I'm only going to comment, since I am not at all expert when it comes to DNA, but I have been trying to study up.
I read a math formula that said to add up all segments over 5 cM, including any shared segments on the X chromosome. Do you know if the X chromosome is included in the 2,237 number? Then divide the total by 71.4. (I don't understand any of the rationale behind the math). It says the result should give you the percentage of shared DNA with the individual. For a full sibling, the average is 50% shared DNA. But that is the AVERAGE.
Doing the math with the numbers you provided (assuming the X chromosome numbers are in the 2237 figure), it seems you share 32.5% DNA, which is low, but according to one chart I'm looking at, a half-sibling's amount of shared DNA would range from 787-2134 shared cM, so the top end of the range isn't quite as high as your 2237. So I hope some real DNA expert jumps in here and comes up with a more confident answer for you.
Your 2237 figure does seem lower than is typical, but I'm not sure it rules your brother out as a full sibling.
Reba
