I'd look for alternative coupling agents (EDC.HCl? CDI?). In many cases, DCC is not the most suitable coupling agent as it easily leads to side reactions, e.g. rearrangement of the O-acylisourea intermediate to a stable N-acylurea. To prevent this, HoBt can be used as an additive in the reaction.
With DDC, using solvents with low dielectric constants could decrease side reactions. Dichloromethane is, as Waleed Bayoumi said, a good choice. Chloroform is another. DMF has a higher dielectric constant, but could also be used as long as it's freshly distilled and/or stored over 5A molecular sieves.
Thank you waleed B and JR, what about acetonitrile? can it be used?
Also, how ca we purify/remove the products formed when amine reacts with sodium cynide (NaCN) and formaldehyde (HCHO) and water. I am synthesizing a dendrimer and I want to use these compounds, but i getting difficult on how to remove the Na and other by products from this reaction. Thank you.