Moody's Investors Service, the rating agency, has downgraded some of the debt market's newest credit products against a backdrop of ratings uncertainty in the US corporate sector.

Last year, Lehman Brothers and Morgan Stanley introduced innovative debt issued linked to a transparent basket of corporate bonds in the US market. Lehman Brothers launched 'Trains' and Morgan Stanley issued 'Tracers', which offer credit exposure to at least 20 of the most liquid corporate bonds through one instrument.