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Tautomeric Equilibria in 3‐Amino‐1‐(2‐aminoimidazol‐4‐yl)prop‐1‐ene, a Central Building Block of Marine Alkaloids
Author(s) -
Wei Yin,
Zipse Hendrik
Publication year - 2008
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200800294
Subject(s) - tautomer , chemistry , protonation , ab initio , gas phase , ab initio quantum chemistry methods , computational chemistry , block (permutation group theory) , medicinal chemistry , stereochemistry , molecule , organic chemistry , ion , geometry , mathematics
The tautomers I – IV of the marine metabolite 3‐amino‐1‐(2‐aminoimidazol‐4‐yl)prop‐1‐ene ( 1 ) were previously suggested to have rather similar stabilities.1,2 Through a series of DFT and ab initio calculations, their relative stabilities were investigated in both the gas phase and in water, and also compared to their Z‐isomers V – VIII . The tautomers I and III have almost identical stability in the gas phase and in water. The Z‐isomer VII is more stable than other tautomers in the gas phase and quite competitive with I and III in water. The tautomers II and IV are much less stable and unlikely to coexist in equilibrium with I and III . The calculated p K a of 1 ‐H + of +10.9 suggests that 1 is fully protonated even under mildly acidic conditions. Protonation decreases the stability difference between the most stable tautomer III and the less stable tautomer IV .(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)