Reaction of glycosyl isothiocyanate (1a) with amino acids such as ethyl L-phenylalaninate hydrochloride, ethyl L-leucinate hydrochloride and ethyl β-alaninate hydrochloride afforded glycosyl thioureides (3a. b, c) in good yields. Reaction of D-gluconyl isothiocyanate (1c) with amino acids (glycine, β-alanine, γ-aminobutyric acid, ε-aminocaproic acid) or p-aminobenzoic acid gave the corresponding D-gluconamides (4a, b, c, d) and/or D-gluconyl thioureides (5a, b, 7, 8). Treatment of 1a, b, c with 6-aminopenicillanic acid (6-APA) or ampicillin in the presence of triethylamine gave triethylammonium 6-(substituted thioureido) penicillanates (9a, b, c) and triethylammonium 6-(D-glycosyl thioureido) benzylpenicillanates (10a, b). The reaction between 1c and phenacyl 6-APA afforded phenacyl 6-(D-gluconyl thioureido) penicillanate (9d).