Protecting groups: on and offTwo groups block an amine, Cbz and Boc; two block an acid, the methyl and the benzyl ester. Draw what each reaction makes, and what it leaves behind.

Cbz on glycine: Benzyl chloroformate turns glycine’s amine into a carbamate, in water with sodium hydroxide. Draw the intermediate, then the product.

Cbz off, with hydrogen: Hydrogen on palladium cuts the benzylic C–O bond of a Cbz group. Draw the three pieces, in the order they appear.

Boc on alanine: Di-tert-butyl dicarbonate puts a Boc group on alanine’s amine, with triethylamine as the base. Draw the protected amino acid, then the alcohol formed.

Boc off, with acid: Trifluoroacetic acid takes a Boc group off at room temperature. Draw the cation that leaves, the gas it becomes, and the amino acid.

Methyl ester of phenylalanine: Thionyl chloride in methanol esterifies the acid of phenylalanine. Draw the methyl ester.

Methyl ester off, with lithium hydroxide: Lithium hydroxide hydrolyses a methyl ester and leaves the Boc group alone. Draw the intermediate, the carboxylate and the alcohol released.

Benzyl ester of alanine: An O-benzyl isourea turns alanine’s acid into a benzyl ester. Draw the ester, then the urea left behind.

Benzyl ester off, with hydrogen: Hydrogen on palladium cuts a benzyl ester as it cuts a Cbz group, and leaves a Boc group alone. Draw the two products.

Draw the products and intermediates of a peptide synthesis, from protecting groups to DCC coupling, and follow two slide shows. The exercises need JavaScript, because every drawing is checked in your browser.

Why protect — heat two amino acids, and count what forms

Protecting groups — put them on, take them off

Coupling with DCC — activate the acid, then form the amide

Planning a synthesis — protect, couple, deprotect, in the right order

Builder — type a sequence, see the molecule

Cheatsheet — every group, how it goes on and comes off

Talks — two slide shows, mechanisms included

About — what the site is, and how to cite it

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