Also alternatively, the condensation of benzyloxycarbonyl-beta-alanine (VIII) with dimeric cystamine (IX) by the activated ester method gives the protected cystamine intermediate (X), which is finally deprotected with HBr in acetic acid.
The reaction of disulfide (I) with sodium azide in DMSO gives the bis azido derivative (II), which is finally reduced with PPh3 in THF/water to afford the target beta-alanine derivative. Alternatively, the condensation of N-(tert-butoxycarbonyl)-beta-alanine (III) with S-acetyl-cysteamine (IV) by means of DCC in ethyl acetate gives the bet-alaninamide (V), which is deacetylated by means of NaOMe in methanol to yield N-[N-(tert-butoxycarbonyl)-beta-alanyl]cysteamine (VI). The dimerization of (VI) by means of I2 in Ac-OH affords the protected cystamine derivative (VII), which is finally deprotected by means of TFA.