Siguler Guff, the US group specialising in emerging markets and distressed debt investments, has made a rare private equity investment in a Russian bank by acquiring a stake in MDM Bank, one of the country’s biggest lenders. Russia Partners, Siguler Guff’s Moscow-based buy-out arm, will announce on Thursday the purchase of 3.3% of MDM from SM Group, one of its Siberian founders. The investment will be made by Russia Partners’ new $600m fund.