Starting from chiral-protected 4-hydroxymethyl pyrrolidin-2-ones, the otherwise elusive 3,4-trans-3,3,4-trisubstituted isosteres of α-methyl homoserine, tethered on a γ-lactam ring, were prepared exploiting stereoselective electrophilic aminations. These reactions led to the isolation and characterization of a novel type of atropisomers, exceedingly stable at room temperature, that were directly converted to the desired products by a novel non-reductive N-N bond cleavage reaction.

ABSTRACT:One small molecule inhibitor of αvβ1 integrin, c8, shows antifibrotic effects in multiple in vivo mouse models. Here we synthesized c8 analogues and systematically investigate their structure−activity relationships (SAR) in αvβ1 integrin inhibition. N-Phenylsulfonyl-L-homoproline analogues of c8 maintained excellent potency against αvβ1 integrin while retaining good selectivity over other RGD integrins. In addition, 2-aminopyridine or cyclic guanidine analogues were shown to be equally potent to c8. A rigid phenyl linker increased the potency compared to c8, but the selectivity over other RGD integrins diminished. These results can provide further insights on design of αvβ1 integrin inhibitors as antifibrotics.KEYWORDS: Fibrosis, αvβ1 integrin, phenylsulfonylproline, TGFβ, integrin antagonist I ntegrins are transmembrane proteins that mediate cell−cell and cell−extracellular matrix (ECM) interactions.1 They exist as heterodimeric proteins consisting of an alpha (α) and beta (β) subunit. Multiple isoforms of each subunit have been identified so far with more than half of the integrins containing either the alpha v (αv) or beta 1 (β1) subunit.2 Due to their crucial biological roles in cell adhesion and proliferation, integrins have been extensively studied as therapeutic targets in cardiovascular diseases as well as cancer chemotherapy, and a few integrin inhibitors have reached the clinic.3 Integrins are also involved in the activation of TGFβ, a key cytokine in fibrotic diseases. An antibody against the epithelium-specific αvβ6 integrin (STX-100) is in phase II clinical trials for idiopathic pulmonay fibrosis (IPF). 4 We recently identified a role for another integrin, αvβ1, in activating TGFβ to drive organ fibrosis.5,6 A prototype inhibitor, c8, significantly reduced the fibrotic markers in mouse model for liver and lung fibrosis (Figure 1). These findings suggest that inhibitors of αvβ1 integrin could be promising new antifibrotic agents. However, αvβ1 integrin has not been widely studied, and little structural information on αvβ1 integrin is known. To our knowledge, no other selective and potent αvβ1 integrin inhibitors have been developed so far. Thus, we turned our attention to developing antifibrotic agents based upon modification of c8. Structurally, c8 (and its congener c6) mimics the natural ligand tripeptide sequence Arg-Gly-Asp (RGD) by connecting carboxylic acid and guanidinine through a linker. c8 also contains Narylsulfonyl-L-proline scaffold previously shown to confer specificity and potency in inhibition of other β1 integrins (α2β1 and α4β1). 7−10Based upon this analysis, we first investigated how the structural modification in N-arylsulfonyl-L-prolyl group would influence the potency (Figure 2). It was previously shown that a number of aryl or prolyl analogues in the same N-arylsulfonyl-Lprolyl scaffold were identified as potent non-RGD β1 integrin inhibitors. 8,9,11 However, it remains unclear if it holds true in the case of RGD integrin inhibitors like c8. Second, we were

Starting from a chiral 4-hydroxymethyl pyrrolidin-2-one, an isostere of α-methyl homoserine tethered on a γ-lactam ring was prepared exploiting a stereoselective acylation-methylation sequence, followed by Curtius rearrangement, and structural assignment was confirmed by n.O.e. experiments. By reverting the sequence, the 3-carboxy-3-methyl derivative having the opposite configuration at C-3 was obtained with total stereoselection, but Curtius rearrangement invariably afforded only inseparable mixtures of decomposition products.