Gonadorelin Acetate Peptide

Liquid phase synthesis gradually connects amino acids through a protective group strategy in solution, suitable for the synthesis of short polypeptide chains containing special structures such as disulfide bonds. The core lies in the selection and removal sequence of protective groups to avoid side reactions.

Deprotection and purification:
Using TFA to remove Boc groups and pyridine to remove Fmoc groups, linear peptide PyrHisTrpSerTyrGlyLeuArgProGlyNH2 was obtained.
Purification by HPLC and freeze-drying to obtain crude Gonarelin.

Advantages: Accurate control of reaction conditions, suitable for complex peptide chain synthesis; No need for solid phase carriers, reducing costs.
Limitations: The steps are cumbersome and require multiple purifications; The reaction intermediates need to be purified to extend the production cycle.

A certain study used liquid-phase synthesis method to optimize the cutting reagent formula (88% TFA+5% anise sulfide+5% water+2% ethanedithiol), which increased the crude yield to 91.8% and the product purity to over 99%.

The molecular formula of Gonarelin Acetate is C ₅₇ H ₇₉ N ₁₇ O ₁₅, with a molecular weight of 1242.36 Da. Its core structure is a decapeptide chain, consisting of the following amino acid sequences:

5-Oxopropyl-L-Histoyl-L-tryptophan-L-tryptophan-L-tryptophan-L-tyrosyl-glycyl-L-leucyl-L-arginil-L-prolyl-glycinamide.
In this structure, the first 5-oxoproline (Pyroglutamic acid) forms a cyclic structure, enhancing molecular stability; Glycine (Gly) at position 6 and glycinamide (Gly-NH ₂) at position 10 are flexible segments that endow the molecule with conformational flexibility; The third tryptophan (Trp) and fifth tyrosine (Tyr) contain aromatic rings and may participate in intermolecular interactions through π - π stacking.
The introduction of acetate form (CH3 COO ⁻) not only enhances the solubility of the drug (with a water solubility of up to 25 mg/mL), but also binds to the amino or carboxyl groups of the chain through ionic bonds, forming a stable salt structure and reducing the risk of peptide chain degradation during storage.

The ability of hydroxyl, amino, carboxyl groups to form hydrogen bonds with water molecules requires storage in a dry environment to avoid clumping or degradation.
Solubility:
This compound has a high solubility in water (25 mg/mL), is slightly soluble in methanol, and can be completely dissolved in 1% acetic acid solution. Its solubility is significantly affected by pH: under acidic conditions (such as 1% acetic acid), carboxyl protonation reduces intermolecular electrostatic repulsion and promotes dissolution; In neutral or alkaline environments, deprotonation of carboxyl groups may trigger intermolecular aggregation, leading to a decrease in solubility.

Melting point and thermal stability:
Experimental data shows that the melting point is higher than 155 ° C (decomposition), indicating strong thermal stability. However, high temperatures may cause peptide bond hydrolysis or amino acid side chain oxidation, so actual storage needs to be controlled within the range of -20 ° C to 8 ° C to delay degradation.

Spectral characteristics:
The UV absorption spectrum shows a maximum absorption peak at 278 nm, corresponding to the aromatic ring conjugated system of tryptophan and tyrosine. This feature can be used for quantitative analysis (such as spectrophotometric determination of content), or for comparing purity with reference standards through thin layer chromatography (TLC).

HYDROLYTIC STABILITY
Relatively stable under acidic or neutral conditions, but prone to peptide bond hydrolysis in alkaline environments. For example, under the action of strong bases (such as NaOH), the peptide bond between the 6th glycine and the 7th leucine may break, generating short peptide fragments. In addition, the indole ring of the third tryptophan is prone to ring opening under light or oxidative conditions, leading to loss of drug activity.

In the presence of oxygen or free radicals, these functional groups may undergo oxidation reactions, generating peroxides or hydroxyl derivatives, which in turn trigger chain degradation. Therefore, antioxidants (such as vitamin C) are often added to formulations to enhance stability.

Light stability
Sensitivity to light, especially ultraviolet light (200-400 nm), may directly disrupt the conjugated system of tryptophan or indirectly trigger oxidative degradation through the generation of free radicals. Clinical injections should be packaged in brown glass bottles and stored away from light.

Receptor binding activity
By binding with high affinity to the GnRH receptor in the anterior pituitary gland through its ten structure, intracellular signaling (such as the cAMP/PKA pathway) is triggered, leading to the release of gonadotropins (FSH, LH). Its binding activity depends on:
The complementarity between the cyclic structure of the first 5-oxoproline and the receptor pocket;
The π - π interaction between the aromatic ring of the third tryptophan and the hydrophobic region of the receptor;
The positive charge of the 8th arginine is electrostatically attracted to the acidic residue of the receptor.

Biphasic mechanism
When administered continuously in the short term, it stimulates the release of FSH/LH from the pituitary gland and increases the levels of sex hormones; Long term administration leads to inhibition of FSH/LH secretion due to receptor desensitization, ultimately reducing sex hormones to castration levels. This characteristic makes it an alternative to surgical castration in the treatment of prostate cancer, while reducing the risk of surgical complications.

Polymorphic degradation products:
During the metabolic process in the body, various metabolites may be generated through enzymatic hydrolysis (such as peptidase action) or non enzymatic degradation (such as oxidation). For example, the 6th glycine may be hydrolyzed to generate a nine peptide fragment; The oxidation of tryptophan in the third position generates hydroxyl derivatives. The activity of these metabolites needs to be identified by mass spectrometry (LC-MS) or nuclear magnetic resonance (NMR) to evaluate their safety.
Drug interactions:
When used in combination with drugs containing metal ions (such as certain antibiotics), the solubility or activity of gonadorelin acetate peptide may be reduced due to chelation. In addition, its acidic salt form may undergo neutralization reactions with alkaline drugs (such as antihistamines), and mixed injections should be avoided.