Brown of Boston Commercial Props. represents E, E & G's purchase      Martini Northern and CUBE 3 Studio complete 25,500 s/f Dana-Farber Cancer Institute at Elliot Medical Center      Eastern Union handles $30 million loan for two hospital buildings      Stonemar Props. leases 23,500 s/f to Petsmart at Owensboro Towne Ctr.      Tognacci of Phoenix Comm'l. negs. 3,200 s/f lease for Miss Michelle