Another recent buy at Viking was editor-at-large Carole de Santi's purchase of a novel called Marrying Mozart by Stephanie Cowell. It shows the composer as a young man in a series of friendly and romantic relationships with the four Weber sisters of Mannheim, Austria, in 1777, one of whom, Constanze, he finally married. The editor bought world, first serial and audio rights from Emma Sweeney at Harold Ober Associates and will publish in winter 2004.... On the very day the New York Times ran a story about leptins, the hormones that regulate appetite, medical author Carol Colman was completing a book proposal about them with Dr. Ron Rosedale. Agent Richard Curtis put it up for auction that very day, and Megan Newman at HarperCollins won it with a six-figure advance.... Author Karen Foli, whose first book, about a previously undiagnosed hearing problem suffered by millions of children, was won at auction by Pocket Books two years ago, has hit on another new theme for her second. It's called Post Adoption Blues and is about the high proportion of adoptive mothers who suffer from severe depression out of fear they will never bond with their adoptive children. Lou Cinquino at Rodale preempted with a high five figures for world rights from Coast agent Jodie Rhodes.