1. Preparative Method for Asymmetric Synthesis of ( S)-2-Amino-4,4,4-trifluorobutanoic Acid
Jianlin Han, Ryosuke Takeda, Xinyi Liu, Hiroyuki Konno, Hidenori Abe, Takahiro Hiramatsu, Hiroki Moriwaki, Vadim A Soloshonok Molecules. 2019 Dec 10;24(24):4521. doi: 10.3390/molecules24244521.
Enantiomerically pure derivatives of 2-amino-4,4,4-trifluorobutanoic acid are in great demand as bioisostere of leucine moiety in the drug design. Here, we disclose a method specifically developed for large-scale (>150 g) preparation of the target (S)-N-Fmoc-2-amino-4,4,4-trifluorobutanoic acid. The method employs a recyclable chiral auxiliary to form the corresponding Ni(II) complex with glycine Schiff base, which is alkylated with CF3-CH2-I under basic conditions. The resultant alkylated Ni(II) complex is disassembled to reclaim the chiral auxiliary and 2-amino-4,4,4-trifluorobutanoic acid, which is in situ converted to the N-Fmoc derivative. The whole procedure was reproduced several times for consecutive preparation of over 300 g of the target (S)-N-Fmoc-2-amino-4,4,4-trifluorobutanoic acid.
2. Asymmetric synthesis of (S)-α-(octyl)glycine via alkylation of Ni(II) complex of chiral glycine Schiff base
Bo Fu, Ryosuke Takeda, Yupiao Zou, Hiroyuki Konno, Hiroki Moriwaki, Hidenori Abe, Jianlin Han, Kunisuke Izawa, Vadim A Soloshonok Chirality. 2020 Dec;32(12):1354-1360. doi: 10.1002/chir.23281.
Over last decade, the use of Ni(II) complexes, derived from of glycine Schiff bases with chiral tridentate ligands, has emerge as a leading methodology for preparation of structurally diverse Tailor-Made Amino Acids, the key structural units in modern medicinal chemistry, and drug design. Here, we report asymmetric synthesis of derivatives of (S)-α-(octyl)glycine ((S)-2-aminodecanoic acid) and its N-Fmoc derivative via alkylation of chiral nucleophilic glycine equivalent with n-octyl bromide. Under the optimized conditions, the alkylation proceeds with excellent yield (98.1%) and diastereoselectivity (98.8% de). The observed stereochemical outcome and convenient reaction conditions bode well for application of this method for large-scale asymmetric synthesis of (S)-2-aminodecanoic acid and its derivatives.
