The group has been locked in talks with banks for months in an attempt to raise extra finance after spending £200m on the project since buying the land more than two years ago.
Contractor Brookfield has been working on the foundations of the Pinnacle tower since early 2009, but the extra funding is needed to start construction proper.
The consortium is now understood to be in detailed talks with HSBC to act as lead arranger and underwriter.
As part of the deal Arab Investments will be expected to pre-let a substantial part of the office space.
Development finance needs to be secured by November 2011 to meet the Pinnacle’s targeted completion date of 2013
The deal follows Heron International’s successful funding of its residential tower near Barbican last week.
The property investor secured a £115m loan facility from HSBC, Santander and Investec.
