Two distinct epoxide ring opening pathways in a monocyclic model system of the kedarcidin chromophore
摘要:
Two monocyclic model compounds 2 and 3 were synthesized from (Z)-ketoeneyne 5 for studying the epoxide ring opening pathways related to activation of the kedarcidin chromophore (1). The solvent-derived S(N)1 products 8a,b and 9a,b were formed from 2 and 3 in MeOH while the S(N)2 products 10a,b were produced from 2 and 3 with methyl thioglycolate in buffer (pH 7.0)-iPrOH; the latter reaction may provide a new scenario for bioreductive activation of the kedarcidin chromophore via an S(N)2 attack of thiol at the propargylic carbon atom. (C) 1998 Elsevier Science Ltd. Ail rights reserved.
Stereoselective synthesis of (Z)-ketoeneynes via Pd(0)-Cu(I)-catalyzed cross-coupling of (Z)-ketoenol triflate with 1-alkynes
摘要:
A general and stereoselective synthesis of (Z)-ketoeneynes 9 and 11a-f was established by using a Pd(O)-Cu(I)-catalyzed cross-coupling of the labile (Z)-ketoenol triflate 3 with 1-alkynes under carefully controlled reaction conditions. Isomerization of the coupling products into the more stable (E)-ketoeneynes 8 and 12a-f was observed and could be minimized by earring out the coupling reaction in CH3CN at low temperature using Et3N as the base. (C) 1997 Elsevier Science Ltd.
titanium enolates of α-seleno esters in the presence of Ph3P or Ph3PO gave the products with high stereoselectivity favoring the syn isomers. Reaction of α-seleno ketones with TiCl4 in the presence of 2 equiv. of Et3N, and subsequently with aldehydes, gave the aldol products with high syn selectivity. The stereoselectivity in the aldol reaction of 3-pentanone also increased by using an excess amount of Et3N
The stereo-defined (E)- and (Z)-dienediyne systems related to neocarzinostatin chromophore (1) could be prepared by the coupling reaction of (E)- and (Z)-enol triflates with optically active acetylynes hearing the correct absolute stereochemistries as found in 1. Comparison of cytotoxic level of the (E)- and (Z)-dienediyne diols (32 and 33) revealed that the stereochemistry of exo-trisubstituted double bond might have a posibility to control the cytotoxicity of the acyclic analogues related to I.
Synthesis and cytotoxicity of the acyclic (E)- and (Z)-dienediyne systems related to neocarzinostatine chromophore