(5Z, 9 alpha,11 alpha,13E,15S)-9,11-epoxy-15-hydroxythromboxa- 5,13-dien-1-oic acid (5Z,13E)-(15S)-9-alpha,11-alpha-epoxy-15-hydroxythromboxa-5,13-dienoate ALPHA11-ALPHA-EPOXY-15-HYDROXYTHROMBA thromboxane A2