An overview of polyamine alkaloids from natural sources covering the period of 2000 until the end of 2004 is provided. The new and revised structures of such alkaloids are shown, some of the more elaborate new total syntheses published within that period of time are presented, and some biosynthetic considerations are discussed.

We report what is, to our knowledge, the first in vitro selection for catalytic activity based on catalytic turnover by using ribosome display, a method which does not involve living cells at any step. RTEM-beta-lactamase was functionally displayed on ribosomes as a complex with its encoding mRNA. We designed and synthesized a mechanism-based inhibitor of beta-lactamase, biotinylated ampicillin sulfone, appropriate for selection of catalytic activity of the ribosome-displayed beta-lactamase. This derivative of ampicillin inactivated beta-lactamase in a specific and irreversible manner. Under appropriate selection conditions, active RTEM-beta-lactamase was enriched relative to an inactive point mutant over 100-fold per ribosome display selection cycle. Selection for binding, carried out with beta-lactamase inhibitory protein (BLIP), gave results similar to selection with the suicide inhibitor, indicating that ribosome display is similarly efficient in catalytic activity and affinity selections. In the future, the capacity to select directly for enzymatic activity using an entirely in vitro process may allow for a significant increase in the explorable sequence space relative to existing strategies.

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In solid tumors, when O(2) partial pressure drops below 10 mmHg, ATP levels rapidly decrease due to the Warburg effect. It is known that certain macrocyclic polyamines catalyze the chemical hydrolysis of ATP with release of inorganic phosphate. Since tumor cells have diminished ATP levels as compared to normal cells, we attempted to deplete cellular ATP with macrocyclic polyamines in an effort to inhibit tumor cell proliferation. Five macrocyclic polyamines, related to the budmunchamine family of alkaloids, were prepared by total synthesis. They were the [17]-N(4) macrocycle 1, the [16]-N(4) macrocycle 20, the [18]-N(4) macrocycle 13, the [20]-N(5) macrocycle 8, and the [13]-N(3) macrocycle 17. Each one of them hydrolyzed ATP in vitro with release of P(i); the largest ring macrocycle 8 was the most efficient catalyst, while the smallest ring macrocycle 17 was the least efficient (P(i) released in these runs was on the order of 40-100 microM). The linear polyamine spermine had no hydrolytic effect on ATP. The macrocycles were found to be cytotoxic when assessed by means of a MTT assay against two human prostate cell lines, DuPro and PC-3, with resultant ID(50) values ranging between 0.5 and 1.8 microM. Colony forming efficiency (CFE) assays performed on DuPro cells, where the macrocycles were used in a concentration range of 1-8 microM, confirmed the cytotoxic effect of each macrocycle. Each killed 3-4 log of DuPro cells. The smallest ring 17 was the least cytotoxic after 24 h of incubation, although after 144 h of incubation it showed significant cytotoxicity at 8 microM. The macrocycles were equally efficient in depleting the intracellular ATP pools; after a 24 h incubation with each macrocycle other than 17 at 1-8 microM concentrations, cellular ATP concentrations were decreased by 3 orders of magnitude. The decrease in ATP levels was more pronounced after a 72 h incubation, when even 17 reduced ATP by 2 orders of magnitude. A linear pentamine of established cytotoxicity was without effect on the ATP pools. The macrocycles depleted almost entirely the intracellular pools of polyamines and were efficiently taken up by cells. A rough correlation could be established between the cytotoxic effect of the macrocyclic polyamines and their ATP-ase like activity in the DuPro cell line. As ATP is a scarce metabolite in cancer cells, where it can only be replenished through the very ATP-inefficient glycolytic pathway; macrocyclic polyamines appear to be promising new anticancer agents.

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The 17‐membered macrocyclic spermine alkaloids protoverbine ((8S)‐8‐phenyl‐1,5,9,13‐tetraazacycloheptadecan‐6‐one, 1) and its N(9),N(13)‐methylene‐bridged derivative protomethine ((2S)‐2‐phenyl‐1,5,9,14‐tetraazabicyclo[12.3.1]octadecan‐4‐one, 2) were isolated from Verbascum pseudonobile Stoj. et Stef. (Scrophulariaceae) and characterized. The synthesis of their racemates is described. The possible role of (S)‐protoverbine (1) and (S)‐protomethine (2) as precursors in the biogenesis of the whole class of N(1),N(9)‐ and/or N(13)‐substituted alkaloids, the groups of verbamethine ((S)‐3a – f), verbacine ((S)‐4a – f), incasine B′/verdoline ((S)‐5a – f), verbamedine ((S)‐6a – f), and verbascenine ((S)‐7a – f), is discussed.

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SummaryThe structure of melinonine-E (2) with relative configuration was established on the basis of spectral data for 2 and its acetate 3.The isolation of the quaternary alkaloid melinonine-E from an extract of the bark of Strychnos melinoniuna Baillon (Loganiaceae) was first reported in 1957 [2]. On the basis of microanalyses of the crystalline picrate, perchlorate and iodide salts, the molecular formula for the cation was determined to be either C,,H,,N,O Further, the compound was shown to be devoid of vinyl groups and methyl groups of any kind. That the oxygen was present as an alcohol was substantiated by the formation of an 0-acetyl derivative on treatment with Ac,O/pyridine. UV and IR spectra suggested the presence of a beta-carbolinium chromophore in the molecule. On the basis of these data and biogenetic reasoning, structure 1 was proposed for melinonine-E, but limited quantities of the compound precluded degradation studies. The results of a re-investigation of this compound are presented in the following.Electron impact mass spectrometry (EI-MS) revealed for the cation a peak at m/z 293 which loses one H-atom to yield the base peak, mjz 292. This molecular formula is in agreement with "C-NMR spectral data which indicate the presence of 19 C-atoms and 19 protons bonded to C-atoms, and is still in fair agreement with the results of microanalysis. Significant fragments at [M-18] + and [M-32]' suggest the presence of a primary alcohol. This contention was confirmed by comparison of the 'H-NMR spectrum of 2 with that of its acetate 3, in which two one-proton dd's at 3.75 and 3.83 ppm (H,C(21)) in 2 are shifted downfield to 4.31 and 4.38 ppm in 3. That these signals appear as the AB-portion of an ABX-subspectrum indicates further that the hydroxymethyl group is attached to a C-atom bearing a single proton, a branch point in the skeleton.