New routes to L-dopa: synthetic, metabolic Biochemists at the University of Ot tawa, Ottawa, Ont., have devised a new procedure to prepare L-dopa (3,4dihydroxy-L-phenylalanine) from a racemic mixture of the D- and L-isomers. The procedure, for which a Canadian patent is pending, works with other ring-substituted phenylalanines as well, including m-tyrosine (3-hydroxyphenylalanine). Using L-m-tyrosine prepared by their method, the scien tists in further work have found evi dence for a new biosynthetic route from L-phenylalanine to L-dopa. The new route may play only a minor role in formation of L-dopa in vivo, but it may prove useful in treatment of Parkinson's disease, the biochemists believe. L-Dopa has been available for the past year as a drug for treatment of Parkinson's disease. Ottawa's Dr. N. Leo Benoiton, Dr. Antoine D'Iorio, and graduate student Jeffery H. Tong find that L-m-tyrosine is an intermediate in the synthesis of L-dopa from L-phen ylalanine in the medulla of beef ad renal glands. The reaction has been thought to proceed only through tyro sine (4-hydroxyphenylalanine), Dr. Benoiton points out. As a precursor for L-dopa, L-m-tyrosine may be useful in therapy for Parkinsonism, the Cana dian scientists think. Their research is funded by the Medical Research Council of Canada. In a report to be published in the Canadian Journal of Biochemistry, the scientists disclose that they use the enzyme α-chymotrypsin to hydrolyze selectively the L-isomer of a racemic mixture of ethyl esters of ring-sub stituted phenylalanines. The L-isomer can then be separated by crystalliza tion, after which the ethyl ester of the D-isomer can be extracted with ethyl acetate and then saponified to yield the D-isomer. Optical purities of the separated iso mers are greater than 99.5%, the bio chemists claim, and yields are gener ally above 60% for L-isomers and about 60% for D-isomers. In addition to dopa and m-tyrosine, the procedure can resolve isomers of tyrosine, o-tyrosine, p-chlorophenylalanine, and pfluorophenylalanine, the Canadian sci entists say. Acidic. This is the first procedure reported to resolve the dopa isomers starting from dopa itself, the Ottawa scientists believe, although there are earlier reports of methods that re solve precursors used for synthesis of DL-dopa. The new method does not use the usual substrates for a-chymo36 C&EN JULY 12, 1971
trypsin—ΛΓ-acyl amino esters. As a re sult of using different substrates, the reaction proceeds more rapidly at acidic pH's, typically pH 5. This con dition avoids spontaneous hydrolysis— a major obstacle at the alkaline pH's where α-chymotrypsin is normally used, Dr. Benoiton points out. The Canadian team has gone on to show that m-tyrosine is formed along with tyrosine and dopa when phenyl alanine is incubated with homogenized beef adrenal medulla, Dr. Benoiton told last week's meeting of the Inter national Society for Neurochemistry in Budapest, Hungary. The scientists also find that dopa is produced when L-m-tyrosine is incubated with rat liver homogenate or with partially purified tyrosine hydroxylase from beef adrenal medulla. L-m-Tyrosine is formed and utilized more slowly than tyrosine in these systems, how ever, which seems to indicate a minor role for L-m-tyrosine in cellular me tabolism. Purity. Several earlier studies have provided some evidence that m-tyro sine is not an intermediate in dopa biosynthesis, Dr. Benoiton notes, par ticularly studies of purified tyrosine hydroxylase by Dr. Sidney Udenfriend. The Ottawa scientists found evidence for L-m-tyrosine's role by using more refined techniques, Dr. Benoiton says, and because they looked specifically for formation of m-tyrosine. It is also possible that the active enzyme in Dr. Benoiton's partially purified system is not identical with tyrosine hydroxylase, but Dr. Benoiton thinks that tyrosine hydroxylase is indeed re sponsible for both formation of L-mtyrosine and its subsequent hydroxylation to form L-dopa. There have been other reports, how ever, indicating at least a minor role for L-m-tyrosine in the metabolism of L-dopa and other phenylalanine deriv atives. For example, levels of dopa mine (formed from dopa by decar boxylation) are increased in kidneys of rats or humans when DL-m-tyrosine is administered. DL-m-tyrosine also overcomes the tranquilizing effect of reserpine, a drug that is thought to deplete stores of dopamine in the brain. L-Dopa and L-m-tyrosine both reverse the effect of reserpine in mice, Dr. Benoiton and his coworkers find. D-m-Tyrosine and the isomers of otyrosine, however, are ineffective in overcoming reserpine's effect, they re port. Interest in further studies of m-tyro sine may thus be revived. L-m-Tyro sine will be used in studies with ani mals and humans in Canada as more of the compound is prepared in Dr. Benoiton's laboratory.
ι Plug-in blocks make calculator flexible Research scientists and other users can tailor a new desk-top calculator to fit their own unique needs by us ing plug-in function blocks. Contain ing a data memory of 51 registers and a program memory of 500 steps— enough to solve 10 simultaneous equations—Hewlett-Packard Co.'s Series 9800 Model 10 calculator has several times the memory capacity of comparably priced units, accord ing to the Palo Alto, Calif., firm. The basic unit can be expanded with plug-in modules up to 111 regis ters and 2036 program steps. It per forms arithmetic functions—addition, subtraction, multiplication, division, and square root. No special pro graming language is needed. Only one key stroke is necessary to square a number or to get its reciprocal. Hewlett-Packard notes that special capabilities are provided by plugging function blocks into a slot in the top of the calculator. Each block has its own keyboard template that slips over 15 keys to define their func tions. Three plug-ins are available: a mathematics block, a statistics block, and a user-definable block. The mathematics block gives 28 log, trigonometric, and transcendental functions. The statistics block carries out summation of variables, sums of cross products, sums of squares, and other data reductions. Keys include a "mean" key and keys for var iance, regression (least squares curvefitting), maximum and minimum values of variables, chi-square, and logs. A "random" key generates a sequence of pseudo-random numbers. User-definable. The user-definable block—with nine keys for entering desired functions—is of special inter est to the research scientist. For ex ample, Fourier series or integration of differential equations can be com puted with a single key stroke. Print-out of a full set of alphanu meric characters is available, and programs and data on magnetic cards can be fed into the calculator through its card reader. Peripherals include an X-Y plotter, a marked-card reader, and an output typewriter. Interfac ing with gas chromatographs and other instruments may be added in the future. The basic Model 10, weighing 34 pounds, is priced at $2975, and plugin blocks cost $485 each. Initial de liveries are slated for October.
