Efficient stereocontrolled synthesis of sitagliptin phosphate

The synthesis of sitagliptin phosphate 1, a novel DPP-IV inhibitor for the treatment of type 2 diabetes mellitus has been accomplished starting from the chiral synthon (1,4-bis[(R)-1-phenylethyl]piperazine-2,5-dione) 2, involving highly stereocontrolled (>98%) alkylation as a key step, in a good overall yield of 50% over six steps.

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Sitagliptin phosphateC16H15F6N5O[α]D25.2 = −73.1 (c 0.13, H2O)Absolute configuration: (3R)Souce of chiralty: (R)-1- phenylethylamine

1,4-Bis[(R)-1-phenylethyl]piperazine-2,5-dioneC20H22N2O2[α]D23.4 = +342.0 (c 0.13, CHCl3)Absolute configuration: (1′R,1″R)Souce of chiralty: (R)-1- phenylethylamine

(3R,6R)-1,4-Bis[(R)-1-phenylethyl]-3,6-bis(2,4,5-trifluorobenzyl)piperazine-2,5-dioneC34H28F6N2O2[α]D24.6 = −36.7 (c 0.14, CHCl3)Absolute configuration: (1′R,1″R,3R,6R)Souce of chiralty: (R)-1- phenylethylamine

(R)-2-(tert-Butoxycarbonylamino)-3-(2,4,5-trifluorophenyl)propanoic acidC14H16F3NO4[α]D25.3 = −1.5 (c 0.12, CH3OH)Absolute configuration: (2R)Souce of chiralty: (R)-1- phenylethylamine

(R)-3-(tert-Butoxycarbonylamino)-4-(2,4,5-trifluorophenyl)butanoic acidC15H18F3NO4[α]D24.3 = +27.8 (c 0.13, CHCl3)Absolute configuration: (3R)Souce of chiralty: (R)-1- phenylethylamine

(R)-tert-Butyl 4-oxo-4-(3-(trifluoromethyl)-5,6-dihydro-[1,2,4]triazolo[4,3-a]pyrazin-7(8H)-yl)-1-(2,4,5-trifluorophenyl)butan-2-ylcarbamateC21H23F6N5O3[α]D25.1 = +20.8 (c 0.11, CHCl3)Absolute configuration: (3R)