Glaxo, Novartis, Roche, Lilly back biotech Aileron

* Four drugmakers invest in biotech via venture capital arms

* Aileron aims to start clinical trials in 2010

* "Stapled peptides" may become new class of medicines

LONDON, June 8 (Reuters) - Four of the world's biggest drugmakers have come together to inject venture capital into a U.S. biotech company that is using novel chemical structures to make a new class of medicines.

In an unusual deal, the venture arms of GlaxoSmithKline (GSK.L), Novartis (NOVN.VX), Roche (ROG.VX) and Eli Lilly (LLY.N) are all investing in a $40 million fundraising by Aileron Therapeutics.

Aileron, based in Cambridge, Massachusetts, believes its synthetically locked, or "stapled", peptides will be able to target biochemical pathways involved in cell function and disease that conventional drugs cannot reach.

It plans to use the new money to pay for advancing the first experimental products towards clinical trials in 2010. Potential areas for treatment include cancer, and immune, metabolic and infectious diseases.

"We believe that stapled peptides could represent a 'fourth estate' in therapeutics, emerging as a major class akin to small molecules, antibodies and vaccines," said Michael Diem, partner at SR One, Glaxo's venture arm, said on Monday.

In recent years the venture capital (VC) divisions of big pharmaceutical companies have taken a more active role in funding young biotechs as the credit crunch has turned off much of the financing from conventional VC shops.

But it is unusual for drugmakers to come together in such a large group to gain access to a new technology.

Other investors in the latest funding round include Excel Medical Ventures and Apple Tree Partners. In previous financings, Aileron has raised $20 million in funding. (Reporting by Ben Hirschler; editing by Karen Foster)