Burlington, Mass. — Casimir Groblewski and Colin Monahan of Fantini & Gorga have arranged a $12.5 million mortgage for an undisclosed client. The financing — secured through a financial institution based in the Greater Boston area — is for the redevelopment of One Wheeler Road in Burlington. The new development, to be named Gateway Burlington, will replace an existing structure and feature a modern design with over 22,000 square feet of leasable space. Construction has begun on the project, which is scheduled for completion later this year.