title: Retraction.
abstract: Optical properties of substituted piperidine containing natural quinolizidine-alkaloids--theoretical versus experimental study. Bojidarka Ivanova and Michael Spiteller, Natural Product Research, DOI: 10.1080/14786419.2012.676546 (2012). This article has been retracted at the request of the Publisher in consultation with the Editor due to concerns and issues relating to the authorship of the article.