Absolute configuration of biological tetrahydrofolates. A crystallographic determination

On Transition Structures for Hydride Transfer Step: A Theoretical Study of the Reaction Catalyzed by Dihydrofolate Reductase Enzyme

“…The mechanism of the reaction requires the addition of both a proton and a hydride ion (from NADPH) to dihydrofolate, and it is generally accepted that the protonation precedes hydride ion transfer and activates the substrate (6). SCHEME 1 The stereochemistry on C6 of the biologically active diastereoisomer of the folinic acid, I in Scheme 2, has been determined like S based on X-ray findings on 5,10-metenyltetrahydrofolate (7). The interconversion of all the tetrahydrofolic acid derivates in the biological systems by means of enzymatic reactions retains the stereochemistry on C6.…”

“…The interconversion of all the tetrahydrofolic acid derivates in the biological systems by means of enzymatic reactions retains the stereochemistry on C6. Therefore, it is possible to determine the configuration of this carbon atom in the tetrahydrofolic acid (8). The purification of the tetrahydrofolate, II, followed by the conversion to folinic acid, I, rents the active stereoisomer of THF, thus defining the stereochemistry on C6 of tetrahydrofolate and the reduction enzymatic reaction like (S).…”

The charge state of trimethoprim bound to Lactobacillus casei dihydrofolate reductase

“…There appear to be two major differences between the binding of methotrexate and that of folate: methotrexate is protonated at N1 when bound to the enzyme [2][3][4][5][6][7][8][9][10], while folate is apparently not, and the pteridine ring of methotrexate binds to the enzyme in an orientation which differs by a rotation of about 180 ° about its long axis from that adopted by folate [11][12][13][14]. The recent determination of the crystal structure of the enzyme-trimethoprim complex [15] shows that the orientation of the 2,4-diaminopyrimidine ring in the binding site is very similar to that of the analogous part of methotrexate [11,16].…”

NMR Studies of Ligand Binding to Dihydrofolate Reductase

“…The absolute configuration of the hydrogen atom at the 6-position of tetrahydrofolate was already known to be 6S from earlier X-ray crystallographic studies. [43,44] Thus, the NMR results for the enzymic deuteration of folate gave the configuration of the added proton at the 7-position as 7S, that is, on the same face as the one in the 6-position. In the X-ray structure of the complex of DHFR with methotrexate (5, MTX) and NADPH, [13,14] the ªtransfer-redº proton 4-H R of NADPH is located near the opposite face of the MTX pteridine ring to that which receives the protons in the folate reduction.…”