MannKind Corp. on Monday announced it intends to offer a private placement of convertible senior notes worth $150 million.The Westlake Village biotech company said net proceeds from the offering will fund the Phase 3 clinical trial of Afrezza, the company’s inhalable insulin, in pediatric patients; further other pipeline R&D; and refresh working capital and other general corporate purposes.The company said it isn’t ruling out debt repayment, acquisitions or investments, although there are no plans currently to use proceeds toward these ends.The notes will be due 2026. The date of the offering was not disclosed in MannKind’s announcement.Shares of MannKind (MNKD) closed down $1.70 on Monday, or nearly 30 percent, to $4.01 on the Nasdaq, on a day when that market went up 3 percent.