N-(Benzyloxycarbonyloxy)succinimide (Cbz-OSu)

Technical Specifications

Product Description & Scientific Applications

Cbz-OSu (N-(benzyloxycarbonyloxy)succinimide, Z-OSu, benzyl N-succinimidyl carbonate) is the N-hydroxysuccinimide carbonate of benzyl alcohol and the common reagent for carboxybenzyl protection of amines. It is a crystalline solid melting at 80–82 °C, soluble in common organic solvents, and moisture-sensitive.

The Cbz group is transient: it is installed so the amine can be liberated later by mild hydrogenolysis. It is orthogonal to Boc, the two belonging to independent classes removed by different mechanisms, so either can be taken off first. On a Boc- and Cbz-protected protein, aqueous trifluoroacetic acid removes the Boc and leaves the Cbz groups in place.

Applications and Reactions

• Amine protection: Reacts with primary and unhindered secondary amines under mild base, with potassium carbonate in water and tetrahydrofuran, or triethylamine in dichloromethane, among the reported conditions. Bulky amines and anilines give low yields or no product.
• Protected amino acids: Converts amino acids to their Z-protected forms, valine to Z-valine among them, by a procedure amenable to both small and large scale.
• Selective amine capping on proteins: On a recombinant ubiquitin carrying one genetically encoded Boc-lysine, the six remaining lysine amino groups and the N-terminal amine are Cbz-capped in basic dimethyl sulfoxide. Aqueous trifluoroacetic acid then removes only the Boc, leaving a single free amine, and selective coupling at that site gives a native isopeptide bond.
• Protecting-group exchange: Where a Boc group must be replaced by Cbz, the Boc is stripped with trifluoroacetic acid and the Cbz installed with this reagent.
• Acid stability of the installed group: On benzyloxycarbonyl-lysine, the first-order deprotection rate rises a thousandfold between 2% and 50% trifluoroacetic acid in dichloromethane at 20 °C, so the group survives mild acid and is cleaved by strong.
• Medicinal chemistry intermediates: Used to protect the amine of an amino diol en route to a potent human renin inhibitor.
• Difficult substrates: On one aminopyridine the reagent required a much higher temperature and a stronger base and gave low selectivity; reductive cleavage of that carbamate with lithium aluminium hydride then gave the methylated aminopyridine in 82% yield.

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