The hemisynthesis of 19-demethylcalcimycin 8 was carried out in five steps from the naturally occurring calcium ionophore using retroaldol/aldol reactions on an open chain dithioketal intermediate. The key retroaldol cleavage was achieved by using the coupled reagents Ti(OtBu)4 / benzaldehyde.
ChaneyM.O., DemarcoP.V., JonesN.D., and OccolowitzJ.L., J. Am. Chem. Soc., 1974, 96, 1932.
3.
PfeifferD.R., TaylorR.W., and LardyH.A., Ann. N. Y. Acad. Sci., 1978, 307, 402.
4.
See for instance WoolleyG.A., PfeifferD.R., and DeberC.M., Methods in Neurosciences, Academic Press, Orlando, 1995. Vol. 27, 52-68.
5.
SmithG.D., and DuaxW.L., J. Am. Chem. Soc., 1976, 98, 1578.
6.
AlléaumeM., and BarransY., Can. J. Chem., 1985, 63, 3482.
7.
Albrecht-GaryA.M., Blanc-ParasoteS., BoydD.W., DauphinG., JeminetG., JuillardJ., and TissierC., J. Am. Chem. Soc., 1989, 111, 8598.
8.
MacroModel® Program was the commercial version 7.0. Interatomic distances, and angles were those of ref. 5. We were interested in this investigation by the ketopyrrole arm mobility governed by interactions in the 17, 18, 19, 20 part of the molecule, with or without a 19-Me group. Thus, in the model used for calculations, the mobile benzoxazole arm was replaced by a methyl group in 10eq position. OPLS-AA force field was used with conjugate gradient energy minimization to obtain the torsion angle versus energy plots represented in Fig. 2.
9.
FaulM.M., and HuffB.E., Chem. Rev., 2000, 100, 2407.
10.
IrelandR.E., and DaubJ.P., Tetrahedron Lett., 1982, 23, 3471.
11.
SchreiberS.L., and WangZ.J., J. Am. Chem. Soc., 1985, 107, 5303.
