A ConvenientN-Protection of Pyroglutamate Derivatives

Synthesis of Variously Functionalized Azabicycloalkane Scaffolds by Domino Metathesis Reactions

7,5-Fused azabicycloalkane scaffolds, carrying a quaternary stereocenter at C3 position of the lactam ring, can act as effective reverse-turn mimics and have proven to be useful intermediates for the preparation of Arg-Gly-Asp (RGD)-based cyclopentapeptides (cRGD) with nanomolar activity as α_vβ₃/α_vβ₅ integrin antagonists. Here, we report the synthesis of new azabicycloalkane scaffolds endowed at the C6 position with a para-substituted phenethyl side chain, which could be exploited to obtain cRGD-based bioconjugates that may find promising applications in anticancer therapy. By performing a domino cross enyne metathesis/ring-closing metathesis (CEYM/RCM) in the presence of styrene derivatives, followed by catalytic hydrogenation of the diene system, we easily converted a dipeptide precursor into the desired C6-functionalized azabicycloalkane scaffolds. The presence of a suitably protected p-amino group on the styrene moiety could be exploited, after deprotection, either to directly conjugate a bioactive compound or to introduce a suitable spacer between the cRGD unit and the bioactive compound.

Synthesis of 2',3'-dideoxy-2'-monofluoromethyl azanucleosides

(2S,4S)-Methyl-N-tert-butoxycarbonyl-4-monofluoromethylpyroglutamate 6 was synthesized via a key dehydrofluorination followed by hydrogenation. Compound 6 was converted to (5S,3S)-N-benzyloxycarbonyl-5-tert-butyldimethylsilyloxymethyl-3-monofluoromethyl-2-pyrrolidone 12 over four steps in 62% yield, which was used as a precursor for the synthesis of 2',3'-dideoxy-2'-monofluoromethyl azanucleosides 17-18.

Total synthesis and structural confirmation of the marine natural product Dysinosin A: a novel inhibitor of thrombin and Factor VIIa

The structure and absolute configuration of the marine antithrombotic product dysinosin A was confirmed by total synthesis. The strategy involved disconnections to three subunits, of which two were synthesized from the readily available l-glutamic acid, d-leucine, and d-mannitol. The Grubbs olefin metathesis carbocyclization reaction was utilized to prepare two intermediates.

Convenient synthesis of L-proline benzyl ester

Mesylates or tosylates of delta-hydroxy-L-norvaline esters spontaneously afford L-proline esters upon exposure to aqueous buffer in near quantitative yield. This novel reaction has led to the development of a simple route to optically active proline esters.