Different substances such as dimethyl sulfoxide, tetramethylene sulfoxide, 2-pyrollidone, and the naturally occurring compatible solute betaine enhance PCR amplification of GC-rich DNA templates with high melting temperatures. In particular, cyclic compatible solutes outperform traditional PCR enhancers. We therefore investigated the effects that cyclic naturally occurring ectoine-type compatible solutes and their synthetic derivatives have on melting temperature of double-stranded DNA (dsDNA) and on PCR amplification of different templates. L-Ectoine, betaine, and derivatives Of L-ectoine decreased, whereas beta-hydroxyectoine increased, the melting temperature of dsDNA. The ability to decrease the melting temperature was greatest for homoectoine, a new synthetic derivative Of L-ectoine. Furthermore, compatible solutes, especially homoectoine, enhanced PCR amplification of GC-rich DNA (72.6% GC content; effective range: 0.1-0.5 M). (C) 2004 Elsevier Inc. All rights reserved.