N-Boc-D-alanine (I) was coupled to the resin using diisopropyl carbodiimide and 1-hydroxybenzotriazole to afford resin (II). Subsequent cleavage of the Boc protecting group by means of trifluoroacetic acid provided the D-alanine-bound resin ( III) Sequential coupling and deprotection cycles were carried out with the following protected amino acids:. N-Boc-L-proline (IV), N-alpha-Boc-N6-isopropyl-N6-carbobenzoxy-L-lysine (VI) and N-Boc-L-leucine (VIII) to afford the respective peptide resins (V), (VII) and (IX). N-alpha-Boc-D-4-(Fmoc-amino) phenylalanine (X) was coupled to (IX), yielding resin (XI). Cleavage of the side-chain Fmoc protecting group with piperidine in DMF gave the aniline derivative (XII). After conversion to the corresponding urea by treatment with tert-butyl isocyanate, the Boc group was cleaved with trifluoroacetic acid to produce resin (XIII).
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Bioorganic & Medicinal Chemistry

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Keywords: Synthesis. New drug molecules. New chemical entities. Medicine …Degarelix acetate (Firmagon®) . ….. Scheme 5. Synthesis of degarelix acetate (V).

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