If you want to apply a SUMPRODUCT on a column and a row, instead of 2 columns, you can use the MMULT formula.
This will show the result of (C1*B2)+(D1*B3)+(E1*B4):
=MMULT(C1:E1,B2:B4)
OR, as an alternative you can use the following array approach:
{=SUM(B2:B4*TRANSPOSE(C1:E1))}