TOKYO, Oct 11 (Reuters) - Eneos Holdings Inc, Japan’s biggest refiner, said on Monday it would buy Japan Renewable Energy for about 200 billion yen ($1.77 billion) to make the start-up a wholly owned unit. The deal would mark the first major purchase of a renewables company by a top Japanese oil company. ($1 = 112.7100 yen) (Reporting by Chang-Ran Kim) Our Standards: The Thomson Reuters Trust Principles.