Synthese von [ D ‐Alanin 1 , 4′ ‐azido‐3′, 5′ ‐ditritio‐ L ‐phenylalanin 2 , norvalin 4 ]α‐melanotropin als «Photoaffinitätsprobe» für Hormon‐Rezeptor‐Wechselwirkungen

Synthesis of [ D ‐alanine 1 , 4′‐azido‐3′, 5′‐ditritio‐ L ‐phenylalanine 2 , norvaline 4 ]α‐melanotropin as a ‘photoaffinity probe’ for hormone‐receptor interactions. The synthesis of an α‐MSH derivative containing 4′‐azido‐3′,5′‐ditritio‐ L ‐phenylalanine is described: Ac · D ‐Ala‐Pap( 3 H 2 )‐Ser‐Nva‐Glu‐His‐Phe‐Arg‐Trp‐Gly‐Lys‐Pro‐Val · NH 2 . This hormone analogue is being used for specific photoaffinity labelling of receptor molecules. The synthesis was performed in a way to minimize the number of radioactive steps and to introduce the radio‐active and the photoaffinity label exclusively into position 2. The dipeptide N (α)‐acetyl‐ D ‐alanyl‐ (4′‐amino‐3′,5′‐diiodo)‐ L ‐phenylalanine was tritriated and transformed into the azido compound, N (α)‐acetyl‐ D ‐alanyl‐(4′‐azido‐3′,5′‐ditritio)‐ L ‐phenylalanine which was then condensed with H · Ser‐Nva‐Glu(O t Bu)‐His‐Phe‐Arg‐Trp‐Gly‐Lys(BOC)‐Pro‐Val · NH 2 to the tridecapeptide. The α‐MSH analog displayed a specific activity of 11 Ci/mmol, and a biological activity of about 4 · 10 9 U/mmol (10% of α‐MSH).