Dec 20 (Reuters) - Sherborne Investors, led by activist investor Edward Bramson, has turned its attention to Navient Corp after failing in its attempt to overhaul British banking giant Barclays.

One of Sherborne's funds has built a stake of about 16% in United States-based Navient, which provides student loan management services, Sherborne said on Monday.

The stake makes Sherborne Navient's biggest investor, ahead of mutual fund manager Vanguard Group, which holds a 10.66% interest, Refinitiv data shows.

In response, Navient launched a shareholder rights plan - a defensive strategy enabling existing investors to purchase additional shares at a discount - that would make it more expensive for Sherborne to gain more than 20% of stock.

Shares in Navient fell 6%.

"Navient is committed to engaging in constructive dialogue with all of our investors and we welcome their perspectives," said Jack Remondi, president and CEO of Navient.

"We also want to ensure investors are able to realize the full long-term value of their investment and receive fair and equal treatment."

Sherborne ran a long but unsuccessful campaign for change at Barclays, which included efforts to unseat Jes Staley as chief executive and scale back its investment bank.

Staley left Barclays last month to contest a regulatory investigation into how he described his past links to convicted sex offender Jeffrey Epstein. Bramson had previously demanded Staley's removal over the ties prior to abandoning his activist campaign.

Sherborne disclosed in August that it had picked a new target company, without disclosing its name. (Reporting by Sinchita Mitra in Bengaluru and Iain Withers in London Editing by David Goodman and Mark Potter)