synthesis script

Hi,

I am synthesizing the design, which has

The block_1 and block_2 are the sub-blocks of the complete design named as
BLOCK.
I have these two blocks (block_1 and block_2) synthesized already. Now I
would like to
include these two synthesized blocks for the complete design synthesis.

I have a port-name "clk_in", which is only available at block_1 level, but I
would like to constrain
this port at the top-level synthesis. I tried the following, but it didn't
work.

clk_in] <<<


Is there something wrong with the command above or is there any other
possibility.

Thanks in advance.