{"id":996,"date":"2023-11-22T04:09:05","date_gmt":"2023-11-22T09:09:05","guid":{"rendered":"https:\/\/www.creative-peptides.com\/blog\/?p=996"},"modified":"2023-11-22T04:25:49","modified_gmt":"2023-11-22T09:25:49","slug":"do-peptide-drugs-need-acylation-blocking-at-n%ce%b1","status":"publish","type":"post","link":"https:\/\/www.creative-peptides.com\/blog\/do-peptide-drugs-need-acylation-blocking-at-n\/","title":{"rendered":"Do Peptide Drugs Need Acylation Blocking at N\u03b1?"},"content":{"rendered":"\n

<\/a>The formation of 2,5-diketopiperazine<\/a> (DKP) with a bicyclic structure is one of the most detrimental side reactions and degradation pathways affecting peptide synthesis<\/a>. Despite its crucial role as a versatile building block in drug discovery, the formation of DKP reactions is highly undesirable in the production of peptide drugs. DKP formation can occur during the process of peptide drug formulation<\/a>, as well as in the storage of starting materials and finished products, and may even occur under solid-phase synthesis<\/a> conditions.<\/p>\n\n\n\n

Mechanism of DKP Formation<\/strong><\/h2>\n\n\n\n

DKP can be formed through acid- or base-catalyzed reactions. The nucleophilic attack by the N\u03b1 group of the peptide on the carbonyl group between the second and third amino acid residues, either as an amide or ester carbonyl, leads to the cleavage of the amide or ester bond. The N-terminal dipeptide, as a derivative of the six-membered ring DKP, is separated from the peptide molecule. Consequently, the peptide molecule is truncated at its N-terminus by two amino acid residues, forming a byproduct characteristic of DKP. When the involved peptide is a depsipeptide (X=O in Figure 1), the formation of DKP is accelerated, as hydroxy derivatives act as better leaving groups than their amino counterparts.<\/p>\n\n\n

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\"Mechanism<\/a>
Figure 1. Mechanism of DKP formation.<\/figcaption><\/figure><\/div>\n\n\n

FDA-<\/strong>a<\/strong>pproved Peptide Drugs<\/strong><\/strong><\/h2>\n\n\n\n

Considering the common occurrence of degradation in peptides with N\u03b1 groups, whether the N-terminus should be blocked to prevent DKP formation becomes a crucial consideration in peptide drug design<\/a>. In fact, there are peptide drugs on the market that have a free N\u03b1 group. It is noteworthy that several peptide entities at their N-terminus are blocked through acylation, cyclization, or pyroglutamation. In peptide drugs where N\u03b1 is not blocked, they are often cyclic peptides with disulfide bonds or amide cyclization, or they may be prodrugs. Cyclization is known to effectively limit N\u03b1 activity, thereby reducing the formation of DKP. There are also three peptide drugs with free N\u03b1, namely Golotimod<\/a>, Thymodepressin, and NOV-002, which are actually derivatives modified from (L\/D)-Glu side chain carboxylate salts. In these cases, the formation of DKP is also hindered.<\/p>\n\n\n\n

Peptide Name<\/td>Tradename<\/td>Amino Acid Count<\/td>N-terminal Dipeptide Structure<\/td><\/tr>
Macimorelin<\/td>Macrilen<\/td>3<\/td>Aib-Trp<\/td><\/tr>
Thymopentin<\/a><\/td>Timunox<\/td>5<\/td>Arg-Lys<\/td><\/tr>
Semax<\/a><\/td>Semax<\/td>7<\/td>Met-Glu<\/td><\/tr>
Saralasin<\/a><\/td>Sarenin<\/td>8<\/td>Sar-Arg<\/td><\/tr>
Angiotensin II<\/a><\/td>Giapreza<\/td>8<\/td>Asp-Arg<\/td><\/tr>
Icatibant<\/a><\/td>Firazyr<\/td>10<\/td>D-Arg-Arg<\/td><\/tr>
Alloferon<\/td>Allokine-alpha<\/td>13<\/td>His-Gly<\/td><\/tr>
P-15<\/td>PepGen P-15<\/td>15<\/td>Gly-Thr<\/td><\/tr>
Difelikefalin<\/a><\/td>Korsuva<\/td>5<\/td>Phe-Phe<\/td><\/tr><\/tbody><\/table>
Table 1. Examples of short peptides with a free N\u03b1 group approved by the FDA.<\/figcaption><\/figure>\n\n\n\n

Characteristics of Peptides Prone to DKP Formation<\/strong><\/h2>\n\n\n\n