Resin Loading¶

First Amino Acid Attachment¶

After selecting the appropriate resin, the first amino acid must be attached to the solid support.

What Are the Methods for Resin Loading?¶

Method 1: Symmetric Anhydride Activation¶

Best for Wang and similar resins with hydroxyl linkers.

1. Dissolve Fmoc-AA-OH (3 eq) in DCM
2. Add DIC (1.5 eq)
3. React 15 minutes at 0 °C
4. Add DMAP (0.1 eq) and resin
5. React 1–2 hours

Method 2: Pre-Activated Esters¶

Simpler, commercially available pre-activated amino acids.

1. Dissolve Fmoc-AA-OPfp or Fmoc-AA-ODhbt in minimal DMF
2. Add to swollen resin
3. React 1–2 hours

Method 3: HBTU/HATU Activation¶

Standard coupling reagents with DIEA base.

1. Fmoc-AA-OH (3 eq) + HBTU (2.9 eq) in DMF
2. Add DIEA (6 eq)
3. Add to resin
4. React 45–60 minutes

Loading Capacity Measurement¶

UV Method¶

1. Weigh accurately 5–10 mg of loaded resin
2. Add 1 mL of 20% piperidine/DMF
3. Incubate 20 minutes
4. Measure UV at 301 nm
5. Calculate: Loading = (Abs × Volume) / (ε × mass × path length)

Typical Loading Values¶

Capping¶

After loading, unreacted sites should be capped to prevent deletion sequences:

1. Add capping solution (Ac₂O + DIEA in DMF)
2. React 20–30 minutes
3. Wash thoroughly

4. Measure loading again to confirm

5. First Amino Acid Attachment — Review the section above for key parameters, methods, and quality criteria.

6. What Are the Methods for Resin Loading? — See the section for detailed parameters and specifications.
7. Loading Capacity Measurement — Review the section above for key parameters, methods, and quality criteria.

Key Takeaways¶

• First Amino Acid Attachment — Review the section above for key parameters, methods, and quality criteria.
• What Are the Methods for Resin Loading? — See the section above for detailed parameters and specifications.
• Loading Capacity Measurement — Review the section above for key parameters, methods, and quality criteria.

🔗 Related: SPPS Process | Coupling Reaction | Wang Resin | Rink Amide Resin