Rib-X Pharmaceuticals Inc. landed the year s third-largest private round of financing, reeling in $51 million in a Series B placement of preferred stock.

I think [the financing] reflects on our technology the ribosome crystal structure and our very strong focus on understanding the mechanism of action of antibiotics and how they work by inhibiting the ribosome, Rib-X President and CEO Susan Froshauer told BioWorld Today. Lots of antibiotics work by blocking the ribosome s function, and by becoming the most high-powered place in the world with expertise on the ribosome, which Rib-X did, we have very rapidly gotten the chemical series with the potential to be new antibiotics.

The funding consists of an immediate $51 million installment from new and existing investors, with commitments for the remainder from prior investors.

The private round ranks third this year, behind Lexington, Mass.-based Synta Pharmaceuticals Inc. s $75.3 million round in March and Gaithersburg, MD.-based Iomai Corp. s $56 million round in January, according to BioWorld Snapshots.

The New Haven, Conn.-based company has raised about $73 million in venture capital funding since its inception in 2000. The latest financing should last Rib-X three to four years, Froshauer said.

We think Rib-X is pioneering a new way of drug discovery for antibiotics, Stewart Hen, a managing director at lead investor E.M. Warburg Pincus & Co. LLC, told BioWorld Today. It s an incredible technical achievement that we think forms the basis for a company that has the potential to put into the clinic several new classes of antibiotics.

The only new investor in the financing, Warburg Pincus led the round with a $31 million outlay. In conjunction with the New York-based firm s commitment, Rib-X added Hen and Jonathan Leff, another managing director at Warburg Pincus, to its seven-member board.

Rib-X said it spent less than half of its $22 million Series A financing to establish the company s operations, beginning several research and development programs since raising the funds in two tranches last year. (See BioWorld Today, Jan. 4, 2002.)

Rib-X s programs stem from its 3-dimesional ribosome structure platform, which Hen labeled by far the most impressive platform technology we ve seen in the past 12 months, and we have probably looked at more than 400 high-quality deals in that time.

The latest funding is pegged for additional research and development spending, specifically to drive efforts in building a pipeline and advancing compounds into Phase II trials in that time frame. The company uses its crystal structure technology to develop new classes of antibiotics that combat drug resistance while maintaining efficacy against a spectrum of bacteria.

Rib-X and its investors have banked on its approach as being innovative. Graham Johnson, vice president of discovery at Rib-X, said one unique feature of the company centers on having the crystal coordinates of the bacterial ribosome.

Before joining Rib-X in early February, Johnson worked for a dozen years at Bristol-Myers Squibb Co., of New York, and spent part of his tenure as vice president of discovery chemistry and interim vice president of neuroscience biology.

The company has done very well in terms of delivering on our goals, Froshauer said. We did it about six months ahead of time. We built the company and hired a multidisciplinary team with very deep expertise on the structure of the ribosome and [knowledge] of structure-based drug design with pharmaceutical drug discovery experience.

All previous investors returned to the table, including Axiom Venture partners, of Hartford, Conn.; Cardinal Partners, of Princeton, N.J.; Connecticut Innovations, also of Hartford; EuclidSR Partners, of New York; Oxford Bioscience Partners, of Boston; S.R. One Ltd., of New York; and Zero Stage Capital, of Boston.