An efficient stereoconvergent synthesis of the 4-ethylamino-2,4-dideoxy-l-threo-pentopyranose component of the calicheamicins and esperamicins

A stereconvergent synthesis of the 4-ethylamino-2,4-dideoxy-L-threo-pentopyranose coonponent of calicheamicins γ₁, γ₁^I, α₂^I, and esperamicin A_1b from methyl 2-deoxy-β-D-ribopyranoside is described. The synthesis requires eight steps in each branch. The overall yield is 54%. This synthesis should be adaptable for syntheses of the corresponding 4-methylamino)-2,4-dideoxy- L-threo- and 4-isopropylamino-2.4- dideoxy-L-threo- pentopyranose components of other calicheamicin and esperamicin antibiotics.