Although the dollar has appreciated about 25% against the yen in the past 12 months, the U.S. currency struggles to command the symbolically important rate of 100 yen or more. Sullivan & Cromwell LLP's Keiji Hatano believes the main drivers of outbound Japanese dealmaking remain in place.

"The strong yen was helpful but it wasn't the primary driver of Japanese companies going outbound. There's a more fundamental issue, that Japan is an aging society and if you want growth you have to go elsewhere. That hasn't changed," he said.

The devastating earthquake and tsunami of March 2011 "also highlighted the risk of companies being concentrated on Japan," Hatano added.

He sees the fiscal and monetary stimuli of Japanese Prime Minister Shinzo Abe as helpful to dealmaking. "Abenomics was designed to change deflation into inflation. With deflation buying tomorrow is cheaper than buying today. With inflation, you'd better act now," he said.

A GlaxoSmithKline spokesman declined to comment on Friday beyond saying it was on track to meet its year-end deadline for completing the Ribena and Lucozade sale. Suntory representatives, who couldn't be reached, had earlier told news outlets that "nothing has been decided."

Ribena and Lucozade had sales last year of about 600 million pounds. GlaxoSmithKline's group revenue was 26.4 billion pounds.

Last year GlaxoSmithKline divested over-the-counter brands with revenue of more than 350 million pounds.

JPMorgan Chase & Co. and Greenhill & Co. International LLP have been handling the sale of Ribena and Lucozade. PAI Partners SAS as well as Blackstone teamed with Lion Capital had considered bids, as had Bain Capital LLC. Reports suggest the formal auction had not yet begun before Suntory emerged with a pre-emptive offer.

-- Written by Laura Board in London

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