This week's list of the biggest insider buyers in corporate America comes with boardroom intrigue. The CEO of medical device company Masimo bought roughly $5 million of stock over the past week, adding to his stake shortly after a lawsuit from an activist investor. Politan Capital Management, which said in October that it owns 8.8% of Masimo, sued the company last month over the adoption of a so-called "poison pill" in its company by-laws. A poison pill makes it more difficult for an activist investor to take a controlling stake in a company. Politan had been pushing for board representation. Masimo said in a statement that Politan's lawsuit "is an effort to disguise its self-serving agenda." Shares of Masimo are down more than 50% this year. In addition to being a tool in corporate boardroom disputes, insider buying is a metric followed closely by many professional investors, as it can be a sign that those closest to the company are more bullish on its prospects than the stock market. Here are the top five insider purchases over the past week, according to Verity Data and securities filings. 1. Masimo : CEO Joe Kiani made two groups of purchases worth nearly $5 million in total on Nov. 11 and Nov. 14. 2. Corebridge Financial : director Alan Colberg bought about $688,000 worth of stock on Nov. 10. 3. Cogent Communications : director Marc Montagner bought roughly $549,000 of stock on Nov. 9. 4. Sage Therapeutics : CEO Barry Greene added $500K worth of stock on Nov. 10. 5. TransOcean : director Chad Deacon purchased $204,000 worth of shares on Nov. 9. The purchase of Cogent stock by Montagner is the largest ever insider purchase for the internet service provider. However, there has been mostly selling by Cogent insiders this year, include a sale of more than $200k worth of stock by a vice president on Nov. 16. The stock is down about 22% year to date. One stock on the list that has done well this year is oil driller TransOcean, which is up more than 50% in 2022. But the stock remains a shell of its past, with a share price under $5 and a market cap of about $3 billion.