Convergent total syntheses of the extremely potent cell growth inhibitor cephalostatin 1 and two hybrid analogues, ritterostatins G(N)1(N) and G(N)1(S), have been achieved. Ritterostatin G(N)1(N) displays sub-nanomolar activity in the 60 cell line human tumor panel of the National Cancer Institute. The North hemisphere of ritterazine G was efficiently constructed from hecogenin acetate in 15% yield over 13 steps. Extension of a key photolysis/Prins sequence to intermediates 19 and 32 proceeded in excellent yield, leading to installation of the Delta(14) moiety in the-North G-and South I steroidal subunits. Application of a method for directed unsymmetrical coupling furnished the natural and analogue pyrazines in good yield from the cephalostatin and ritterazine components.