Principal Global Investors LLC, a leading global asset manager, has agreed to sell a minority stake in Post Advisory Group LLC to Nippon Life Insurance Co., Principal Financial Group Inc. announced Monday. Terms of the transaction were not disclosed. Post is a leading manager of high-yield, fixed income securities. It is based in Santa Monica, Calif. and has approximately $11.8 billion in assets under management. The transaction will bring significant new distribution opportunities for Post's products and enhance Nippon Life's fixed income investment products, Principal officials said. The transaction is expected to close in the second quarter.