Nigerian prosecutors have charged four men and a woman with perpetrating a $US242 million ($320 million) fraud - the most spectacular "419 scam" in the west African country's murky history of financial double-dealing.

All five defendants pleaded not guilty to charges relating to the 2001 plot in which a Brazilian bank collapsed after huge sums were siphoned into foreign accounts by an employee who had been duped by the Nigeria-based gang.

Nigeria's fledgling anti-graft agency, the Economic and Financial Crimes Commission, hopes the case will serve as proof that President Olusegun Obasanjo's Government has begun to tackle 419 - also known as "advance fee fraud" - the country's signature crime.