Synthesis of conformationally restricted serine derivatives through ruthenium(II)-catalyzed ring closing metathesis

The PAUSON-KHAND REACTION IN SYNTHESIS OF BICYCLIC RIGID Α-Amino ACIDS

“…11 Subsequent cyclization reactions by Pd(0)-catalysis or Ru(II)-RCM reactions have been found compatible with the bislactim moiety and have been highly useful for the construction of rigid cyclic a-amino acids. [6][7][8][9][10] In this report we show that cobalt complexes under the Pauson-Khand conditions are also compatible with the bislactim moiety and can become highly useful for the construction of bicyclic a-amino acids. The cyclopentenone ring moiety in the pentalene system 3 and 4 is inherently functionalized for further chemical transformations if desired.…”

“…Our efforts have largely been directed toward the development of stereoselective methodology for the preparation of rigid cyclic amino acids where the a-carbon of the amino acid is imbedded in the ring. [6][7][8][9][10] The chiral information required for the www.dekker.com preparation of these structures is available in the Scho¨llkopf bislactim auxiliary 1 as a substrate for stereoselective alkenylation and alkynylation. The bislactim ether 1 is derived from an enantiomerically pure diketopiperazine of valine and glycine.…”

Chemoselective rhodium(II)–carbenoid cyclisation reactions in the stereoselective construction of rigidified cyclic α-amino acid derivatives

“…HRMS: M 256.1781. C 13 3.80 and 3.92 (2H,2d,J 4.0 Hz,[2][3][4][5]m,CHOHCH 3 ), 5.38 (1H, br s, CHOH); d C (CDCl 3 ) 17. 1, 17.5, 19.3 and 19.5 (2 · CH(CH 3 ) 2 ), 23.4 and 23.6 (2 · CHOHCH 3 ), 25.9 and 29.8 (2 · CH 3 ), 31.1 and 31.4 (2 · CH(CH 3 ) 2 ), 47.6 and 49.0 (2 · CH 2 CHOH), 52.…”

“…[1][2][3][4] This work was initiated because it had been established that rigidified a-carbosubstituted a-amino acids play an important role in drug design and development, which involves small peptides and peptidomimetics. 5 The cyclic structures prepared are members of an important family of quaternary a-amino acids.…”

Homocoupling in the Preparation of Dimeric Cyclic Peptide Derivatives

“…104Ϫ106°C (MeCN). 1 A solution of (2R)-5-(3-butenyl)-2,5-dihydro-2-isopropyl-3,6-dimethoxypyrazine (6) [15] (0.476 g, 1.98 mmol) in anhydrous THF (5 mL) at Ϫ78°C was lithiated by the addition of a solution of nBuLi in hexane (1.4 mL, 1.44 , 2.2 mmol). The solution was stirred at Ϫ78°C for 30 min before a solution of 1,2-dibromo-(tetrafluoro)ethane (0.260 g, 0.12 mL, 1.00 mmol) in THF (2 mL) was added dropwise.…”