Two side‐reactions occur during the DCC‐mediated attachment of Fmoc‐amino acids to p‐alkoxybenzyl alcohol resins viz. dipeptide formation and racemization. The addition of 1‐hydroxybenzotriazole in combination with a low reaction temperature is shown to decrease both side‐reactions to an acceptable level without lowering the degree of incorporation.
The synthesis is described of several fragments of the neurohypophyseal nonapeptide hormones arginine vasopressin and oxytocin. One group of fragments is characterized by the presence of an asymmetrical disulfide (a cystine residue in position 6), a second group consists of dimeric (symmetrical disulfides) fragments.
As common intermediates, peptides containing an S‐tritylcysteine residue were synthesized by the fragment condensation approach. Treatment with methoxycarbonylsulfenyl chloride followed by reaction with the free thiol function of cysteine gave the asymmetrical disulfides, while treatment of the S‐tritylcysteine containing peptide with iodine resulted in the corresponding dimers. Peptides with an N‐terminal glutamine residue (position 4) were found to convert spontaneously into the corresponding pyroglutamic acid products.
Die Synthese der Titelverbindungen (VI), (VII), (XIa), (Xlc) (Arginin‐Vasopressin‐Fragmente) bzw. (IX), (XIb), (Xld) (Oxytocin‐Frag‐ mente) wird beschrieben.
The dangerous I iquid HF, which in addition causes many side-reactions, has successfully been replaced by the easy-to-handle organic acid methanesulfonic acid for the cleavage of smal I peptides from the standard Merrifield resin.
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