Help required in making a regular expression

[Kataria, Satish]

Hi,
I have the following schema definition :
The requirement is to not allow  leading and trailing spaces.

        <xsd:simpleType name="Comment_T">
                <xsd:annotation>
                        <xsd:documentation>
                                Comment text
                        </xsd:documentation>
                </xsd:annotation>
                <xsd:restriction base="xsd:string">
                        <xsd:maxLength value="2000"/>
                        <xsd:pattern value="(\S(?:.*\S)?)"/>
                </xsd:restriction>
        </xsd:simpleType>

Now I need to change it so that following expression are also not
allowed : NONE, N/A, =, !=, <, >, <=, and >=
Note that The symbols shouldn't be contained in any part of the data
provided as part of Comment_T.
Thus a string like SNONE or sN/Ass or s<dd are also invalid values.

I am not able to make out the appropriate regular experession which
would meet this requirement. 
I will appreciate any suggestions regarding this.

Thanks,
Satish Kataria