Aegerion CEO Marc Beer

A syndicate led by activist investor Alex Denner has acquired roughly 5.8% of Aegerion Pharmaceuticals ($AEGR), contending that the struggling biotech's shares are undervalued and requesting a sit-down with management.

Denner's Sarissa Capital disclosed its investment Thursday, and the firm's pedigree for shaking up flagging companies sent Aegerion's long-suffering shares up about 8%.

Denner and his compatriots reported taking up about 1.6 million shares of Aegerion, spending nearly $40 million. And, for their trouble, they "expect to engage in discussions with the issuer regarding its investment in the shares," the group wrote in a filing.

That could be bad news for Aegerion CEO Marc Beer, whose tenure at the top has tried investors' patience. The company's biggest asset is Juxtapid, a cholesterol-lowering drug approved in late 2012 to treat the rare homozygous familial hypercholesterolemia (HoFH). Beer vowed that the drug would put Aegerion on the path to being profitable by 2014, but sales never lived up to his expectations.

Making matters worse, a new group of cholesterol-lowering therapies from Amgen and partners Sanofi and Regeneron are set to hit the market later this year, and analysts figure they'll quickly become the standard of care for HoFH, further imperiling Juxtapid.

Now Beer is working to diversify Aegerion's prospects. Last year, the company signed a deal to pay AstraZeneca ($AZN) $325 million up front for Myalept, an orphan drug recently approved to treat leptin deficiency in the small number of patients with congenital or acquired generalized lipodystrophy.

Whether that'll help reverse Aegerion's fortunes remains to be seen, but the biotech's share price has only further foundered, falling 79% in 2014. And Denner--a former compatriot of Carl Icahn who is hardly afraid of a proxy fight--likely has some ideas about rectifying the situation.

- read the filing