• Lee, J.H., et al.: Biosci., Biotechnol., Biochem., 68, 714 (2004)
• Lai, J.H., et al.: J. Med. Chem., 50, 2391 (2004)
• The Pf ester has also been developed for protection of the -carboxy group of glutamic acid in peptide synthesis, with better stability than trityl, but readily cleaved by TFA in DCM: Synlett, 1136 (1999).
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Reagent for protection of amines as their N-9-phenylfluorenyl (Pf) derivatives, which are ca 6000x more stable than trityl (Trt) groups (see Chlorotriphenylmethane, A11799) to acid hydrolysis: J. Chem. Soc., 1895 (1964), and have been found useful in asymmetric syntheses. The group has been introduced using K3PO4 or Et3N as base and Pb(NO3)2 as a bromide scavenger: J. Org. Chem., 50, 1239 (1985); 51, 3882 (1986). An alternative lead-free method uses K3PO4 and nitromethane: J. Org. Chem., 58, 2369 (1993). The Pf group can be cleaved with TFA in acetonitrile. For examples and discussion, see: Org. Synth. Coll., 9, 344 (1998). Hydrogenolysis: J. Org. Chem., 60, 4602 (1995); 61, 9437 (1996), or Li/ammonia reduction: J. Org. Chem., 55, 3511 (1990) have also been reported. N-Pf- and N-Trt- derivatives of amino acids have also been converted to Leuchs' anhydrides by treatment with phosgene or triphosgene, and the products coupled with amino acid esters to give dipeptides in good yields without racemization: J. Org. Chem., 64, 2532 (1999).
腐蚀性 (C)