Passage
The β-lactam scaffold is an important feature in a class of broad-spectrum antibiotics that includes the penicillins, cephalosporins, and monobactams. These antibiotics are used to treat a variety of diseases caused by bacteria. The penicillins work by inhibiting a step in the synthesis of peptidoglycan. However, the development of antibiotic resistance in the form of enzymes such as β-lactamase is an ongoing problem.An aromatic ring linked to the β-lactam ring has been reported to participate in hydrophobic interactions with β-lactamase active sites, and an aromatic ring bonded to the nitrogen of the β-lactam has shown to be beneficial to biological activity. With this in mind, researchers synthesized a group of penicillanic acid analogues with substituted aromatic rings bonded to the β-lactam ring in an effort to overcome the challenge of antibiotic resistance. The substituents on the aromatic rings were varied, including -OCH₃ and -NO₂, to make several analogues. A key step in the synthesis of these analogues was the coupling of Compounds 1 and 2 to form a compound with two β-lactam rings (Reaction 1) .
Reaction 1The researchers studied the analogues' structure-activity relationship and antimicrobial activity against the gram-negative bacteria Escherichia coli and the gram-positive bacteria Staphylococcus aureus. Ampicillin, a penicillin derivative used to treat illnesses brought about by gram-positive and gram-negative bacteria, was used as a control. The minimal inhibitory concentrations are shown in Table 1.Table 1 Minimal Inhibitory Concentration (MIC)
The penicillanic acid analogues were tested for their effect on mammalian cell viability because toxicity to cells is also an important factor to consider for potential drug candidates. The general acceptable level of cell viability for a drug candidate is 70%. These results are shown in Figure 1.
Figure 1 Cell viability assay results
Adapted from De rosa M, Vigliotta G, Palma G, Saturnino C, Soriente A. Novel Penicillin-Type Analogues Bearing a Variable Substituted 2-Azetidinone Ring at Position 6: Synthesis and Biological Evaluation. Molecules. 2015.
-The synthesis of Compound 1 requires hydrolysis of an ester with LiOH and produces a carboxylate ion. The reaction is quenched in the next step by the addition of HCl. What is the expected result if blue litmus paper is immersed in the fully quenched solution? The blue litmus paper will:

Question

Passage
The β-lactam scaffold is an important feature in a class of broad-spectrum antibiotics that includes the penicillins, cephalosporins, and monobactams. These antibiotics are used to treat a variety of diseases caused by bacteria. The penicillins work by inhibiting a step in the synthesis of peptidoglycan. However, the development of antibiotic resistance in the form of enzymes such as β-lactamase is an ongoing problem.An aromatic ring linked to the β-lactam ring has been reported to participate in hydrophobic interactions with β-lactamase active sites, and an aromatic ring bonded to the nitrogen of the β-lactam has shown to be beneficial to biological activity. With this in mind, researchers synthesized a group of penicillanic acid analogues with substituted aromatic rings bonded to the β-lactam ring in an effort to overcome the challenge of antibiotic resistance. The substituents on the aromatic rings were varied, including -OCH₃ and -NO₂, to make several analogues. A key step in the synthesis of these analogues was the coupling of Compounds 1 and 2 to form a compound with two β-lactam rings (Reaction 1) .

Reaction 1The researchers studied the analogues' structure-activity relationship and antimicrobial activity against the gram-negative bacteria Escherichia coli and the gram-positive bacteria Staphylococcus aureus. Ampicillin, a penicillin derivative used to treat illnesses brought about by gram-positive and gram-negative bacteria, was used as a control. The minimal inhibitory concentrations are shown in Table 1.Table 1 Minimal Inhibitory Concentration (MIC)

The penicillanic acid analogues were tested for their effect on mammalian cell viability because toxicity to cells is also an important factor to consider for potential drug candidates. The general acceptable level of cell viability for a drug candidate is 70%. These results are shown in Figure 1.

Figure 1 Cell viability assay results
Adapted from De rosa M, Vigliotta G, Palma G, Saturnino C, Soriente A. Novel Penicillin-Type Analogues Bearing a Variable Substituted 2-Azetidinone Ring at Position 6: Synthesis and Biological Evaluation. Molecules. 2015.
-The synthesis of Compound 1 requires hydrolysis of an ester with LiOH and produces a carboxylate ion. The reaction is quenched in the next step by the addition of HCl. What is the expected result if blue litmus paper is immersed in the fully quenched solution? The blue litmus paper will:

Quizplus · Accepted Answer

11ecba2d_1272_2e0a_a3bf_49c7e2697ffe_MD0008_00 Litmus paper is coated with litmus dye that changes color depending on the pH of the solution in which it is immersed and used as a pH indicator to determine whether a solution is acidic or basic. An acidic (pH <7) solution will change blue litmus paper to red whereas a basic (pH >7) solution will turn red litmus paper blue. Hydrolysis of an ester with the base LiOH creates a carboxylate ion and will have a pH >7 because LiOH is a strong base. Protonation of the carboxylate ion requires the addition of an acid such as HCl. The addition of acid to the basic solution causes the pH of the reaction mixture to decrease, becoming more acidic. Carboxylic acids are weak acids with pK_a values near 4, so the pH of a solution of carboxylate ions must be brought below 4 to fully protonate the ions. The pH of the mixture can be monitored using litmus paper. When enough acid is added to the reaction and carboxylate ions become protonated, the blue litmus paper will turn red. (Choice B) The blue litmus paper will turn red; however, the carboxylate was already deprotonated before quenching, and addition of an acid to the reaction will protonate the carboxylate. (Choice C) The solution is acidic because the addition of the strong acid HCl decreases the pH of the reaction; however, an acidic solution will turn blue litmus paper red. (Choice D) Blue litmus paper remains blue in basic solutions. The initial reaction mixture is basic because LiOH is used for the ester hydrolysis, but it becomes acidic with the addition of an acid. Educational objective: Litmus paper is used as a pH indicator. In acidic solutions (pH <7), blue litmus paper will turn red; in basic solutions (pH >7), red litmus paper will turn blue. The addition of an acid to a solution will protonate bases such as carboxylate ions.

Passage The β-Lactam Scaffold Is an Important Feature in a Class