Synthesis and Photophysical Characterization of Fluorescent Naphtho[2,3-<i>d</i>]thiazole-4,9-Diones and Their Antimicrobial Activity against <i>Staphylococcus</i> Strains

The chemical reaction of 2-(methylsulfinyl)naphtho[2,3-d]thiazole-4,9-dione (3) using different amines, including benzylamine (4a), morpholine (4b), thiomorpholine (4c), piperidine (4d), and 4-methylpiperazine (4e), produced corresponding new tricyclic naphtho[2,3-d]thiazole–4,9–dione compounds (5a–e) in moderate-to-good yields. The photophysical properties and antimicrobial activities of these compounds (5a–e) were then characterized. Owing to the extended π-conjugated system of naphtho[2,3-d]thiazole–4,9–dione skeleton and substituent effect, 5a–e showed fluorescence both in solution and in the solid state. The introduction of nitrogen-containing heterocycles at position 2 of the thiazole ring on naphtho[2,3-d]thiazole-4,9-dione led to large bathochromic shifts in solution, and 5b–e exhibited orange-red fluorescence with emission maxima of over 600 nm in highly polar solvents. Staphylococcus aureus (S. aureus) is a highly pathogenic bacterium, and infection with its antimicrobial-resistant pathogen methicillin-resistant S. aureus (MRSA) results in serious clinical problems. In this study, we also investigated the antimicrobial activities of 5a–e against S. aureus, MRSA, and S. epidermidis. Compounds 5c with thiomorpholine group and 5e with 4-methylpiperazine group showed potent antimicrobial activity against these bacteria. These results will lead to the development of new fluorescent dyes with antimicrobial activity in the future

Similarity of odor qualities and similarity of molecules : Examples of molecules that contain a cis-type carbon-carbon double bond or a thioether moiety

The similarity of odor qualities by substituting the cis-type carbon-carbon double bond (cis -C=C-) for a thioether moiety (-S-) has been reported in some published papers. However, the degrees of the odor similarities were not reported. One of the objectives of this study is to measure the odor similarities by substituting the cis -C=C- for-S-. Another purpose of this study is to investigate the molecular features that contribute to the odor similarity in such cases. We employed the following two methods : 1) olfactory evaluations to measure the actual odor perception of the participants, and 2) computer chemistry to calculate the molecular features of the odorous compounds. As a result, it was confirmed that the odor quality did not significantly change in some cases though it was not a general trend when the cis -C=C- moiety was substituted for -S-. Similarities in the odors were mainly explained by the similarities in both the structural and electrostatic features based on the computational calculations. When the structural and electronic features were similar in two compounds, they are expected to produce si milar odors