The Development of Novel Antibiotics Using ... - Jacobs University

Introduction
following protonation. An advantage of the carbon-nitrogen double bond of imine is its ability to
undergo reduction to the corresponding amine, which is more kinetically stable and offer a good
opportunity for the analysis of products from imine exchange reactions. An interesting example
for the formation of a small dynamic library of interchanging imine macrocycles has been
demonstrated by Wessjohann and co-workers (Figure 1.3). 10 Wessjohann et al. introduced an
innovative approach for quenching the imine exchange reaction based on Ugi four component
reactions as an alternative to the typical reduction procedure with borohydrides. 10 The quenching
process takes place by addition of an isocyanate and a carboxylic acid with stirring the mixture at
room temperature. The authors demonstrated that addition of Mg II followed by subsequent
quenching resulted in amplification of macrocyle 8 obtained through a [1+1]-cyclocondensation
reaction at the expense of the products obtained through [2+2]-cyclocondensation reactions,
while addition of Ba II , which has larger radius, resulted in formation of all library members
without preferential amplification.
Figure 1.3 A small DCL formed by reacting diamines 5 and 7 with dialdehyde 6.
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