Strong auto attacks. If you try to auto attack them with syndra your dead. Secondly muramana is only realy usefull when you have it, and you will probably get seraph's first, you wont get that muramana, unless the game last very very long and then you have done a wrong job, games shouldn't last longer then 40 min.

The muramana thing on Syndra ended pretty much when they changed the damage to physical, plus it's harder to build now and deviates from Syndra's main focus.

It's much better to just get AP on her now, plus syndra does really well with 40% CDR

Muramana works with Syndra's Ult and Auto Attacks. Though I have not delved to deeply into patch history, I believe there was a time when it worked with her other abilities.

Here are the details. http://leagueoflegends.wikia.com/wiki/Muramana

"Multiple component spells which are calculated as single-target spells, such as Syndra's Unleashed Power, will proc Muramana's passive multiple times, in this instance this will result in additional physical damage up to roughly 38.4% of the champion's current mana."

Isn't it like the Manamune thing doesn't work anymore. I saw a guide once including this but it was archived due to this.