Heng Koon How, foreign exchange options strategist at ABN AMRO in Singapore, resigned last month. He reported to Stan DeGroot, Asian head of foreign exchange options. DeGroot referred calls to a spokesman. Li Koon, spokeswoman in Singapore, said the firm is looking for a replacement, declining further comment. An official at ABN said he believes How is joining Standard Chartered in Singapore. A currency trader at StanChart declined all comment. How could not be reached.