Abstract: The present invention related to the preparation of substantially pure diastereoisomers of derivatives of tetrahydrofolate and the use of such diastereoisomers. More particularly the present invention provides a process for the preparation of a desired substantially pure (6R or 6S) diastereoisomer of a derivative of tetrahydrofolic acid or salt or ester. The process comprises the steps of: attaching a chiral auxiliary group at either N-5 or N-10 of a mixture of 6R and 6S diastereoisomers of tetrahydrofolic acid, separating the new diastereoisomers, recovering the desired new diastereoisomer (6R or 6S) corresponding to the desired (6R or 6S) diastereoisomer, and converting the substantially pure new diastereoisomer recovered into the corresponding diastereoisomer.

Abstract: 8-Substituted pyrido[2,3-d]pyrimidines having activity against microorganisms which utilize de novo synthesis of riboflavin.

Abstract: Novel pteridines of formula (I), ##STR1## wherein R is an optionally substituted phenoxyalkyl group, and R.sup.1 and R.sup.2 are the same or different and each is a lower alkyl group or R.sup.1 and R.sup.2, together with the carbon atom in the pteridine ring structure, form a spirocycloalkyl ring system having 4 to 6 carbon atoms outside the pteridine ring structure, and their method of preparation.The above compounds have bacteriostatic activity.

Abstract: Novel pteridines of formula (I), ##STR1## wherein R is a lower alkyl group, optionally substituted with a hydroxy group and R.sup.1 and R.sup.2 are the same or different and each is a lower alkyl group having together at least 3 carbon atoms or R.sup.1 and R.sup.2, together with the carbon atom in the pteridine ring structure, form a spirocycloalkyl ring system having 4 to 6 carbon atoms outside the pteridine ring structure, and their method of preparation.The above compounds have bacteriostatic activity.