Passage
Solid-phase peptide synthesis is normally carried out on a resin bathed multiple times in dimethylformamide (DMF) -a toxic, polar, aprotic solvent-which poses an environmental problem because a large amount of toxic solvent waste is created. Cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC) are nontoxic, polar, aprotic solvents that could be used as an alternative to DMF.Compounds 1 and 2 are modified L-amino acids. They were coupled to form Compound 3, a dipeptide, which was then deprotected to yield Compound 4 (Figure 1) .
Figure 1 Synthesis of Compound 4To determine the effect that solvent type and temperature have on the synthesis of this peptide, the nontoxic solvents PC and EC as well as the toxic solvent DMF were each used in separate syntheses of Compound 4 at different temperatures. The reaction solvent was also used to rinse the resin. Table 1 shows the results of these syntheses.Table 1 Results from the Synthesis of Compound 4
The successful synthesis of Compound 4 using nontoxic solvents encouraged researchers to pursue the synthesis of a larger, biologically active peptide. Bradykinin, a vasodilator containing nine amino acids (Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg) , was synthesized using the same solid-state peptide synthesis protocol used to synthesize Compound 4. Separate syntheses were done using either DMF or PC, and the purity of bradykinin from each synthesis was analyzed by high-performance liquid chromatography (HPLC) (Figure 2) .In each chromatogram, peak 1 has the same retention time as commercially obtained bradykinin, and the other peaks correspond to impurities. In chromatogram A, the impurity has a similar retention time to the product peak whereas the impurity peaks in chromatogram B have distinct retention times compared to the product peak.
Figure 2 HPLC of synthetic bradykinin: (A) synthesis in DMF; (B) synthesis in PC
Adapted from S. B. Lawrenson et al., "The greening of peptide synthesis." Green Chem. ©2017 The Royal Society of Chemistry.
-The most likely reason the resin was rinsed with the same solvent used for the reaction was to:

Question

Passage
Solid-phase peptide synthesis is normally carried out on a resin bathed multiple times in dimethylformamide (DMF) -a toxic, polar, aprotic solvent-which poses an environmental problem because a large amount of toxic solvent waste is created. Cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC) are nontoxic, polar, aprotic solvents that could be used as an alternative to DMF.Compounds 1 and 2 are modified L-amino acids. They were coupled to form Compound 3, a dipeptide, which was then deprotected to yield Compound 4 (Figure 1) .

Figure 1 Synthesis of Compound 4To determine the effect that solvent type and temperature have on the synthesis of this peptide, the nontoxic solvents PC and EC as well as the toxic solvent DMF were each used in separate syntheses of Compound 4 at different temperatures. The reaction solvent was also used to rinse the resin. Table 1 shows the results of these syntheses.Table 1 Results from the Synthesis of Compound 4

The successful synthesis of Compound 4 using nontoxic solvents encouraged researchers to pursue the synthesis of a larger, biologically active peptide. Bradykinin, a vasodilator containing nine amino acids (Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg) , was synthesized using the same solid-state peptide synthesis protocol used to synthesize Compound 4. Separate syntheses were done using either DMF or PC, and the purity of bradykinin from each synthesis was analyzed by high-performance liquid chromatography (HPLC) (Figure 2) .In each chromatogram, peak 1 has the same retention time as commercially obtained bradykinin, and the other peaks correspond to impurities. In chromatogram A, the impurity has a similar retention time to the product peak whereas the impurity peaks in chromatogram B have distinct retention times compared to the product peak.

Figure 2 HPLC of synthetic bradykinin: (A) synthesis in DMF; (B) synthesis in PC
Adapted from S. B. Lawrenson et al., "The greening of peptide synthesis." Green Chem. ©2017 The Royal Society of Chemistry.
-The most likely reason the resin was rinsed with the same solvent used for the reaction was to:

Quizplus · Accepted Answer

11ecba2d_129a_c44d_a3bf_e919d5fc107c_MD0008_00 A variable is a component of an experiment that is changed. To determine how the variable affects the experimental results, all other components of the experiment must be held constant. In the solid-phase peptide synthesis, the variable was the solvent used. Synthesis of bradykinin was carried out in two different solvents, DMF and PC, to determine which gave better results. If a different solvent was used in the rinse step than in the reaction step, the synthesis results could not be solely attributed to the solvent in which the reaction occurred. (Choice B) The type of solvent used to rinse the resin does not affect how much waste is created during peptide synthesis. The volume of solvent used to rinse the resin affects the amount of waste created. (Choice C) DMF and PC are both polar aprotic solvents, and are unlikely to produce different side reactions. (Choice D) The rate of peptide synthesis does not depend on the solvent used in the rinse step. The resin must be rinsed regardless of the type of solvent used. Educational objective: Variables are components of an experiment that change while other components of the experiment are held constant. These parameters must be isolated to determine the effect a variable has on the results of an experiment.

Passage Solid-Phase Peptide Synthesis Is Normally Carried Out on a Resin