Abstract: A novel quinolinecarboxylic acid derivative of the formula ##STR1## or a pharmaceutically acceptable salt thereof. These compounds are useful as antibacterial agents, and are prepared by a process which comprises reacting a compound of the formula ##STR2## with a compound of the formula ##STR3##wherein X represents a halogen atom, and thereafter, as required, converting the resulting compound to a pharmaceutically acceptable salt thereof.

Abstract: A 1,1-dioxopenicillanic acid ester represented by formula (I) ##STR1## wherein R represents a methyl or phenyl group. The ester of formula (I) may be prepared by reacting 1,1-dioxopenicillanic acid or its salt with a compound represented by formula (III) ##STR2## wherein R is as defined above, and X represents a halogen atom, or by oxidizing a compound of formula (V) ##STR3## wherein R is as defined above. The ester of the formula (I) is useful as a .beta.-lactamase inhibitor and may be used in association with a .beta.-lactam antibiotic.

Abstract: A process for producing a brominated 1,3-dioxolen-2-one of the following general formula (I) ##STR1## wherein R.sub.1 represents a hydrogen atom, a methyl group, or an aryl group, and R.sub.2 represents a hydrogen atom, or R.sub.1 and R.sub.2 may be bonded together to form --(CH.sub.2).sub.n -- in which n represents an integer of 3 to 5, which comprises reacting a compound of the following formula (II) ##STR2## wherein R.sub.1 and R.sub.2 are as defined, with bromine under radical generating conditions.

Abstract: (5-Methyl-2-oxo-1,3-dioxolen-4-yl)methyl 6-[(hexahydro-1H-azepin-1-yl)methyleneamino]penicillanate of the following formula (I) ##STR1## or its pharmaceutically acceptable acid addition salt. The compound is useful as an antibacterial agent and may be prepared by reacting (5-methyl-2-oxo-1,3-dioxolen-4-yl)-methyl 6-aminopenicillanate of the following formula (II) ##STR2## or its acid addition salt with chloro-N,N-hexamethyleneformiminium chloride, and as required, converting the resulting compound to its pharmaceutically acceptable acid addition salt.

Abstract: A novel Ampicillin ester of the general formula ##STR1## wherein R.sub.1 represents a hydrogen atom, a methyl group or an aryl group, and R.sub.2 represents a hydrogen atom or may be taken together with R.sub.1 to form a divalent carbon chain residue, or its acid addition salt.The novel Ampicillin ester or its acid addition salt is prepared by (1) reacting a corresponding 6-N-acylamino penicillanic acid (II) or its salt with a compound of the formula ##STR2## wherein R.sub.1 and R.sub.2 are as defined above, and X is a halogen atom, or reacting a compound of the formula ##STR3## wherein R.sub.1 and R.sub.

Abstract: A 1,3-dioxolen-2-one derivative of the general formula ##STR1## wherein R.sub.1 represents a hydrogen atom, a methyl group, or an aryl group, R.sub.2 represents a hydrogen atom, or may be taken together with R.sub.1 to form a divalent carbon chain residue, and x represents a halogen atom.The above compounds can be prepared by reacting a compound of the general formula ##STR2## with a halogenating agent, and are useful as protective group-introducing reagents for introducing protective groups into reagents in various chemical reactions, or as modifiers for prodrug preparation in medicine.