decarbamoylation/ diazotization

Hello

I am trying to prepare D-Tyrosine from crresponding hydantion by using
enzyme called hydantoinase.After getting the N-carbamoyl D-aminoacid,
i have to do diazotisation by using NaNO2/HCl.there are many reports
in literature using this method.But when i tried for N-carbamoyl
D-tyrosine in acidic medium at temp0-5C using NaNO2, the yield is very
low(20%).
Can any body suggests is there any other route to improve the yield up
to 60-70%

thank you

Koteshwar
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