Cyclic amino acids (Accⁿ), where n represents the number of carbon atoms in the ring (Figure 1).

Cyclic amino acids are configuration-limited amino acids; Cyclic amino acids play an important role in the design and synthesis of bioactive peptides because of their structural rigidity, which can cause important conformational effects. Cyclic amino acids are often used in the sequence of polypeptides to find economic, efficient and bioactive peptides resistant to enzymatic degradation. They are also used in DNA or peptide nucleic acid (PNA) to stabilize their helix structure, which has a good application prospect in botany, biology, anti-inflammatory drugs, anti-tumor drugs, cancer cell detection and other aspects.

Application of Cyclic Amino Acids

1. Plant growth hormone regulator

Acc³ widely exists in the fruits of plants, is a new plant growth regulator, can be converted into ethylene under the action of enzymes, fruits, vegetables, tomatoes and other obvious ripening effect, has great economic significance in agriculture.

2. Anti-inflammatory activity

Acc⁶ can be used for the design and synthesis of anti-inflammatory drugs. For example: The tripeptide Formyl-Met-Acc⁶-Phe-OH can induce the release of pharmacotaxis and dissolution of neutrophils, so that the peptide chain can bind to the receptor on the surface of neutrophils and have anti-inflammatory activity. Formyl-Met-Acc⁶-Phe-OH replaced by Acc⁶ has stronger biological activity. Polypeptide analogues synthesized from cyclic amino acids are many times more active than the parent peptide. In addition, NMR and modeling studies showed that polypeptide analogues synthesized using cyclic amino acids were more likely to form β -rotation in solution, and were more easily recognized by neutrophil receptors and had better drug activity.

3. Antidiuretic activity

At the same time, Acc⁶ can also be used in the study of antidiuretic active drugs. For example: the use of Acc⁶ to replace the 2 or 3 amino acids of agonists of Arginine vasopressin (AVP) can play a role in narrowing blood vessels, promoting the rise of blood pressure and producing good antidiuretic activity. In addition, the introduction of configuration-limited nitrogenous acid Acc can reduce the flexibility of peptide chain and limit the degree of freedom of the conformation of peptide chain. Forcing peptide chains and residues into specific positions can prevent protein hydrolysis and increase protein stability.

4. Antitumor activity

Acc⁵ has the activity of inhibiting tumor growth. The tumor suppressor gene p53 is a multifunctional protein, which can regulate cell proliferation and inhibit the growth of cancer cells by inhibiting cell growth or causing cell apoptosis, DNA damage or stress stress.

When the glycine at the 7th position in the p53 protein polypeptide chain is replaced by Acc⁵, the p53 protein can more easily bind to the hydrophobic pocket of hdm2 receptor, thus strengthening the binding force with hdm2 receptor, better regulating the protein expression of p53 and inhibiting the growth of cancer cells.

5. Treatment of cardiovascular diseases

The introduction of cyclic amino acids into peptide sequences can make peptide sequences act as angiotensin converting enzyme (ACE) inhibitors and neutral endopeptidase (NEP) inhibitors. Cyclic amino acid modification of synthetic peptide sequences is useful for the treatment of diseases associated with ACE or NEP inhibitors, especially cardiovascular disorders such as hypertension, renal failure (including floating fibular and salt depletion), pulmonary edema, and congestive heart failure.

6. Cancer detection

Acc⁵ can be used in the diagnosis of cancer. For example, after injection of ¹¹C-labeled radioactive Acc⁵ for 1h, the accumulation of radioactive Acc⁵ in cancer cells was significantly higher than that in liver, and the distribution ratio between cancer cells and liver could reach 3:1.Using radioactive Acc⁵ for cancer cell detection found that Acc⁵ and cancer cells have a strong binding force, under X-ray diffraction, can be very good imaging, in the early diagnosis of brain tumor has a good prospect.

7. Others

Using Acc⁶ to replace Ala in tetradeceptide chain, tetradeceptide can be reduced to decapeptide, and the antibacterial activity of decapeptide can reach 8 ~ 10 times that of parent peptide. At the same time, cyclic amino acids can also be used as fungicides and sweeteners.