Tyrosine Methyl Ester → HCID 131721855, compound

Participants

Reaction Steps

Solution Phase Couplings with Ddz-Xxx-Pfp and Ddz-Xxx-ODhbt. The efficiency of acylation of ODhbt esters, in terms of both coupling and racemization, was examined through the acylation of a simple amino acid alkyl ester, i.e., the acylation of H-Tyr-OMe with Ddz-L-Val-Dhbt and Ddz-D-Val-ODhbt in DMF at 0.1M. The dipeptides Ddz-L-Val-Tyr-OMe and Ddz-D-Val-Tyr-OMe were obtained in high yield (>90%) after a simple extractive workup and the Ddz-L-Val-Tyr-OMe gave a clean, single peak HPLC trace. Ddz-D-Val-ODhbt was not obtained as a solid, as it was contaminated with 5% of the azidobenzoate impurity, as mentioned by Atherton, et al.,54 which showed up in the HPLC trace. Both dipeptides gave clean 1H-NMR spectra. The attempted separation of the diastereomeric dipeptides by HPLC was unsuccessful over a wide range of isocratic gradients. In the 1H-NMR spectra, however, there is a slight difference in shift of the Val α-CH between the two dipeptides, hence there is no evidence in either spectra of any measurable amount of racemization.

Provenance & Evidence