Arginine-rich peptides isan important category oftherapeutic peptides coveringdifferent indications such ascancer, anti-infectious diseasesas well as drug delivery systems(several cell penetratingpeptides contain arginines intheir sequences).The work-up after synthesisof peptides containingunprotected arginine residuescan be very troublesome dueto the low solubility in organicsolvents. However, theirtetraphenylborate (TPB) salt isinsoluble in water but soluble ina wide range of organic solvents, allowing an extractive and costeffective work-up (Scheme 1).TPB is introduced as sodium tetraphenylborate to an aqueoussolution of a water-soluble salt of an arginine-containing peptide.The formed TPB salt precipitates and can be recovered byfiltration or extraction. When recovered as solid, TPB salts are verystable and can easily be stored. When recovered in solution theycan directly be engaged in the next process step with or withoutprior ion-exchange. This proprietary technology is not limited tofragments containing only one arginine residue, and can thusalso be applied for the synthesis of oligo- and polyarginines.The utility of the TPB technology is well-illustrated by thesynthesis ...