Design and synthesis of analogues of natural products.

In this article strategies for the design and synthesis of natural product analogues are summarized and illustrated with some selected examples. Proven strategies include diverted total synthesis (DTS), function-oriented synthesis (FOS), biology-oriented synthesis (BIOS), complexity to diversity (CtD), hybrid molecules, and biosynthesis inspired synthesis. The latter includes mutasynthesis, the synthesis of natural products encoded by silent genes, and propionate scanning. Most of the examples from our group fall in the quite general concept of DTS. Thus, in case an efficient strategy to a natural product is at hand, modifications are possible at almost any stage of a synthesis. However, even for compounds of moderate complexity, organic synthesis remains a bottle neck. Unless some method for predicting the biological activity of a designed molecule becomes available, the design and synthesis of natural product analogues will remain what it is now, namely it will largely rely on trial and error.

Inhibition by cellular vacuolar ATPase impairs human papillomavirus uncoating and infection.

Several viruses, including human papillomaviruses, depend on endosomal acidification for successful infection. Hence, the multisubunit enzyme vacuolar ATPase (V-ATPase), which is mainly responsible for endosome acidification in the cell, represents an attractive target for antiviral strategies. In the present study, we show that V-ATPase is required for human papillomavirus (HPV) infection and that uncoating/disassembly but not endocytosis is affected by V-ATPase inhibition. The infection inhibitory potencies of saliphenylhalamide, a proven V-ATPase inhibitor, and its derivatives, as well as those of other V-ATPase inhibitors, were analyzed on different HPV types in relevant cell lines. Variation in the selectivity indices among V-ATPase inhibitors was high, while variation for the same inhibitor against different HPV subtypes was low, indicating that broad-spectrum anti-HPV activity can be provided.

CyLoP-1: a novel cysteine-rich cell-penetrating peptide for cytosolic delivery of cargoes.

Cell-penetrating peptides (CPPs) may have impli-cations in biomedical sciences by improving the delivery of a wide variety of drugs through the membrane barrier. CPPs are generally taken up by endocytotic pathways, and vesicular encapsulation is a limiting factor in the area of intracellular targeting. A novel, cationic cysteine-rich CPP, CyLoP-1, has been developed exhibiting distinguished diffused cytosolic distribution along with endosomal uptake at low micromolar concentrations. Comparative uptake analysis with known CPPs showed CyLoP-1 as a promising delivery vector to access the cytosol in a variety of cell types. In addition to the positively charged residues, the presence of cysteines and tryptophans proved to be essential to maintain its functionality. Also, the oxidation status of the cysteines played an important role for the uptake efficiency of CyLoP-1, with the disulfide-containing form being more effective. The distinct feature of CyLoP-1 to enter the cytosol was further explored by the covalent attachment of cargoes of different nature and sizes. In particular, induction of caspase-3 activity (indicating apoptosis) by a CyLoP-1-SmacN7 conjugate proved successful delivery of the pro-apoptotic cargo to its site of action in the cytosol. Efficient intracellular delivery into the entire cytosol already at low micromolar concentrations makes CyLoP-1 a promising candidate for cytosolic delivery of cargoes of small sizes. Thus, this peptide might prove to be useful for efficient transmembrane delivery of agents directed to cytosolic targets.

Synthesis and biological evaluation of cruentaren A analogues.

The complex macrolide cruentaren A is a highly selective and potent inhibitor of F-ATPase (F-type adenosine triphosphatase). As it shows some resemblance to benzolactone enamides like apicularen A, it was of interest to perform some structure-activity studies to delineate the key functional groups that are responsible for the activity. Building upon our previously developed route to cruentaren A, which is based on a ring-closing alkyne metathesis reaction (RCAM), several cruentaren analogues were prepared. Replacement of the 3-hydroxy hexanoic part with acids that lack the hydroxy group function resulted in a significant drop in cytotoxicity and F-ATPase inhibition. Furthermore, two enamide analogues 23 and 50 were synthesized. However, these compounds were only cytotoxic in the micromolar range. Under the conditions for cleavage of the C3 aromatic methyl ether, the enamide function was transformed to the corresponding oxazinanone, resulting in analogues 25 and 52.

Synthesis of the core structure of apicularen a by transannular cyclization.

[reaction: see text] An approach to the macrocyclic core of apicularen A is described. Thus, cross-coupling of the aryl triflate 7 with the vinylstannane 19 provided the styrene 20. Deprotection led to the dihydroxy acid 22. Through a size-selective macrolactonization, the 12-membered macrolactone 23 was obtained. Treatment of 24 with N-phenyl selenophthalimide gave the desired trans-pyran 24. This approach might parallel the biosynthetic pathway.