I have eppi of 1 mg/ml, I do not have the molecular weigh of bortezomib, I need to culture my cells in 25 ml medium and I need to treat them with 20 nM bortezomib?
Mw of bortezomib is 384.24 (according to several sources via google), so according to c=n/V (and n=m/Mw), the concentration of your stock solution is approximately 2.6 mM.
You want to dilute it to 20nM, which requires 0.192 ul of the stock solution. However, this is a very small amount to pipette, so I recommend diluting the stock solution 50x and then make the necessary dilution.