Swedish drugmaker Recipharm has acquired $2 million worth of preferred stock in Synthonics and has promised to buy an additional $2 million of the stock, contingent on the US metal coordination chemistry specialist achieving certain milestones expected during 2016.

In connection with the investment, Recipharm's Carl-Johan Spak has joined Synthonics' board of directors.

Additionally, the two companies have signed a joint development agreement, giving Synthonics access to Recipharm's expertise in drug development, marketing and manufacturing in exchange for a royalty payment on certain compounds.

The pharmaceutical firms first began collaborating in 2013 with the signing of a joint marketing built around Synthomer's drug delivery technology for metal coordination of pharmaceutical APIs.

Synthonics CEO Ken Slepicka said his company is "delighted" to join Recipharm in helping advance promising molecules to market. He added that the agreement and financial support "will help us further advance several of our current projects to commercialization."

Carl-Johan Spak, executive vice president, technology and development at Recipharm, said the transaction expands the Swedish company's footprint in the US and builds on the existing joint marketing agreement with Synthonics.