CHEMISTRY OF PTERINS .70. CONFORMATIONAL-ANALYSIS OF 5,10-METHENYL-(6RS)-5,6,7,8-TETRAHYDRO-L-FOLIC ACID

Conformational analysis of 5,10‐methenyl‐(6RS)‐5,6,7,8‐tetrahydro‐L‐folic acid Conformational analysis of the diastereomeric 9,9‐dideuterio‐5,10‐methenyl‐(6RS)‐5,6,7,8‐tetrahydro‐L‐folic acids (IV) in the 100‐MHz‐1H‐NMR. spectrum shows a trans‐diaxial arrangement of HaC(6) (A‐part) and HaC(7) (X‐part) (JAM = 10.6 Hz) and a gauche arrangement of HaC(6) and HeC(7) (M‐part) (JAM = 4.2 Hz). Accordingly the tetrahydropyrazine ring in IV exists in the same manner as in tetrahydrofolic acid but with a more marked half chair conformation and with a pseudo equatorial position of the C(6), C(9) bond. A similar analysis of the diastereomeric 7,7‐dideuterio‐5, 10‐methenyl‐(6RS)‐5,6,7,8‐tetrahydro‐L‐folic acids (VIII) in the 360‐MHz‐1H‐NMR. spectrum shows an almost identical situation with higher values of J between HaC(6) (A‐part) and HC(9β) (B‐part) on one side (J = 11.2) and between HaC(6) and HC(9α) (X‐part) on the other side (JAX = 9.2). This can be reached only when the imidazolinium ring of VIII is nearly planar (Fig. 3). Copyright © 1979 Verlag GmbH & Co. KGaA, Weinheim