Solid Phase Peptide Synthesis

Solid Phase Peptide Synthesis (SPPS)

SPPS is the dominant method for constructing peptides in research settings. Developed by Bruce Merrifield in 1963 (Nobel Prize 1984), it revolutionized peptide chemistry by enabling automated, iterative assembly of amino acid chains on an insoluble polymer support.

Core Principle

The C-terminal amino acid is anchored to a solid resin. Subsequent amino acids are added stepwise to the N-terminus. Excess reagents are removed by simple washing.



Cycle: Deprotection → Coupling → Washing → [Repeat]

Two Main Strategies

Fmoc/tBu Strategy (Most Common)

Component	Details
<strong>Protecting Group</strong>	Fmoc (9-fluorenylmethoxycarbonyl)
<strong>Deprotection</strong>	20% piperidine in DMF, 2 x 10 min
<strong>Side Chain Protection</strong>	tBu (tert-butyl) esters and ethers
<strong>Cleavage</strong>	TFA cocktail (95% TFA + scavengers)
<strong>Final Product</strong>	Free acid (C-terminal COOH)

Coupling Reagents

Reagent	Activation Mechanism	Notes
<strong>HBTU/HOBt</strong>	Active ester	Classic, reliable
<strong>HATU/HOAt</strong>	Active ester	Higher efficiency, expensive
<strong>DIC/Oxyma</strong>	Active ester	Non-toxic alternative to HOBt
<strong>PyBOP</strong>	Phosphonium salt	Low racemization

Critical Parameters

Coupling Time: 30-60 minutes per residue

Excess Amino Acid: 2-4 equivalents

Racemization Control: Monitor epimerization-prone residues

Double Coupling: Recommended for difficult sequences

See [[Peptide Science Overview]], [[Amino Acid Reference]], [[HPLC Analysis]]

OUTGOING: [[Peptide Science Overview]] [[Amino Acid Reference]] [[HPLC Analysis]]

INCOMING: [[Peptide Modifications]] [[Laboratory Safety Protocols]] [[HPLC Analysis]] [[Amino Acid Reference]] [[Peptide Science Overview]]

# Solid Phase Peptide Synthesis (SPPS)

**SPPS** is the dominant method for constructing peptides in research settings. Developed by Bruce Merrifield in 1963 (Nobel Prize 1984), it revolutionized peptide chemistry by enabling automated, iterative assembly of amino acid chains on an insoluble polymer support.

## Core Principle

The C-terminal amino acid is anchored to a solid resin. Subsequent amino acids are added stepwise to the N-terminus. Excess reagents are removed by simple washing.

```
Cycle: Deprotection → Coupling → Washing → [Repeat]
```

## Two Main Strategies

### Fmoc/tBu Strategy (Most Common)

| Component | Details |
|-----------|---------|
| **Protecting Group** | Fmoc (9-fluorenylmethoxycarbonyl) |
| **Deprotection** | 20% piperidine in DMF, 2 x 10 min |
| **Side Chain Protection** | tBu (tert-butyl) esters and ethers |
| **Cleavage** | TFA cocktail (95% TFA + scavengers) |
| **Final Product** | Free acid (C-terminal COOH) |

## Coupling Reagents

| Reagent | Activation Mechanism | Notes |
|---------|---------------------|-------|
| **HBTU/HOBt** | Active ester | Classic, reliable |
| **HATU/HOAt** | Active ester | Higher efficiency, expensive |
| **DIC/Oxyma** | Active ester | Non-toxic alternative to HOBt |
| **PyBOP** | Phosphonium salt | Low racemization |

## Critical Parameters

1. **Coupling Time**: 30-60 minutes per residue
2. **Excess Amino Acid**: 2-4 equivalents
3. **Racemization Control**: Monitor epimerization-prone residues
4. **Double Coupling**: Recommended for difficult sequences

See [[Peptide Science Overview]], [[Amino Acid Reference]], [[HPLC Analysis]]