Biologically active compounds are provided that can be used as photosensitizers for diagnostic and therapeutic applications, particularly for PDT of cancer, infections and other hyperproliferative diseases, fluorescence diagnosis and PDT treatment of a non-tumorous indication such as arthritis, inflammatory diseases, viral or bacterial infections, dermatological, ophthalmological or urological disorders as well as providing methods to obtain them in pharmaceutical quality. One embodiment consists of a method to synthesize a porphyrin with a defined arrangement of meso-substituents and then converting this porphyrin system to a chlorin system by dihydroxylation or reduction, and if more than one isomer is formed separate them by chromatography either on normal or reversed phase silica. In another embodiment the substituents on the porphyrin are selected to direct the reduction or dihydroxylation to the chlorin so that a certain isomer is selectively formed. Another embodiment is to provide amphiphilic compounds with a higher membrane affinity and increased PDT-efficacy. In another embodiment a method to reductively cleave the osmate(VI)ester avoiding the use of gaseous H2S is provided. In another embodiment substituents are identified that via their steric and/or electronic influence direct the dihydroxylation or reduction with diimine so that one isomer is favored. Another embodiment consists of formulate the desired isomer into a liposomal formulation to be injected avoiding undesirable effects like solubility problems or delayed pharmacokinetics of the tetrapyrrole systems.