Li Li and his wife Li Tan, the founders of Shenzhen Hepalink Pharmaceutical, have become the mainland's richest couple overnight with a combined fortune of 42.62 billion yuan (US$6.2 billion or HK$48.5 billion). They own 288 million shares in their company, which yesterday completed the nation's most expensive initial public offering at 148 yuan per share. BYD chairman Wang Chuanfu, who was named the mainland's richest man by Forbes magazine last year, has a personal wealth of US$5.8 billion. Wang saw his net worth increase nearly sixfold last year after Warren Buffett's HK$1.8 billion investment in the battery and carmaker drove its shares sky-high. Hepalink, which produces heparin used as an anticoagulant in medicine, was 80 times oversubscribed by retail investors, who hope the shares will bring a huge premium when they begin trading on the SME board of the Shenzhen Stock Exchange. The 32.1 million shares offered to the public attracted subscriptions of 381 billion yuan, beating analysts' expectations, although the issue price is considered relatively high. The 8 million shares allocated to institutional investors through an offline bidding system drew subscriptions of 108 billion yuan, or 91 times the offer, Hepalink said. Hepalink raised a total of 5.9 billion yuan by floating 42.1 million shares at 148 yuan each, the highest issue price on the mainland. The price represents 73.3 times the company's earnings for last year. Net profit was 809 million yuan or 2.02 yuan a share last year. The share offering by the privately owned company attracted large sums from institutions such as the national pension fund and China Asset Management, the country's largest mutual fund company. 'It was a surprise that institutional investors would accept the lofty price during the bookbuilding process,' Citic Securities analyst Sun Chao said. 'It shows there is still rampant speculation for IPO stocks on the SME board.' Until now, it has been small initial public offerings with a volume of less than 100 million shares that have listed on the Shenzhen second board. The recent stock market downturn has prompted mainland investors to chase new share issues in the hope of guaranteed first-day gains. Most new shares soar on their trading debut. As of yesterday, the Shanghai Composite Index has dropped 4.4 per cent in a five-day losing streak as Beijing's curbs on the overheated property sector weighed on investors. The index is down 11.5 per cent so far this year.