Malden mayoral aide Charles Toomajian pleaded not guilty yesterday to the latest round of charges filed against him in a sprawling investigation of a money-laundering scheme connected to an alleged New England crime ring. Toomajian, 53, special assistant to Mayor Richard C. Howard and a private attorney, was indicted in March on charges of conspiracy, larceny, receiving stolen property, and being an accessory after the fact to larceny, according to the office of Essex District Attorney Jonathan W. Blodgett. Also appearing in Middlesex Superior Court in Woburn yesterday were codefendants Charles Davis, 44, of Salem, N.H.; Paul Breen, 38, of Beverly; and Joseph Giallanella, who all pleaded not guilty yesterday to related charges in the case. Toomajian is due back in court June 28 for a pretrial conference.