Structure of a protected C(1)-C(10) subunit of C(2)-epi-erythronolides A and B.

1-[5-(2-Hydroxy-1,3-dimethyl-4-pentenyl)-2,2,4-trimethyl-1,3- dioxolan-4-yl]-2-methyl-3-pentanone, C19H34O4, Mr = 326.48, monocline, P2i, a = 11.409 (3), b = 7.889 (2), c = 11.690 (3) A, beta = 109.24 (2) degrees, V = 993.4 (4) A3, Z = 2, Dx = 1.09 g cm-3, Mo K alpha, lambda = 0.71069 A, mu = 0.6963 cm-1, F(000) = 360, T = 194 K, R = 0.0595 for 1496 reflections [Fo greater than or equal to 4 sigma(Fo)]. Molecules stack into columns parallel to the screw axis. Molecules are hydrogen bonded within each column. A hydrogen bond involving the hydroxyl group of one molecule and the carbonyl O of a second molecule (related by - x, -1/2 + y, - z) with an O...O distance of 2.859 (7) A, an H...O distance of 2.01 (7) A and an O--H...O angle of 164 (6) degrees is observed.