COVID‐19 vaccines prevent severe forms of the disease, but do not warrant complete protection against breakthrough infections. This could be due to suboptimal mucosal immunity at the site of virus entry, given that all currently approved vaccines are administered via the intramuscular route. In this study, we assessed humoral and cellular immune responses in BALB/c mice after intranasal and intramuscular immunization with adenoviral vector ChAdOx1‐S expressing full‐length Spike protein of SARS‐CoV‐2. We showed that both routes of vaccination induced a potent IgG antibody response, as well as robust neutralizing capacity, but intranasal vaccination elicited a superior IgA antibody titer in the sera and in the respiratory mucosa. Bronchoalveolar lavage from intranasally immunized mice efficiently neutralized SARS‐CoV‐2, which has not been the case in intramuscularly immunized group. Moreover, substantially higher percentages of epitope‐specific CD8 T cells exhibiting a tissue resident phenotype were found in the lungs of intranasally immunized animals. Finally, both intranasal and intramuscular vaccination with ChAdOx1‐S efficiently protected the mice after the challenge with recombinant herpesvirus expressing the Spike protein. Our results demonstrate that intranasal application of adenoviral vector ChAdOx1‐S induces superior mucosal immunity and therefore could be a promising strategy for putting the COVID‐19 pandemic under control.

The spontaneous S-alkylation of the thyreostatic drug methimazole (1-methyl-1,3-dihydro-1H-imidazole-2-thione, 1) with 1,2-dichloroethane at room temperature, in dark or light conditions, led to the formation of its related substance 1,2-bis[(1-methyl-1H-imidazole-2-yl)thio]ethane, C10H14N4S2 (2a), primarily isolated in the form of dihydrochloride tetrahydrate [C10H16N4S2]Cl2·4(H2O) (2b), which crystallized in the monoclinic P21/c space group. Neutralization of 2b, followed by crystallization from the acetone/water mixture, produced dihydrate C10H14N4S2·2(H2O) (2c), which crystallized in the trigonal R-3 space group. Six water molecules in 2c are H-bonded mutually and to the nitrogen atoms of six molecules of 2a. DSC and TGA showed that 2c melts at 65 °C and loses water up to 120 °C. By cooling to room temperature, anhydrous 2a was obtained. Single crystals of 2a that are suitable for X-ray structure analysis were obtained by neutralization of 2b, followed by crystallization from dry dichloromethane. Anhydrous 2a crystallizes in the monoclinic P21/c space group. The dehydration of 2c led to the formation of the anhydrous product 2a, which is identical to the one obtained by crystallization, as was found by complementary solid-state techniques. No intermediate monohydrate or hemihydrate phases were detected. Powder diffraction showed the same pattern of 2c via both preparation procedures. The structures of all the forms were elucidated by spectroscopy, microscopy and thermal methods and confirmed by single crystal X-ray analysis.

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Spontaneous S-alkylation of methimazole (1) with 1,2-dichloroethane (DCE) into 1,2-bis[(1-methyl-1H-imidazole-2-yl)thio]ethane (2), that we have described recently, opened the question about its formation pathway(s). Results of the synthetic, NMR spectroscopic, crystallographic and computational studies suggest that, under given conditions, 2 is obtained by direct attack of 1 on the chloroethyl derivative 2-[(chloroethyl)thio]-1-methyl-1H-imidazole (3), rather than through the isolated stable thiiranium ion isomer, i.e., 7-methyl-2H, 3H, 7H-imidazo[2,1-b]thiazol-4-ium chloride (4a, orthorhombic, space group Pnma), or in analogy with similar reactions, through postulated, but unproven intermediate thiiranium ion 5. Furthermore, in the reaction with 1, 4a prefers isomerization to the N-chloroethyl derivative, 1-chloroethyl-2,3-dihydro-3-methyl-1H-imidazole-2-thione (7), rather than alkylation to 2, while 7 further reacts with 1 to form 3-methyl-1-[(1-methyl-imidazole-2-yl)thioethyl]-1H-imidazole-2-thione (8, monoclinic, space group P 21/c). Additionally, during the isomerization of 3, the postulated intermediate thiiranium ion 5 was not detected by chromatographic and spectroscopic methods, nor by trapping with AgBF4. However, trapping resulted in the formation of the silver complex of compound 3, i.e., bis-{2-[(chloroethyl)thio]-1-methyl-1H-imidazole}-silver(I)tetrafluoroborate (6, monoclinic, space group P 21/c), which cyclized upon heating at 80 °C to 7-methyl-2H, 3H, 7H-imidazo[2,1-b]thiazol-4-ium tetrafluoroborate (4b, monoclinic, space group P 21/c). Finally, we observed thermal isomerization of both 2 and 2,3-dihydro-3-methyl-1-[(1-methyl-1H-imidazole-2-yl)thioethyl]-1H-imidazole-2-thione (8), into 1,2-bis(2,3-dihydro-3-methyl-1H-imidazole-2-thione-1-yl)ethane (9), which confirmed their structures.