Getting to Know Fmoc-Lys(Mtt)-Wang Resin (100–200 Mesh)
If you’re diving into more advanced peptide syntheses, you’ll eventually come across Fmoc-Lys(Mtt)-Wang Resin. It's a super useful tool, especially when you need a protected lysine sitting at the C-terminus of your peptide — and when you want side-chain flexibility later on.
Let’s unpack what it’s all about
What Is Fmoc-Lys(Mtt)-Wang Resin?
Breaking the name down:
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Fmoc: Protects the α-amine of lysine during peptide chain elongation.
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Lys(Mtt): You’ve got a lysine residue where the side-chain ε-amine is protected with an Mtt group (4-methyltrityl).
→ Mtt is special because it’s acid-labile but milder than other protecting groups — you can selectively remove it without touching the main chain! -
Wang resin: A polystyrene resin functionalized with a Wang linker, allowing for TFA cleavage at the end.
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100–200 mesh: Refers to particle size. This range (~75–150 μm) is standard for peptide synthesis, providing a good surface area and resin swelling properties.
What It’s Used For
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Solid-phase peptide synthesis (SPPS) where you want lysine at the C-terminus.
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Orthogonal protection strategies — since you can remove the Mtt group mid-synthesis without disturbing the Fmoc protection or cleaving the peptide off the resin.
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Great for making branched, cyclic, or modified peptides where side-chain manipulation is needed.
How It Works in Practice
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Deprotect Fmoc with piperidine → frees the α-amine.
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Build the peptide chain as usual.
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Optionally deprotect the Mtt group (using dilute TFA in DCM, usually 1–3% TFA) mid-synthesis to functionalize the lysine side chain.
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Cleavage from resin with strong TFA (typically ~95% TFA) after synthesis is complete.
Mtt Side-Note: Be cautious—Mtt deprotection releases colored byproducts (yellow-orange). You’ll see it happening!
Storage & Handling
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Keep dry and protected from light.
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Store under nitrogen or argon if possible.
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Pre-swell in DCM, DMF, or NMP before synthesis for best results.
Quick Tips
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Check loading: Knowing your resin’s loading (~0.4–0.7 mmol/g typically) helps in calculating accurate equivalents.
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Use fresh solvents: Moisture or degraded DMF can mess with coupling efficiency.
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Plan for Mtt removal: Have a plan ready if you need to functionalize the lysine side chain.
Final Thoughts
Fmoc-Lys(Mtt)-Wang Resin is a real game-changer if you’re working with more sophisticated peptide architectures. It gives you the power to modify the side chain independently from the main chain — a perfect setup for peptides with multiple functional handles.
Master it, and you’ll unlock a whole new level of peptide creativity.
Would you like me to also sketch out a simple workflow diagram showing how this resin is used during synthesis? (I can make it visual if you want!