1. Inst. for Organic Chemistry and Biochemistry; Technische Universität Darmstadt; 64287 Darmstadt Germany
2. Merck Millipore, Pharm Chemical Solutions, Upstream Cell culture media R&D; Frankfurter Strasse 250 64293 Darmstadt Germany
3. Merck KGaA, PTD; Frankfurter Strasse 250 64293 Darmstadt Germany