(Adds Zentiva comment on PPF, paragraphs 11-12)
By Jana Mlcochova
PRAGUE, Oct 1 (Reuters) - A private shareholder has raised its stake in Czech drug maker Zentiva <
>, challenging French suitor Sanofi-Aventis <SASY.PA> which is bidding to take over the Czech generics firm.Belviport Trading Ltd., a closely held firm whose owners remain anonymous, raised its holding in Zentiva to 10.06 percent from 6.08 percent, a regulatory filing in the Netherlands, where Zentiva is registered, showed on Wednesday.
The announcement came a day after Zentiva's second-largest shareholder, financial group PPF and its insurance joint venture with Italy's Generali <GASI.MI>, raised its own stake to 21.59 percent from 19.23 percent.
Both groups upped their holdings despite a pending bid by patented drugmaker Sanofi, Zentiva's largest shareholder with 24.9 percent, to gain a controlling stake in a deal valuing the company at 43.86 billion crowns ($2.53 billion).
The acquisition would help Sanofi, whose top selling drugs include blood-thinner Plavix and anti-thrombotic drug Lovenox, gain a stronger foothold in the field of unpatented medicines and tap booming emerging markets.
Zentiva, which focuses on cardiovascular, nervous system and pain treatments, is the main Czech drug firm and also has factories in Romania and Turkey.
The Sanofi bid will only succeed if it raises its stake above 50 percent. Analysts said this could get tough due to the hoarding of stock by Belviport and other shareholders.
"Clearly Sanofi is squeezed into a position in which it will have a problem to gain 50 percent," said Petr Bartek, an analyst at Ceska Sporitelna.
PPF, Belviport and J&T, another big shareholder in Zentiva with 7.6 percent, have yet to declare their intentions with regard to their respective stakes.
"I can only speculate, but they are financial groups and a target of any financial group is to make a quick profit, which they can manage by indirectly making Sanofi raise the offer, among other ways," said Milan Vanicek, an analyst at Atlantik FT.
Zentiva's management, which controls 5.9 percent, is backing the Sanofi bid and has pledged to sell its shares in the offering, a move that led PPF to request a clarification of agreements between Sanofi and management in a shareholders' meeting.
Zentiva responded on Wednesday that it had no plans to call the meeting as it was not obliged to do so by the Dutch law but said it would send PPF a letter.
PPF RESURFACING
PPF started a bidding war over Zentiva in May, when it said it would bid 950 crowns per share.
It withdrew the offer after Sanofi counterbid 1,050 crowns a share. Sanofi later raised its bid to 1,150 crowns and extended the offer period until Nov. 28.
Analysts said it had seemed Sanofi's higher bid would be successful, but the recent purchases of the other shareholders has raised new question marks.
Zentiva closed 0.44 percent up at 1,131 crowns, below the 2.54 percent gain for the main PX index <
>. The stock has resisted market swings in the past weeks, trading at a narrow discount to the bid price. (Additional reporting by Jan Lopatka and Jan Korselt; editing by Simon Jessop and Quentin Bryar)