合成路线1

The modified tyrosine building block (II) was prepared by alkylation of N-Cbz-L-tyrosine (I) at both the phenolic OH and the NH groups employing dimethyl sulfate under phase-transfer conditions. N-Boc-L-Threonine benzyl ether (III) was converted to the corresponding (triethylsilyl)ethoxymethyl ester, and the O-benzyl group was subsequently removed by catalytic hydrogenolysis to afford (IV). Coupling between the tyrosine (II) and threonine (IV) derivatives using DCC and DMAP gave rise to the protected didepsipeptide (V). The SEM protecting group was then cleaved by means of HF in acetonitrile, yielding intermediate (VI)