As a part of my Bachelor's thesis we aimed to prepare a part of a tetrapeptide
electrophilic probe, namely Arg(Boc)2-SerOMe (4). N-Cbz-Arg(Boc)2-OH (1) was
successfully synthesized from N-Cbz-Orn(Boc)-OH and N,N'-Boc2-Smethylisothiourea. Compound 1 was then coupled with serine methyl ester
hydrochloride to the dipeptide N-Cbz-Arg(Boc)2-SerOMe (2) in the presence of three
different coupling reagents: CDI, EEDQ and EDC. α-N-benzyloxycarbonyl-ω,ω'-di-N-tbutoxycarbonyl-L-arginine lactam (3) was formed as a by-product. An attempt to reduce
the proportion of compoud 3 was unsuccessful. As a last step in the synthesis of
compound 4, Cbz protecting group was selectively removed from compound 2 by
catalytic hydrogenation.
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