9-Fluorenylmethyl Choroformate: A Versatile Reagent for Peptide Synthesis？ ¹

9-Fluorenylmethyl Choroformate, also known as Fmoc-Cl or 9-fluorenylmethyl chloroformate, is a reagent commonly used in peptide synthesis and derivatization for amino acid and amine protection. It has the molecular formula C15H11ClO2 and a molecular weight of 258.70. Fmoc-Cl is a white crystalline solid with a melting point of 62~64 oC and is soluble in organic solvents such as CH2Cl2, THF, and dioxane. However, it should be handled with caution as it is moisture-sensitive, corrosive, and can cause severe irritation to the skin and eyes.

One of the main applications of Fmoc-Cl is the protection of the N-terminus of amino acids. It can be used in conjunction with sodium bicarbonate or sodium carbonate as a base in solvents such as dioxane and DMF/water mixture to protect amino acids and similar compounds. The Fmoc protecting group can be removed by treatment with 20%~30% piperidine in DMF. Unlike other protecting groups, Fmoc protection does not require the use of harsh acids such as HF or trifluoroacetic acid.

Protecting Amines and Hydroxyl Groups

Fmoc-Cl can also be used for the protection of primary and secondary amines, similar to the protection of amino acid N-termini. The reaction conditions are generally the same as those used for amino acid protection.

Protection of Amines and Hydroxyl Groups in Nucleosides, Sugars, and Natural Products

Fmoc-Cl is also employed for the protection of amino groups in various nucleosides, including adenosine, cytidine, guanosine, and their corresponding 2'-deoxy derivatives. It can also be used for the protection of hydroxyl groups in sugars (as shown in the figure below).

Fmoc derivatives are widely used in fluorescence detection and analysis. Fmoc-protected amino acids and other primary and secondary amines can be analyzed by HPLC, taking advantage of their high UV sensitivity.

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