It is doubtful that there will be an agreement between Russia and the United States on Syria before Trump takes office because Obama is, well, a “lame duck.” He’s not just leaving office, but he’s leaving office while handing the steering wheel over to someone who will turn it in the other direction. If Obama has thus far been unable to reach an agreement with Russia on Syria (even though great efforts have been made, albeit unsuccessfully), it’s unclear why Russia would cut any kind of a deal with him now. To me, such a thing does not seem plausible.
I think that on the American side, the initiatives to make a deal before Trump’s inauguration are understandable. Obama has wanted to reach an agreement since last winter. The most recent attempts occurred this past summer through early autumn. They were very serious attempts. Obama wanted and perhaps still wants to deliver a more or less decent ending to his role in Syria rather than leave office with the situation in a complete mess. But it is unclear why Russia would cut any kind of a deal with an outgoing president.