title: ortho-Halogen naphthaleins as specific inhibitors of Lactobacillus casei thymidylate synthase. Conformational properties and biological activity.
abstract: Thymidylate synthase (TS) (EC 2.1.1.45), an enzyme involved in the DNA synthesis of both prokaryotic and eukaryotic cells, is a potential target for the development of anticancer and antinfective agents. Recently, we described a series of phthalein and naphthalein derivatives as TS inhibitors. These compounds have structures unrelated to the folate (Non-Analogue Antifolate Inhibitors, NAAIs) and were selective for the bacterial versus the human TS (hTS). In particular, halogen-substituted molecules were the most interesting. In the present paper the halogen derivatives of variously substituted 3,3-bis(4-hydroxyphenyl)-1H,3H-naphtho[2,3-c]furan-1-one (1-5) and 3,3-bis(4-hydroxyphenyl)-1H,3H-naphtho[1,8-c,d]pyran-1-one (6-14) were synthesized to investigate the biological effect of halogen substitution on the inhibition and selectivity for the TS enzymes. Conformational properties of the naphthalein series were explored in order to highlight possible differences between molecules that show species-specific biological profile with respect to non species-specific ones. With this aim, the conformational properties of the synthesized compounds were investigated by NMR, in various solvents and at different temperatures, and by computational analysis. The apparent inhibition constants (K(i)) for Lactobacillus casei TS (LcTS) were found to range from 0.7 to 7.0 microM, with the exception of the weakly active iodo-derivatives (4, 10, 13); all] the compounds were poorly active against hTS. The di-halogenated compounds 7, 8, 14 showed the highest specificity towards LcTS, their specificity index (SI) ranging between 40 and >558. The di-halogenated 1,8-naphthalein derivatives (7-10) exhibited different conformational properties with respect to the tetra-haloderivatives. Though a clear explanation for the observed specificity by means of conformational analysis is difficult to find, some interesting conformational effects are discussed in the context of selective recognition of the compounds investigated by the LcTS enzyme.
authors.affiliation: Dipartimento di Chimica, Universita' degli Studi di Modena e Reggio Emilia, Via Campi 183 41100, Modena, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Ghelli
authors.forename: Marcella
authors.initials: M
authors.lastname: Rinaldi
authors.forename: Daniela
authors.initials: D
authors.lastname: Barlocco
authors.forename: Arianna
authors.initials: A
authors.lastname: Gelain
authors.forename: Piergiorgio
authors.initials: P
authors.lastname: Pecorari
authors.forename: Donatella
authors.initials: D
authors.lastname: Tondi
authors.forename: Giulio
authors.initials: G
authors.lastname: Rastelli
authors.forename: Maria Paola
authors.initials: MP
authors.lastname: Costi
mesh_terms: D018360:Crystallography, X-Ray; D004791:Enzyme Inhibitors / Q000138:chemical synthesis* / Q000494:pharmacology*; D006846:Hydrocarbons, Halogenated / Q000138:chemical synthesis* / Q000494:pharmacology*; D007780:Lacticaseibacillus casei / Q000201:enzymology*; D009682:Magnetic Resonance Spectroscopy; D009281:Naphthalenes / Q000138:chemical synthesis* / Q000494:pharmacology*; D011487:Protein Conformation; D011789:Quantum Theory; D021241:Spectrometry, Mass, Electrospray Ionization; D013940:Thymidylate Synthase / Q000037:antagonists & inhibitors*
chemical_list: D004791:Enzyme Inhibitors; D006846:Hydrocarbons, Halogenated; D009281:Naphthalenes; D013940:Thymidylate Synthase