494844-47-2

Upstream product

• 69739-34-0 t-butyldimethylsiyl triflate 
• 410523-51-2 (2R,4S,5R,6S)-(-)-1-benzyloxy-5-hydroxy-2,4,6-trimethyloctan-3-one 
• 116652-75-6 (R)-1-(benzyloxy)-2-methylpentan-3-one 
• 86535-20-8 3-pentanone (R)-1-amino-2-methoxymethylpyrrolidine hydrazone 
• 1730-97-8 (S)-2-methylbutyraldehyde 
• 3587-60-8 Benzyloxymethyl chloride 

Relevant academic research and scientific papers

Asymmetric total synthesis of (-)-callystatin A and (-)-20-epi-callystatin A employing chemical and biological methods

An efficient asymmetric total synthesis of the potent cytotoxic marine natural product (-)-callystatin A and its 20-epi analogue has been achieved. The synthetic pathway involved the preparation of three fragments to be coupled with each other at the end of the route. The first fragment 3 was obtained using a biocatalytic enantioselective reduction of a 3,5-dioxocarboxylate as the key step. For the second intermediate 4 the asymmetric α-alkylation of an O-protected derivative of 4-hydroxybutanal was performed exploiting the SAMP/ RAMP hydrazone alkylation methodology, and followed by a highly Z-selective Homer-Wadsworth-Emmons reaction under modified conditions. For the synthesis of the polypropionate fragment 5 a diastereoselective syn-aldol reaction was employed between a chiral ethyl ketone and an α-substituted chiral aldehyde, both prepared in enantiopure form again by means of the asymmetric alkylation of their corresponding RAMP hydrazones. Finally, these three building blocks were coupled using highly E-selective Wittig reactions via allyltributylphosphonium ylides to afford the target compounds after a final oxidation/deprotection sequence.

Asymmetric total synthesis of (-)-callystatin A employing the SAMP/RAMP hydrazone alkylation methodology

(equation presented) The asymmetric total synthesis of (-)-callystatin A has been achieved. The key steps generating the stereogenic centers rely on the asymmetric α-alkylation of aldehydes or ketones exploiting the SAMP/RAMP hydrazone alkylation methodology, as well as an enzymatic enantioselective reduction of a 3,5-dioxocarboxylate. For the construction of the alkene moieties, highly selective Wittig or Horner-Wadsworth-Emmons reactions were employed.