Amino protecting groups with trityl function

In subsequent studies,22 Sheehan et al. demonstrated that the action of diisopropylcarbodiimide on penicilloate 24, prepared by protection of the free primary amino group in 23 with trityl chloride (see Scheme 6b), results in the formation of the desired -lactam 25 in a very respectable yield of 67 %. In this most successful transformation, the competing azlactonization reaction is prevented by the use of a trityl group (Ph3C) to protect the C-6 amino function. Hydrogenolysis of the benzyl ester function in 25, followed by removal of the trityl protecting group with dilute aqueous HC1, furnishes 6-aminopenicillanic acid (26), a versatile intermediate for the synthesis of natural and unnatural penicillins. 

The aziridine 12i has been derived from the trans amino alcohol 12h by the two-step, one-pot process i) selective protection of the amino functionality with trityl chloride and ii) mesylation of the hydroxyl in the presence of triethylamine. Under these conditions, the mesylate intermediate has been converted to aziridine 12i. Treatment of 12i with /-pentyl alcohol in the presence of 1.5 equiv of BF3-Et20 followed by acetylation of the crude product provides the ether 121. Finally, reduction of the azide functionality and saponification of the ester group in 121 give GS4071,12. 

The p-methoxytrityl and to a lesser extent the trityl function are currently used primarily as protecting groups for the primary 5 -hydroxyl of nucleosides. Under mild reaction conditions, only minor tritylation of a secondary hydroxyl or base amino function will occur. If it seems surprising that tritylation of the exocyclic amino function is difficult, especially since the trityl group has been noted to be useful for the protection of the amino function of amino acids, it should be remembered that the base amino function (with its delocalized nonbonding electron pair) is significantly less nucleophilic than a primary alkyl amine. The secondary hydroxyl(s) will... 

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