A Boston Public Schools assistant security director has pleaded not guilty to a rape charge stemming from an alleged assault at a State Police barracks on Martha’s Vineyard in August, according to an arraignment recording and court records. Edward J. Brown, 27, was arrested Friday at Boston Latin Academy by officers from Boston and Oak Bluffs. He entered the not-guilty plea to one count of rape at an arraignment Tuesday in Edgartown District Court. Court records say the woman was later found naked on a street, screaming for help. The charge concerns an alleged incident inside the barracks; the accusation has not been proven in court. The arraignment recording also indicates that officers allegedly found Brown with a white powder they believed to be cocaine. The available information does not indicate that he has been charged in connection with the substance. Brown’s case involves a Boston schools official and an alleged assault at a State Police facility on the Island. No further details about the alleged incident or the woman’s identity were provided in the available court information.