AEEA-AEEA کے جوڑے کی کارکردگی اور ضمنی رد عمل کا کنٹرول

سالڈ فیز پیپٹائڈ سنتھیسز (SPPS) پیپٹائڈس یا پیپٹائڈ کی تیاری کے لیے مرکزی دھارے کا طریقہ ہے جیسے AEEA-AEEA تسلسل پر مشتمل مالیکیول۔ اس حقیقت کی وجہ سے کہ AEEA-AEEA ایک غیر قدرتی ڈائیپٹائڈ یونٹ ہے، اس کا جوڑنے کا رویہ اور ضمنی رد عمل کا پروفائل قدرتی امینو ایسڈ سے مختلف ہے اور اس کے لیے خصوصی اصلاح کی ضرورت ہے۔
Coupling efficiency optimization: In standard Fmoc SPS, AEEA-AEEA is added in the form of Fmoc AEEA-AEA-OH. Recommended coupling conditions: 4-fold excess, HATU (4-fold)/DIEA (8-fold) activation, DMF solvent, reaction at room temperature for 30-60 minutes. Kaiser testing shows that the first round coupling rate is usually>99%. However, it should be noted that when AEEA-AEEA is attached to the resin, the amino group of the second AEEA may exhibit reduced reactivity due to the formation of a hexagonal ring structure through intramolecular hydrogen bonding. Solution strategy: ① Extend the coupling time to 1 hour; ② Use double equivalent (8 times) of activated ester; ③ Add 0.1 M LiCl to break hydrogen bonds. Microwave assisted SPPS (50 ℃, 25 W, 10 minutes) can further improve efficiency to>99.5%.
Side reaction control: The main side reactions include: ① Formation of diketopiperazine (DKP): When the C-terminus of AEEA-AEEA is Pro or Gly, the amino group undergoes cyclization with the carbonyl group of the previous residue after Fmoc removal. Prevention: Immediately introduce amino acids with high steric hindrance (such as Ile and Phe) after AEEA-AEEA coupling, or deprotection with low alkaline concentration (2 eq DIEA). ② Aspartame rearrangement: If Asn or Asp is attached after AEEA-AEEA, rearrangement may occur under alkaline conditions. Countermeasure: Shorten the deprotection time (3 × 1 minutes) and add 0.1 M HOBt as a scavenger. ③ Ether bond cleavage: PEG containing segments may undergo ether bond cleavage during TFA cleavage, especially in the presence of strong acid scavengers such as TMSBr. Recommended cracking solution: TFA/TIS/H ₂ O=95:2.5:2.5, 2 hours, ice bath. By correctly controlling the above parameters, the crude purity of the target product can reach 85-90%, and after purification by preparative HPLC, the final purity is>98%.