972 Bull. Chem. Soc. Jpn., 77, No. 5 (2004)
Hydrothermal Synthesis of Triglycine
ing trans-GG and cis-GG formation, but also by directly form-
ing cis-GG at 200 ꢁC. Thus, under hydrothermal conditions, G
and other types of amino acids may polymerize efficiently
through the formation of DKPs consisting of various amino
acids and the condensations of such DKPs and various amino
acids/oligopeptides. It is noteworthy that Nagayama et al.27 re-
ported that the larger the number n of (Gly)n in the condensa-
tion reaction with DKP, the higher the yield of the resulting
peptide, (Gly)nþ2. Thus, DKPs might enhance abiotic polymer-
ization more rapidly as the elongation proceeds in hydrother-
mal environments. This possibility should be investigated in
more detail in the future.
Fig. 9. Hypothetical reaction network, including G, cis-GG,
trans-GG, and DKP.
We thank Tomohiko Yamaguchi, Toshinori Kusumi, and
Hajime Mita for their technical suggestions. We are grateful
to Kazuhiro Iida and Shigeru Deguchi for their useful com-
ments and to Masatake Akita for drawing the diglycines. We
deeply appreciate Hirotaka Sugawara, director general of the
National Laboratory for High Energy Physics, for giving us
the opportunity to perform experiments there. This research
was financially supported by the Group Research (Soken/
G-3) Fund of the Graduate University for Advanced Studies.
Fig. 10. Probable mechanism of the reaction DKP + G !
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ꢁ
ed peptide formation, i.e., reaction a4, at 90 C. They investi-
gated the reaction of alanine with DKP, and the resulting tripep-
tide was NH2–Gly–Gly–Ala–COOH, not NH2–Ala–Gly–Gly–
COOH. Thus, they concluded that the reaction proceeds
through the nucleic attack of an amino group of monomeric
amino acids on DKP accompanied by its ring opening
(Fig.ꢁ 10). We expect that the same mechanism proceeds at
200 C, which will be confirmed by a future experiment em-
ploying Ala and DKP.
In this investigation, we confirmed that G polymerization
mediated by DKP occurs at 200 ꢁC as well as at 90 ꢁC.27 Since
DKP has been considered to be a chemically inactive and use-
less compound, its formation has been believed to be an un-
avoidable obstacle for the elongation of peptide chains beyond
dipeptides. However, we suggest that DKP is not a very stable
molecule, but serves as a probable intermediate for prebiotic
peptide formation under hydrothermal conditions. Moreover,
we suggest that the formation of DKP proceeds not only follow-