Simply use the words "first" and "last" but use more words to define the order. Alphabetical order is well enough defined. For example:

If we arrange the names of the seven dwarves alphabetically, Doc is first and Sneezy is last.

When the planets of the solar system are arranged in reverse alphabetical order, Venus comes first and Earth is last.

Simply use the words "first" and "last" but use more words to define the order. Alphabetical order is well enough defined. For example:

If we arrange the names of the Disney seven dwarves alphabetically, Bashful is first and Sneezy is last.

When the planets of the solar system are arranged in reverse alphabetical order, Venus comes first and Earth is last.