. Reactions that require long reflux times can sometimes be carried out in a few hours or minutes in a conventional microwave oven. However, longer reflux times can be troublesome since domestic microwave ovens are not prepared for these harsh conditions. This technical note presents our finding on heterogeneous catalysis transesterification reactions between b-keto-esters and carbohydrate derivatives under heating or microwave irradiation using an adapted domestic microwave oven.