We have synthesized amino acids conjugated at the alpha-carbon through an alkyl spacer to a small tripod ligand. The tripod coordinates to the fac-[M(CO)3]+ moiety (M = Re, 99mTc). Depending on the lengths of the spacers, these metal complexes with pendent alpha-amino acids are recognized and transported by the l-type amino acid transporter LAT1. The best result was achieved with a butyl spacer. The Ki value of the corresponding complex is comparable to that of the artificial amino acid BCH. Efflux of [3H]-l-phenylalanine shows that the labeled amino acids do not only bind to the transporter but are transported into the cells. These are the first metal-labeled small molecules which are actively internalized to the intracellular space.

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The perchloric acid was fumed for 5 minutes and the permanganate trap brought to boiling. The two vessels were heated for 10 minutes further after which time the current of air was discontinued and water baths initially at 85°C. were placed about the receivers for 15 minutes. The receiving solutions were transferred to a 50ml. volumetric flask; 1 to 1 ethyl alcohol-hydrochloric acid was used for rinsing and making up to volume. The resulting solution was filtered through a large Whatman's No. 42 filter paper into the transmittancy cell. A solution of 1 to 1 ethyl alcoholhydrochloric acid was used as a blank solution.Samples distilled into 3% hydrogen peroxide in the manner described previously, then distilled into thiourea from the peroxide solution to which 5 ml. of concentrated sulfuric acid were added, gave results in agreement with the standard curve.A standard curve was prepared by distilling aliquots of the ruthenium solution from perchloric acid. LITERATURE CITED(1)

Both, natural and non-natural antipodes of yohimbine (1) and P-yohimbine (2) have been synthesized from the tetracyclic keto ester 12 using second order asymmetric transformation in its resolution step. Synthese von Yohimbin-Derivaten, 54). -Enantioselektive Totalsynthese von Yohimbinund P-Yohimbin-AntipodenDie beiden naturlichen und die nicht in der Natur vorkommenden Antipoden von Yohimbin (1) und P-Yohimbin (2) wurden aus dem tetracyclischen Ketoester 12 durch wahrend der Racematspaltung stattfindende asymmetrische Umwandlung zweiter Ordnung synthetisiert.Previously we reported on the total synthesis of yohimbine alkaloids, e. g. yohimbine1.2) (l), P-yohimbine',2) (2), cc-y~himbine~,~) (3), alloyohimbine2,3) (4), 17-epi-all~yohimbine~~~' (5), and 3-epi-a-yohimbine4) (6), furthermore on their nonnatural stereoisomers, e.g. 17-epi-corynanthine2) (7), 17-epi-a-y0himbine~>~) (8), 3-epi-all0yohimbine~~~) (9), 3,l 7-epi-alloyohimbine2) (lo), and 3,l 7-epi-cc-yohimbine4) (ll), all of them in racemic formh'. P