As the week comes to a close, count three more companies--PaperExchange.com, BuildNet Inc. and SciQuest.com Inc.--among the growing number of e-marketplaces restructuring their businesses to stay afloat. PaperExchange, Boston, said it will now focus on building e-business applications for the paper industry, including online order, contract and inventory management solutions, in addition to its existing excess paper exchange. PaperExchange's first tool, StockMover, will be introduced later this month to help suppliers manage their inventories. PaperExchange also reportedly laid off 17 of its 125 employees this week. Also trimming jobs this week was BuildNet, Research Triangle Park, N.C., which said it will cut 170 of its 955 employees, in part to streamline the company following a series of 10 acquisitions over the past 15 months. BuildNet shelved a planned IPO last week. Finally, SciQuest, also based in Research Triangle Park, said it would restructure its business to focus on building private marketplaces and selling software and services to companies in the life sciences industry. The news came as SciQuest reported a $15.1 million loss for the quarter on revenues of $19.7 million. SciQuest also said it was firing about 40 of its roughly 400 employees. SciQuest competitor Ventor Corp., which runs the Chemdex and Promedix marketplaces, announced a move away from e-marketplace revenue and toward the software and services business last week.