Applications of BOP reagent in solid phase synthesis. Advantages of BOP reagent for difficult couplings exemplified by a synthesis of [Ala 15]-GRF(1-29)-NH2.
Fournier. A A; Wang. C T CT; Felix. A M AM
Key Findings
- BOP reagent gives faster, more complete couplings than DCC and other activation methods.
- Single‑coupling cycles with 3 equiv BOP and Boc‑amino acids are sufficient for most residues, improving yield and purity.
- Unprotected hydroxy‑amino acids (including Tyr) can be coupled with BOP, but only for fewer than 10 subsequent cycles.
Practical Outcomes
- For DIY peptide makers, switching to BOP in solid‑phase synthesis of GRF‑1‑29 can reduce the number of coupling steps and boost overall yield. Most residues can be added in one go, though Asn may still need a double coupling. When using unprotected hydroxy‑amino acids, keep the total number of subsequent cycles low to maintain product quality.
Summary
The study shows that using the BOP chemical reagent makes it easier and faster to build the GRF‑1‑29 peptide on a solid support compared to older methods like DCC. Most amino acids can be added in a single step, giving higher yields and good purity, while a few tricky spots (like Asn) still need extra steps. The method also works with unprotected hydroxy‑amino acids and tyrosine, but only for a short number of cycles.
Abstract
The BOP reagent [benzotriazol-l-yl-oxy-tris-(dimethylamino)phosphonium hexa-fluorophosphate] introduced by Castro et al. [Tetrahedron Lett. (1975) 14, 1219-1222] is ideally suited for solid phase peptide synthesis. The rate of coupling using BOP compared favorably to DCC and other methods of activation including the symmetrical anhydride and DCC/HOBt procedures. BOP couplings using the solid phase procedure proceeded more rapidly and to a greater degree of completion for peptide bond formations that were previously determined to be very slow using the conventional DCC method. Stepwise solid phase peptide synthesis using BOP was successfully utilized for the preparation of the (22-29) and (13-29) fragments of [Ala15]-GRF(1-29)-NH2. Single couplings with 3 equiv. BOP and Boc-amino acids and 5.3 equiv. of diisopropylethylamine in DMF were used for each cycle. The yields of the fragments were superior and the purities comparable using the BOP procedure (single couplings) to those observed using multiple couplings via the DCC coupling method. A total synthesis of [Ala15]-GRF(1-29)-NH2 was also carried out using the BOP procedure (single couplings and 3 equiv. BOP and Boc-amino acids and 5.3 equiv. diisopropylethylamine in DMF for each cycle). Multiple couplings were only required for Boc-Asn-OH due to the proposed formation of Boc-aminosuccinimide during activation. The resultant GRF(1-29) analog was comparable to a control prepared with multiple DCC couplings under optimized conditions. In a parallel study, unprotected Boc-(hydroxy)-amino acids were successfully coupled with the BOP reagent. However, the number of coupling cycles after the introduction of unprotected hydroxy-amino acid must be minimal (less than 10). The use of the BOP reagent with unprotected Tyr in solid phase peptide synthesis was also clearly established.
Study Information
pubmed
1988
10.1111/j.1399-3011.1988.tb00010.x