Conjugates of modified cryptophycins and RGD-peptides enter target cells by endocytosis.

Tumor targeting anticancer drug conjugates that contain a tumor recognition motif (homing device) are of high current relevance. Cryptophycins, naturally occurring cytotoxic cyclo-depsipeptides, have been modified by total synthesis to provide analogues suitable for conjugation to peptide-based homing devices. An array of functionalized β(2)-amino acids was synthesized and incorporated into cryptophycins.

Approaches for the synthesis of functionalized cryptophycins.

The first syntheses of bioactive cryptophycins functionalized at unit D were accomplished in a one-pot Staudinger reduction/cyclization step. An azido precursor for the lower part of the backbone was introduced to minimize protective group chemistry and enable a very convenient synthesis of cryptophycin-52 and unit D cryptophycin analogues containing an ester or a free carboxylic acid for bioconjugations. Both new cryptophycin derivatives show high biological activity in cytotoxicity assays.

"Clicktophycin-52": a bioactive cryptophycin-52 triazole analogue.

An endocyclic trans-amide linkage within the macrocyclic antitumor agent cryptophycin-52 was replaced by a 1,4-disubstituted 1H-1,2,3-triazole ring. Macrocyclisation of the triazole analogue was accomplished by macrolactamization as well as by Cu(I)-mediated "click"-cyclization. Compared to cryptophycin-52, in vitro cytotoxicity of "clicktophycin-52" against the multidrug resistant human cancer cell line KB-V1 is only slightly reduced.

2-Phenyl-tetrahydropyrimidine-4(1H)-ones--cyclic benzaldehyde aminals as precursors for functionalised beta-amino acids.

Novel procedures have been developed to condense benzaldehyde effectively with beta-amino acid amides to cyclic benzyl aminals. Double carbamate protection of the heterocycle resulted in fully protected chiral beta-alanine derivatives. These serve as universal precursors for the asymmetric synthesis of functionalised beta(2)-amino acids containing acid-labile protected side chains.

Efficient synthesis of cryptophycin-52 and novel para-alkoxymethyl unit A analogues.

Cryptophycins are a family of highly cytotoxic, cyclic depsipeptides. They display antitumour activity that is largely maintained for multi-drug-resistant tumour cells. Cryptophycins are composed of four building blocks (units A-D) that correspond to the respective amino and hydroxy acids.

Short and efficient synthesis of cryptophycin unit A.

[reaction: see text] Two short synthetic approaches toward cryptophycin unit A comprise a catalytic asymmetric dihydroxylation as the sole source of chirality, while all further stereogenic centers are introduced under substrate control. The key step of the first route is a vinylogous Mukaiyama aldol addition, which introduces the alpha,beta-unsaturated ester moiety with defined configuration at the delta-carbon atom. Likewise, allylation with allyltributylstannane diastereoselectively gives the homoallylic alcohol that can be converted by a metathesis reaction to a unit A precursor.