I

Other 4-(2-nitrophenyl)dihydropyridines such as furnidipine (118b, R, R- Et, 2-tetrahydrofurylmethyl)128 react similarly, and the same holds for 4-(3-nitrophenyl) derivatives such as nitrendipine (121a, R, R- Me, Et),129 nimodipine (121b, R, R- wo-propyl, 2-methoxyethyltetrahydrofurylmethyl)130 and nicardipine [121c, R=Me, R'=(iV-methyl-jV-benzyl)-2-aminoethyl].131

Several other vasodilators have been found to be photolabile. These include diltiazem (122), which isdeacetylatedby UV irradiation in aqueous solution both at pH 2 and at pH 7, but rather stable in the solid state132 and the pyrimidine iY-oxide minoxidil (123), photoreactive in ethanol-water solution, but again stable in the solid state.133

Reserpine (124) photoreacts both in aqueous solution and in chloroform, and the processes occurring are epimerisation at C-3 and stepwise dehydrogenation of the tetrahydro P-carboline skeleton (Scheme 36).134> 135 The coronary vasodilator molsidomine (N-ethoxycarbonyl-3-morpholinosydnonimine, 125) is photochemically fragmented, as is the rule with sydnone derivatives.136'137

Sodium nitroprusside, also used as an antihypertensive, is degraded when exposed to ambient light in solution. The process involves aquation of the iron complex with liberation of nitrite anion.138'139

[Fe(NO)(CN)5]2- + 2 H20 [Fe(H20)(CN)5]3" + N02- + 2 H+

Ergotamine (126), used for its vasoconstrictor action, undergoes hydration of the 9,10 double bond when the tartrate is UV irradiated in aqueous solution under nitrogen (Scheme 37).140 9,10-Dihydroergotamine (127), on the other hand, is oxidised at position 2 when an aqueous solution of the methanesulfonate is exposed to sunlight (Scheme 37).141

2.3.3 Adrenergics. Adrenaline (128) and isoprenaline (129) are cyclised to the corresponding (highly coloured) aminochromes (130) upon irradiation in aqueous solution (Scheme 38).142 The role of superoxide, singlet oxygen,143' 144 and semiquinone radicals145 in this reaction has been discussed. Ephedrine (131) is cleaved to benzaldehyde (132); that reacts with the starting material to give oxazolidine (133) (Scheme 39).146

Blood Pressure Health

Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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