Study On The Synthesis Of Optically Active Dipeptides And Its Application To Asymmetric Cyanohydrination

Optically active cyanohydrin is one of the very important intermediates in agrochemical and pharmacy industry. Being one of the main intermediates for synthesis of optically active pyrethroides, (S)-alpha-Cyano-3-phenoxy benzyl alcohol is getting more and more attention. Chiral cyclic dipeptide is an effective catalyst for asymmertric cyanohydrin synthesis. We have studied the process of preparation of Optically active cyclic dipeptides by condensation of N-terminal protected pheylalanine and C-terminal protected histidine, Pd/C catalytic hydrogenating and cyclizing. Their structures were elucidated by Elemental Analyses, IR and 1HNMR. The products were farther treated by fractional crystallized from different solvents or by filtered through silica and so on. Different processes have given the product different crystal forms which varied from white crystal to gray gel. Experiments were carried out by using dipeptides as catalyst for asymmetric addition of hydrogen cyanide to aldehyde to produce (S)-alpha-Cyano-3-phenoxy benzyl alcohol and then (S,S)-fenvalerate. The experiments showed that, under 0℃, with HCN as source of CN- and toluene as solvent, (S,R)-fenvalerate showed enantiomeric excess (e.e.) up to 72.8%. The catalytic property can be affected greatly by the solvent. Among various solvents examined, toluene seems to be the best solvent. In addition to the importance of the solvent effect, the aggregation of the dipeptides also affects the catalytic property. Those dipeptides precipitated from low-pole or non-pole solvents with an form to be a kind of amorphism or adulterated with carbamide performed better than those perfectly purified. The catalytic ability of active carbon supported dipeptides was also studied. The cyclo dipeptides supported by active carbon also showed good catalytic ability.