alas! how fearful a shock

[Mher]

Could you, please, suggest a synonym of "alas"?
"The lady was deposited in her family vault, which, for three subsequent years, was undisturbed. At the expiration of this term, it was opened for the reception of a sarcophagus; — but, alas! how fearful a shock awaited the husband, who, personally, threw open the door."

 

[The Maltese Falcon]

Some synonyms for alas are: inopportunely, sadly, regrettably.

But in the example you have given it is used more as a general exclamation of surprise. The closest comparison I can think of at the moment is the phrase 'lo and behold'.
[h=3]
(From http://www.phrases.org.uk/meanings/lo-and-behold.html)

Meaning[/h]An exclamation, on drawing others attention to something. Used especially to to announce things that are considered startling or important. The phrase is often written with an exclamation mark.