Biicherer-Bergs reaction

Amides, N-alkyl amides, lactams, hydantoins have been identified in both Murchison and Yamoto-791198 meteorites [63,65], confirming preliminary results from Cooper and Cronin [66]. The only peptides identified until now are diglycine and diketopiperazine (cyclic diglycine). Since only N1-unsubstituted hydantoins have been detected, this provides a good argument for the involvement of the Biicherer-Bergs reaction in their formation (cf. Sect. 2.1.4). 

Figure 1 Strecker and related systems complex network of equilibrium reactions from aqueous solutions of cyanide, ammonia, and aldehyde, 1. Pathways for exiting the equilibrated network correspond to (a) cyanohydrin hydrolysis, (b) aminonitrile hydrolysis, and (c) Biicherer-Bergs reaction. Adducts 6 and 7 and other hydrolysis products can be formed at high concentrations of reactants.

Since an important feature of Biicherer-Bergs hydantoin formation is that the process can only work for a-aminonitriles without substituent on the amino group, it follows that one compound of the equilibrium mixture formed from an aldehyde, ammonia, and cyanide is selectively reacted through an irreversible process leaving N-alkylated aminonitriles or imino-dinitriles unreacted. However, the difficulty with this process is that CAAs and hydantoins are poorly reactive towards hydrolysis and need long periods of time to be converted into free AAs. But, CAAs may also have per se a prebi-otic importance in activation pathways towards polypeptides (see Sect. 3.3.7). CAAs can also be synthesized by reaction of free amino acids with cyanic acid/cyanate (a likely prebiotic compound [50]). In the presence of a steady-state concentration of either cyanate or urea in aqueous medium, CAAs are at equilibrium with A A [51]. 

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