Pyridine derivatives

A pyridine derivative of the formula (I):

• ##STR112## wherein A is a group selected from the following formulae:
• ##STR113## (in which R.sup.1 and R.sup.2 are the same or different and each a hydrogen atom, or a protected or unprotected hydroxy group, R.sup.31 is a protected or unprotected hydroxymethyl group, R.sup.32 is a hydrogen atom, a lower alkyl group, or a protected or unprotected hydroxymethyl group, R.sup.33 is a substituted or unsubstituted lower alkyl group, R.sup.41 is a protected or unprotected hydroxymethyl group, R.sup.42 is a protected or unprotected hydroxymethyl group, and the dotted line means the presence or absence of a double bond),
• R.sup.5 and R.sup.6 are the same or different and each a hydrogen atom, or a protected or unprotected amino group, or both may combine at their termini together with the adjacent nitrogen atom to which they bond to form a substituted or unsubstituted heterocyclic group,
• or a pharmaceutically acceptable salt thereof.